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Revision of chromosome numbers of Potamogetonaceae:
a new basis for taxonomic and evolutionary implications
Revize variability v počtu chromozomů a její důsledkypro taxonomii a evoluci v čeledi Potamogetonaceae
Zdeněk K a p l a n, Vlasta J a ro lí m o v á & Judith F e h r e r
Institute of Botany, Academy of Sciences of the Czech Republic, CZ-252 43 Průhonice,
Czech Republic, e-mail: kaplan@ibot.cas.cz, jarolimova@ibot.cas.cz, fehrer@ibot.cas.cz
Kaplan Z., Jarolímová V. & Fehrer J. (2013): Revision of chromosome numbers of Potamo-
getonaceae: a new basis for taxonomic and evolutionary implications. – Preslia 85: 421–482.
In order to establish a sound basis for systematic and evolutionary research, we determined the chro-
mosome numbers of 181 samples of 47 species and 32 hybrids of Potamogetonaceae from 27 coun-
tries and areas, ranging from Greenland in the north to New Zealand in the south and reevaluated
previously published counts. The first counts are reported here for 10 species and 25 hybrids of
Potamogeton and for 1 species and 3 hybrids of Stuckenia. Both homoploid and heteroploid hybrids
were identified, as well as hybrids resulting from the fusion of reduced and unreduced gametes.
Three previously undetected hybrids of Potamogeton are described and validated as P. ×drepa-
noides,P. ×luxurians and P. ×serrulifer. The extensive within-species variation in chromosome
numbers sometimes reported in the literature was not confirmed. Chromosome numbers appeared
to be generally species-specific in Potamogetonaceae; the only exceptions were two sterile
autotriploid plants detected within two otherwise fertile diploid Potamogeton species. Furthermore,
chromosome numbers were often uniform even within species groups or genera and to some degree
also clade-specific in phylogenetic trees based on nuclear ribosomal markers (ITS and 5S-NTS
regions). In the largest genus, Potamogeton, there are two base numbers for diploids (x = 13 and x = 14)
and three ploidy levels in species (diploids, tetraploids and octoploids; all polyploids were based on
x = 13), in Stuckenia only hexaploids (also based on x = 13) occur and Groenlandia is monotypic
with x = 15. A critical evaluation of the published counts revealed three major sources of error: (i)
methodological problems due to difficult karyotypes, (ii) approximations based on wrong precon-
ceptions and (iii) poor taxonomic treatments, misidentified species or unrecognized hybrids. We
estimate that about 24% of the counts in original publications and up to 41% in chromosome atlases
and indices are doubtful or demonstrably erroneous. Most of these were from a relatively few dubi-
ous sources whereas the majority of counts reported in the literature correspond to our findings.Two
alternative scenarios for the evolution of chromosome numbers in this family are discussed in
a phylogenetic context, with either x = 13 or x = 14 as the base chromosome number in the family;
the base number of x = 7 suggested by some authors is refuted. In both scenarios, several aneuploid
transitions between these karyotypes and a single change towards x = 15 have to be assumed.
Polyploidizations are rare in this family and mostly associated with major evolutionary events.
A single or a very few events led to a large species group of tetraploids in Potamogeton, and two
subsequent rounds of polyploidization can explain the cytotype of Stuckenia, in which speciation
took place entirely at the hexaploid level. Three octoploid species of Potamogeton had allopoly-
ploid origins. This study gives an example of how the careful re-examinationof chromosomenum-
bers can substantially ameliorate interpretations of systematic and phylogenetic patterns.
K e y w o r d s: aneuploidy, base number, chromosome number, cytotaxonomy, evolution, heteroploid
hybrid, internal transcribed spacer, karyology, phylogeny, ploidylevel, polyploidy, reduced gamete,
5S non-transcribed spacer
Preslia 85: 421–482, 2013 421
Introduction
Chromosome number is an important cytological character that substantially influences
various biological and evolutionary characteristicsof an organism and is used for evaluat-
ing relationships and taxonomic decisions (Stace 2000). Its value is acknowledged in
many recent taxonomic and biosystematic studies (e.g. Felix & Guerra 2010, Krahulec et
al. 2011, Rooks et al. 2011, Rotreklová et al. 2011, Šafářová et al. 2011, Štěpánek et al.
2011, Dančák et al. 2012, Koutecký et al. 2012a, b, Kúr et al. 2012). However, both sys-
tematic and geographical representation of chromosome records is highly uneven. Bennett
(1998) estimated that chromosome numbers of more than 70% of angiosperm species are
unknown. Most chromosome counts are for relatively well-known plants from temperate
and boreal regions of Europe. Even for these species, this information may be incomplete
because the counts are often made on only one individual. The proportion of incorrect
counts and counts made on misidentified material is unknown, but may be surprisingly
high, as can be deduced from the high number of recent studies commenting on previous
doubtful or erroneous records (e.g. Krahulcová 2003, Marhold et al. 2005, Mártonfi et al.
2008, Mráz et al. 2008, Rotreklová et al. 2011, Dančák et al. 2012, Letz et al. 2012, Vít et
al. 2012). Many taxonomically difficult groups and plants from poorly explored regions
are largely neglected. The proportion of species for which the chromosome number is
known is less than 1% in some little-collected tropical areas (Stace 2000).
The Potamogetonaceae are one of the most diverse and taxonomically difficult fami-
lies of aquatic plants (Wiegleb &Kaplan 1998, Kaplan 2002a). The main sources of taxo-
nomic complexity include their reduced morphology, which limits the number of taxo-
nomic characters that can be used to separate species (Preston & Croft 1997, Kaplan &
Štěpánek 2003, Kaplan et al. 2009), an extensive phenotypic plasticity (Kaplan 2002b,
2008, Kaplan & Zalewska-Gałosz 2004), partitioning of genetic variation between rather
than within populations (Hettiarachchi & Triest 1991, Kaplan & Štěpánek 2003) and the
occurrence of numerous hybrids (e.g. Preston 1995, Wiegleb & Kaplan 1998, Kaplan &
Fehrer 2007, Kaplan et al. 2009, Kaplan 2010a). The Potamogetonaceae include about 80
species and 105 hybrids classified into three genera, namely Potamogeton with about 72
species and 99 hybrids, monotypic Groenlandia, and Stuckenia with 7 species and 6
hybrids (Kaplan 2008, 2010a, c, and unpublished data). The highest species and hybrid
diversity is found in temperate regions of the Northern Hemisphere.
Previous records indicate considerable variation in chromosome number in
Potamogeton and Stuckenia. There are two reviews of the chromosome numbers in
Potamogeton s. l. (i.e. incl. Stuckenia). (i) Les (1983) intended to bring together reports of
chromosome numbers in the literature and discuss them in the context of taxonomic and
phylogenetic relationships within Potamogeton. He concludes that the genus is character-
ized by two different polyploid lineages (one based on x = 7 and the other on x = 13) and
that the diploid level of the genus is 2n = 14. Unfortunately, this study included many
errors that mainly resulted from poor taxonomic background and reliance on secondary
chromosome compilations rather than on the original publications (see below). It was crit-
icized by Wiegleb (1988) because the listing of chromosome counts is incomplete, the
attribution of synonymy is incorrect in some cases and the assignment of species to mor-
phological groups erroneous. Consequently, this review did not show any reasonably clear
pattern and the implications for the evolution of chromosome numbers in pondweeds were
422 Preslia 85: 421–482, 2013
doubtful. (ii) Hollingsworth et al. (1998) thoroughly revised all published counts and com-
pared records abstracted in chromosome indices and compilations with those in the origi-
nal publication, and highlighted numerous errors in the literature. The most important out-
come of this review is the clear demonstration that many chromosome counts in secondary
literature are misreported or even never made. The authors emphasize that the use of sec-
ondary literature presents many pitfalls.
In their worldwide account of Potamogeton species and hybrids, Wiegleb & Kaplan
(1998) note that two or more methodologically reliable chromosome counts are available
only for about 30 of the 69 recognized species and 4 of 50 confirmed hybrids. All counts
are for plants from the Northern Hemisphere. For at least 20% of the published counts,
Wiegleb and Kaplan were not sure to which taxon they actually refer. They identified that
the obtaining of reliable chromosome counts of well identified specimens, both from the
Northern Hemisphere, but in particular from the Southern Hemisphere, is one of the major
tasks of future Potamogeton research.
Only a small number of new records have been published since the last review by
Hollingsworth et al. (1998). Less than half of the species have been studied cytologically.
The literature continues to include much contradictory information about chromosome
numbers in Potamogetonaceae, and there is still no consensus about the base numbers in
this family (Hollingsworth et al. 1998, Wang et al. 2007). The aims of this paper are there-
fore to (i) fill some of the gaps in the knowledge of chromosome numbers in Potamo-
getonaceae, (ii) compare new counts with published records, (iii) evaluate all available
chromosome numbers and, as far as possible, distinguish repeatedly confirmed counts
from unique doubtful records never confirmed by other researchers, (iv) analyse the pat-
tern in the variation in chromosome numbers against morphological and taxonomic
groups and in a phylogenetic framework based on well identified specimens and represen-
tative intraspecific genetic variation, and (v) identify the base chromosome number.
Material and methods
Plant material
Samples of plants of Potamogetonaceae from 27 countries from all over the world were
collected in the field from 1993–2012 and cultivated in the Experimental garden of the
Institute of Botany, Průhonice, Czech Republic. Altogether, 242 samples of species and
hybrids of Potamogeton,Stuckenia and Groenlandia were studied. All samples were
identified based on the latest knowledge and an ongoing taxonomic revision of the family
for the world monograph of the family within the project Species Plantarum – Flora of the
world (Z. Kaplan, in preparation). DNA analysis was used to confirm the identity of all
hybrids listed in this study (J. Fehrer & Z. Kaplan, unpublished data, if not indicated other-
wise). Many of the samples investigated were also used in parallel studies on phenotypic
plasticity (Kaplan 2002b), artificial hybridization (Kaplan & Fehrer 2006), genetic varia-
tion (Kaplan & Štěpánek 2003) and hybrid identification based on molecular markers
(Kaplan et al. 2002, 2009, 2011, Kaplan & Fehrer 2004, 2007, 2009, 2011, 2013, Kaplan
& Wolff 2004, Kaplan 2007). The system of reference numbers used here is common to all
these studies. Voucher specimens are preserved in the herbarium of the Institute of Botany,
Průhonice (acronym PRA).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 423
Chromosome counts
Cultivated plants were used for most of the chromosome counts. Exceptions are samples
1533, 1534, 1535, 2072, 2074, 2076, 2077, 2251 and 2252, material of which was col-
lected in the field. Chromosome numbers were determined at mitotic metaphase in
somatic cells of actively growing root tips; only the gametic number for sample 2072 was
established using pollen mother cells from young flower buds. The root tips were collected
from roots growing from horizontal shoots (rhizomes) or, lessfrequently, from stem bases.
Usually, about 10 root tips per sample were taken.
The root tips were pre-treated in a saturated water solution of p-dichlorbenzene for
approximately two hours then fixed in a 3:1 mixture of 96% ethanol and acetic acid, mac-
erated in a 1:1 mixture of ethanol and hydrochloric acid for 30 s, washed in water and
stained with lacto-propionic orcein. The flower buds were treated in a similar way to the
roots, only the pre-treatment was omitted. The number of chromosomes was determined
under a Carl Zeiss Jena NU microscope equipped with an Olympus Camedia C-2000
Z camera and Olympus E – 510 Digital SRL Camera.
Root sampling and chromosome counting of each sample was repeated (up to eight
times) until at least three clear and well-spread metaphase preparations allowed the identi-
fication of a reliable count. Approximate counts (uncertain interpretations of the karyo-
types ± 1–2 chromosomes) are indicated in the following text by „ca“. Of the 242 samples
studied, chromosome numbers of only 181 are recorded here. The remaining preparations
contained only mitotically inactive cells or the observations were inconclusive and were
excluded to avoid publishing incorrect counts.
In order to avoid shaping the results according to expectations, samples were generally
collected by ZK and studied karyologically under anonymous numbers by VJ. Taxon
names were assigned to the samples only after the chromosome numbers were established.
Molecular procedures and data analyses
In order to assess the distribution patterns in chromosome number in a phylogenetic
framework, two nuclear ribosomal sequence regions were chosen, the internal transcribed
spacer (ITS) and the 5S non-transcribed spacer (5S-NTS). Both markers have been used
previously in phylogenetic studies of Potamogetonaceae (Wang et al. 2007, Lindqvist et
al. 2006) and differ in their levelof sequence variation. To visualize the relationships of the
three genera the less variable ITS region was used. In this analysis, all available Stuckenia
species and monotypic Groenlandia were represented by two accessions each whereas for
Potamogeton, each available diploid species was represented by one plant. Based on the
ITS analyses, the basal-most Potamogeton taxa were chosen as an outgroup for addressing
the intrageneric relationships with the 5S-NTS, because this region was too variable to
allow a reliable alignment with the other two genera. For 5S-NTS analyses, diploid and
tetraploid species were mostly represented by two accessions each; additional representa-
tive genotypes were included if the intraspecific variation was high (J. Fehrer et al., unpub-
lished data). From among these, we selected preferentially those individuals for which the
chromosome numbers were determined, and for which the geographic origins were as
broad as possible. Hybrids were not used in the construction of the tree, with the exception of
cloned 5S-NTS sequences (see below) of the diploid sample identified as P. groenlandicus,
which turned out to be of hybrid origin. Octoploid taxa were also excluded as they represent
424 Preslia 85: 421–482, 2013
allopolyploids originating from various combinations of tetraploid parental species
(J. Fehrer et al., unpublished data). A list of the samples used in the molecular analyses is
given in Appendix 1.
DNA isolations, PCR-amplification and sequencing of the ITS region were done as
described in Kaplan & Fehrer (2004). For amplification of the 5S-NTS, primers 5SPI2
(5'-tgggaagtcctcgtgttgca-3') and 5SPIIm (5’-gtagtgctggtatgatcgca-3’) were used; both
were modified after Cox et al. (1992). PCRs were performed in 25 μl reactions containing
1 mM MgCl2, 200 μM of each dNTP, 0.2 mM of each primer, 2.5 μl of Mg2+-free reaction
buffer and 0.5 units of Taq DNA-polymerase (MBI Fermentas / Thermo Fisher Scientific,
Ontario, Canada) and a few nanograms of genomic DNA. Pre-denaturation was done at
95°C for 5 min, followed by 32 cycles of 95°C for 30 s, 50°C for 30 s and 72°C for 20 s,
and a final extension step at 72°C for 10 min. PCR products were purified using the
QIAquick PCR purification kit (Qiagen, Hilden, Germany) and sequenced with both PCR
primers at GATC Biotech (Cologne, Germany). Sequence editing, treatment of
polymorphisms and cloning of one hybrid sample (see above) were done as described in
Fehrer et al. (2009). Sequences were submitted to the GenBank database; accession num-
bers are included in Appendix 1.
Sequence alignments of both datasets were done by hand in Bioedit V7.0.9.0 (Hall
1999) and incrementally improved using the Guidance Server (Penn et al. 2010a) and
a combination of the algorithms Guidance (Penn et al. 2010b) and MAFFT (Katoh et al.
2005). The final alignments used for analyses are available upon request. Indel coding for
both datasets was done with FastGap V.1.2 (Borchsenius 2009) based on the simple
method of Simmons & Ochoterena (2000). Phylogenetic analyses were performed
employing Neighbor Joining (ITS), Maximum Parsimony (ITS, 5S-NTS) and Bayesian
inference (5S-NTS) using PAUP* 4.0b10 (Swofford 2002) and MrBayes (Ronquist &
Huelsenbeck 2003). Neighbor Joining analysis was done using P-distances; bootstrapping
was performed with 1000 replicates. Maximum parsimony analyses (both datasets) were
done as heuristic searches with 100 random addition sequence replicates and TBR branch
swapping, saving no more than 100 trees with length ≥1 per replicate. Bootstrapping was
done using the same settings and 1000 replicates, but without branch swapping. Prior to
Bayesian analysis, the model of molecular evolution best fitting the data was determined
using Modeltest V3.5 (Posada & Crandall 1998). In hierarchical Likelihood Ratio Tests,
a K81uf+G model was determined of which the basic model parameters (six substitution
rates and gamma distribution) were used as priors for Bayesian inference along with the
default settings. Chains were computed for 2 million generations, sampling every 1000th
tree. The first 25% of the trees per run were discarded as burn-in and the remaining trees
summarized.
New chromosome counts and discussion on particular species and hybrids
In the genera Potamogeton and Stuckenia, species are listed first (in alphabetic order), fol-
lowed by hybrids; hybrids with a binomial are listed first followed by unnamed ones. The
samples under each taxon are ordered according to the reference numbers that are given in
bold.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 425
Groenlandia densa (L.) Fourr.
2n = 30
970:S
WITZERLAND, canton Graubünden: western edge of Champfèrer See (lake) by Silvaplana near St. Moritz,
ca 46°28'N, 09°48'E, alt. 1789 m, 17 VI 1998, coll. Z. Kaplan 98/70, cult. & coll. Z. Kaplan 970. – 988:A
USTRIA,
Vorarlberg, Bregenz: narrow inlet on sandy alluvium on left bank of mouth of Bregenzer Aach River flowing into
Bodensee (Lake Constance) at the N–NNE edge of Hard, 47°30'04"N, 09°41'47"E, alt. 396 m, 23 VI 1998, coll.
Z. Kaplan 98/136, cult. & coll. Z. Kaplan 988.
This is the only species of the genus Groenlandia. It is distributed mainly in western,
central and southern Europe, in south-western Asia and northernmost Africa. Our counts
agree with previous records for Sweden (Palmgren 1939), Czech Republic (Krahulcová
1988), Slovakia (Uhríková in Májovský et al. 2000) and Austria (Hasitschka-Jenschke
1959). The only record that differs is 2n = 12 for Italy (Peruzzi & Cesca 2002). The figure
presented in that paper shows a karyotype with chromosomes too robust and of a different
shape to those of G. densa. We therefore suspect that this count was made on misidentified
plant material from another family.
Potamogeton acutifolius Link
2n = 28
321:C
ZECH REPUBLIC, distr. Pardubice: Baroch fispond 0.7 km SSW of Hrobice, 50°05'51.6"N, 15°46'55.3"E, alt.
224 m, 9 IX 1996, coll. Z. Kaplan 96/628, cult. & coll. Z. Kaplan 321 (Fig. 1g). – 1542:C
ZECH REPUBLIC, distr.
Česká Lípa: Držník fishpond in forest 1.1 km ESE of Hradčany, 4 km S of Mimoň, 50°36'37"N, 14°43'23"E, alt. 273 m,
11 IX 2004, coll. Z. Kaplan, cult. & coll. Z. Kaplan 1542. – 2074:C
ZECH REPUBLIC, distr. Hradec Králové: Dolní
Flajšar fishpond 0.6 km WSW of Štít, 50°06'50.6"N, 15°28'02.5"E, alt. 216 m, 23 V 2009, coll. Z. Kaplan 09/58.
2n = ca 28
1158:C
ZECH REPUBLIC, distr. Jindřichův Hradec: Velký Panenský fishpond 1.3 km SSE of Lomnicenad Lužnicí,
49°04'05"N, 14°43'50"E, alt. 420 m, 8 IX 1999, coll. Z. Kaplan 99/157, cult. & coll. Z. Kaplan 1158.
So far, only a single chromosome count has been published for this species of temper-
ate regions of Europe. This was determined by Palmgren (in Löve & Löve 1942) as 2n =
26 based on material from Scandinavia, presumably southern Sweden. As all our samples
of P. acutifolius and all other species of the P. compressus group (sensu Kaplan & Marhold
2012) investigated in this study invariably have 2n = 28 at the diploid level, we consider
Palmgren’s count as inexact. It may have been estimated, rather than counted exactly,
under the mistaken belief that all Potamogeton diploids have 2n = 26. The karyotype of
sample 321 includes a pair of chromosomes with satellites (Fig. 3a).
Potamogeton alpinus Balb.
2n = 52
338:CZECHREPUBLIC, distr. Hradec Králové: backwater pool (detached river arm) of Orlice River at north-eastern
edge of Malšova Lhota, 50°12'30"N, 15°53'16"E, alt. 232 m, 8 X 1996, coll. Z. Kaplan 96/681, cult. & coll.
Z. Kaplan 338 (Fig. 2a).
According to published data, this species has the same chromosome number through-
out its circumboreal distribution. The new chromosome count presented here is in accor-
dance with all previous records, which came from Sweden (Palmgren 1939, as n = 26),
426 Preslia 85: 421–482, 2013
Iceland (Löve & Löve 1956), Japan (Harada 1956, Takusagawa 1961), Siberia (Probatova
et al. 2008a), Russian Far East (Probatova & Sokolovskaya 1986, 1988, as P. tenuifolius),
Canada (Löve 1954a, Löve & Löve 1975b, 1981) and Greenland (Dalgaard 1989). The
record for Spain (Löve & Kjellqvist 1973, as 2n = 26, “corrected” in Löve & Kjellqvist
1974 to 2n = 52) is erroneous as material they studied was actually of P. polygonifolius
(see under this species).
Potamogeton amplifolius Tuckerm.
2n = 52
1689: USA, New Hampshire, Carroll Co.: Upper Danforth Pond 5 km WNW–W of Freedom, 43°49'33"N,
71°06'26"W, alt. 124 m, 29 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/414, cult. & coll. Z. Kaplan 1689.
Our count for this North American species is in agreement with both previous records
based on plants from Minnesota, USA (Stern 1961, as n = 26) and Manitoba, Canada
(Löve & Löve 1981).
Potamogeton berchtoldii Fieber
2n = 26
174:R
USSIA, Siberia, Buryatia, Baikal area, distr. Barguzinskiy, Barguzinskaya Basin: oxbow of Ina River 4 km
NNW of Jubilejnyj, ca 53°45'28"N, 110°11'26"E, alt. 495 m, 2 VIII 1993, coll. Z. Kaplan 93/518a, cult. & coll.
Z. Kaplan 174. – 910:C
ZECH REPUBLIC, distr. Ústí nad Orlicí: second of five fishpondsin castle park at south-east-
ern edge of Žamberk, 50°04'59.1"N, 16°28'35.1"E, alt. 413 m, 14 IX 1997, coll. Z. Kaplan 97/907, cult. & coll.
Z. Kaplan 910. – 925:C
ZECH REPUBLIC, distr. Hradec Králové: ditch at pond in forest 2.8 km NE of Vysoké
Chvojno, 50°07'43.7"N, 16°00'22.9"E, alt. 269 m, 4 IX 1996, coll. Z. Kaplan 97/837, cult. & coll. Z. Kaplan
925. – 927:C
ZECH REPUBLIC, distr. Rychnov nad Kněžnou:drainage ditch in forest sand-pit 1.3 km E of Týniště
nad Orlicí, 50°09'03.8"N, 16°06'23.4"E, alt. 260 m, 5 IX 1997, coll. Z. Kaplan 97/852, cult. & coll. Z. Kaplan
927. – 930:C
ZECH REPUBLIC, distr. Ústí nad Orlicí: pool in abandoned part of granite quarry at northern edge of
Litice nad Orlicí, 0.6 km NE of castle, 50°05'26.9"N, 16°21'16.4"E, alt. 460 m, 11 IX 1997, coll. Z. Kaplan
97/877, cult. & coll. Z. Kaplan 930. – 1160:C
ZECH REPUBLIC, distr. Přerov: ditch in meadows at west-north-west-
ern edge of Chropyně, 49°21'48.5"N, 17°21'17.1"E, alt. 194 m, 14 IX 1999,coll. Z. Kaplan 99/158, cult. & coll.
Z. Kaplan 1160. – 1648: USA, Vermont, AddisonCo.: fast flowing section of Otter Creek just at confluence with
New Haven River 1 km W of Brooksville, Weybridge, 44°03'45"N, 73°10'39"W, alt. 67 m, 25 VII 2005, coll.
Z. Kaplan & C. B. Hellquist 05/381, cult. & coll. Z. Kaplan 1648 (Fig. 1b). – 1736: USA, Maine, Penobscot Co.:
ditch in peat bog 0.5 km N–NNW of crossroads of Essex Street and Forest Road 7 km W of Orono, 44°53'17"N,
68°47'18"W, alt. 36 m, 4 VIII 2005, coll. Z. Kaplan & C. B. Hellquist 05/461, cult. & coll. Z. Kaplan 1736. –
2140:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), distr. Ziminskiy: stream at bridge 0.8 km NW of Ignay,
8 km SSW of Batama, 53°47'46.5"N, 101°36'03.5"E, alt. 485 m, 20 VIII 2009, coll. V. Chepinoga & Z. Kaplan
09/366, cult. & coll. Z. Kaplan 2140.
This species of the morphologically defined P. pusillus agg. (Kaplan & Štěpánek 2003)
has a circumpolar distribution particularly in boreal and temperate regions throughout the
Northern Hemisphere. Our counts are in accordance with the previous records of 2n = 26
based on plants from Iceland (Löve & Löve 1956, as P. pusillus [sensu Hagström]), Swe-
den (Palmgren 1939, as P. pusillus [sensu Hagström]), Slovakia (Murín 1992), Japan
(Harada 1956, Takusagawa 1961, as P. pusillus [sensu Hagström]) and Canada (Taylor &
Mulligan 1968, Löve & Löve 1981). The karyotype of this species seems to be character-
ized by the presence of a pair of bigger chromosomes with satellites of the size of small
chromosomes, which were observed in samples 174, 930, 1160, 1648 and 1736. One chro-
mosome pair in samples 174, 930 and 1736 had conspicuous centromeres.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 427
Potamogeton berchtoldii Fieber s. l.
2n = 26
1603 &1605: USA, Massachusetts, Berkshire Co.: Berkshire Pond at Lanesborough, 42°30'28"N, 73°11'50"W,
alt. 301 m, 21 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1603 & 1605. – 1619: USA, Ver-
mont, WashingtonCo.: Curtis Pond 0.5 km NW of Maple Corner, Calais, 44°22'36"N, 72°30'03"W, alt. 371 m, 22
VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1819 (Fig. 1c). – 1708: USA, Maine,
Aroostook Co.: Nickerson Lake at south-eastern edge of New Limerick, Linneus Twp., 5 km WSW of Houlton,
46°05'32"N, 67°54'43"W, alt. 116 m, 2 VIII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1708.
2n = ca 26
1677: USA, Massachusetts, Franklin Co.: northern part of Lake Rohunta near Route 2, 1.5 km SE of Orange,
42°33'47"N, 72°16'23"W, alt. 162 m, 27 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan
428 Preslia 85: 421–482, 2013
Fig. 1. – Chromosomes (photograph of the cytological preparation onthe left with its interpretation on the right in
each pair) of selected species and hybrids of Potamogetonaceae at the metaphase of the first meiotic division of
the pollen mother cells (a) or at mitotic metaphase in somatic cells (b–o), arranged according to increasing chro-
mosome number: a–Potamogeton gramineus, sample 2072, n = 26; b–Potamogeton berchtoldii, sample 1648,
2n = 26; c–P. berchtoldii s. l., sample 1619, 2n = 26; d–P. foliosus, sample 1593, 2n = 26; e–P. pusillus, sample
1715, 2n = 26; f–P. trichoides, sample 1903, 2n = 26; g–P. acutifolius, sample 321, 2n = 28; h–P. cheesemanii,
sample 950, 2n = 28; i&j–P. compressus, sample 1962, 2n = 28; k–P. polygonifolius, sample 1535, 2n = 28;
l–P. spirillus, sample 1695, 2n = 28; m–P. zosteriformis, sample 1491, 2n = 28; n–P. pusillus, sample 1133,
2n = 39; o–P. ×gessnacensis, sample 1286, 2n = 40. Scale bar identical for all figures = 10 μm.
1677. – 1699: USA, Maine, Aroostook Co.: Nickerson Lake at south-eastern margin of New Limerick, Linneus
Twp., 5 km WSW of Houlton, 46°05'32"N, 67°54'43"W, alt. 116 m, 2 VIII 2005, coll. Z. Kaplan & C. B.
Hellquist, cult. & coll. Z. Kaplan 1699. – 1719: USA, Maine, Aroostook Co.: oxbow lake of Pettingrill Brook
1.5 km above its mouth in Aroostook River, just S of Route 164, Washburn, 6 km NNW of Presque Isle,
46°44'20"N, 68°01'59"W, alt. 130 m, 2 VIII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1719.
These plants from a relatively limited area in New England, USA, would be morpho-
logically identified as P. berchtoldii as currently understood, but they deviate slightly from
the typical widespread form of this species. Their exact taxonomic identity requires fur-
ther study. The karyotype of sample 1619 has a pair of bigger chromosomes with satellites
and a pair of chromosomes with conspicuous centromeres (Fig. 3b).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 429
Fig. 2. – Chromosomes (photograph of cytological preparation on the left with its interpretation on the right in
each pair) of selected species and hybrids of Potamogetonaceae at mitotic metaphase in somatic cells, arranged
according to increasing chromosome number: a–Potamogeton alpinus, sample 338, 2n = 52; b–P. gramineus,
sample 885, 2n = 52; c–P. maackianus, sample 1768, 2n = 52; d–P. natans, sample 977, 2n = 52;
e–P. perfoliatus, sample 985, 2n = 52; f–P. perfoliatus, sample 1002, 2n = 52; g–P. richardsonii, sample 1056,
2n = 52; h–P. ×nitens, sample 879, 2n = 52; i–P. ×undulatus, sample 1025, 2n = 52; j–P. ×lintonii, sample 2119,
2n = 65; k–P. ×salicifolius, sample 1017, 2n = 78; l–P. ×torssanderi, sample 1006, 2n = 78; m–Stuckenia
filiformis, sample 1187, 2n = 78; n–Potamogeton illinoensis, sample 856, 2n = 104; o–P. schweinfurthii, sample
861, 2n = 104. Scale bar identical for all figures = 10 μm.
430 Preslia 85: 421–482, 2013
Fig. 3. – Selected karyotypes with satellites (solid black arrows) and chromosomes with conspicuous centromeres
(hollow arrowheads): a–Potamogeton acutifolius, sample 321, 2n = 28; b–P. berchtoldii s. l., sample 1619, 2n = 26;
c–P. compressus, sample 1962, 2n = 28; d–P. foliosus, sample 1593, 2n = 26; e–P. pusillus, sample 1715, 2n = 26.
Potamogeton cheesemanii A. Benn.
2n = 28
950:N
EW ZEALAND, South Island, region Canterbury: small drain near Christchurch, III 1998, coll. A.-M.
Schwarz, cult. & coll. Z. Kaplan 950 (Fig. 1h). – 1070:N
EW ZEALAND, North Island, region Auckland: Lake Par-
kinson 7 km SW of Waiuku, 37°19'S, 174°41'E, 19 III 1999, coll. D. Hofstra, cult. & coll. Z. Kaplan 1070.
This species occurs in New Zealand, Australia and Tasmania. So far, only an approximate
count of 2n = ca 28 is published by De Lange et al. (2004) for plants from New Zealand.
Potamogeton clystocarpus Fernald
2n = ca 26
1671 &1672: USA, Texas, Jeff Davis Co.: Davis Mountains, Willow Canyon, Willow Creek, isolated pool in dry
creek bed, 30°52'13"N, 104°03'54"W, 2005, coll. C. B. Hellquist, cult. & coll. Z. Kaplan 1671 & 1672.
This species is a Texas endemic closely related to P. berchtoldii (Les et al. 2009, Kaplan
& Reveal 2013, and this study). The chromosome count published here is the first for this
species.
Potamogeton coloratus Hornem.
2n = 28
2252:C
ZECH REPUBLIC, distr. Nymburk: pool in E part of Hrabanovská černava National Nature Reserve 0.8 km
NNW of Lysá nad Labem, 50°13'03.8"N, 14°50'10.1"E, alt. 189 m, 23 VI 2010, coll. Z. Kaplan 10/171, cult. &
coll. Z. Kaplan 2252.
This species is distributed mainly in western, central and southern Europe, with a few
localities in south-western Asia and northernmost Africa. Two chromosome records were
published previously, n = 13 for Sweden by Palmgren (1939) and an approximate count of
2n = ca 26 for the British Isles by Hollingsworth et al. (1995a).
Potamogeton compressus L.
2n = 28
1012:S
WEDEN, prov. Uppland: northern edge of Sparren Lake near Smedsmora, 10 km ENE–E of Närtuna,
59°42'35"N, 18°21'10"E, alt. 17 m, 14 VIII 1998, coll. Z. Kaplan 98/350, cult. & coll. Z. Kaplan 1012. – 1922:
POLAND, Województwo Świętokrzyskie: small artificial pond in NW part of Starachowice near
Skarżysko-Kamienna, alt. 51°03'13.2"N, 21°02'38.2"E,alt. 203 m, 29 VII 2007, coll. J. Zalewska-Gałosz, cult. &
coll. Z. Kaplan 1922. – 1962:S
WEDEN, prov. Uppland, Stockholm county, municipality (kommun) of Norrtälje,
Vätö parish: Storträsket Lake 0.8 km S–SSW of Harg, 59°47'55.5"N, 18°57'06.2"E, alt. 4 m, 28 VIII 2008, coll.
Z. Kaplan & A. Svenson 08/633, cult. & coll. Z. Kaplan 1962 (Fig. 1i & j). – 2138:R
USSIA, Siberia, prov. Irkutsk
(Irkutskaya oblast’), distr. Alarskiy: water reservoir at north-north-eastern edge of Kutulik, 53°22'12.7"N,
102°46'48.1"E, alt. 514 m, 20 VIII 2009, coll. Z. Kaplan & V. Chepinoga 09/364, cult. & coll. Z. Kaplan 2138.
2n = 42
1022:D
ENMARK, Jylland (Jutland), region Midtjylland (Central Denmark Region): GudenåRiver below motor-
way bridge at west-south-western edge of Randers, 56°27'19"N, 9°59'30"E, alt. 1 m, 18 VIII 1998, coll.
Z. Kaplan 98/368, cult. & coll. Z. Kaplan 1022.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 431
This species occurs in boreal and temperate regions of Europe and Asia. Our diploid
counts agree with the records of Takusagawa (1961, as P. monoginus, n = 14, 2n = 28) for
Japan. Some variation (2n = 26, 28, 38–41) is reported by Harada (1956, as P. monoginus),
indicating that he also might have detected triploids. Our samples of other species of the
P. compressus group (sensu Kaplan & Marhold 2012) also have 2n = 28 (see under
P. acutifolius and P. zosteriformis), which indicates that this is the main chromosome num-
ber for the entire group. In contrast, the early study by Palmgren (1939) gave n = 13 for
Sweden and Probatova et al. (2008a) and Chepinoga et al. (2012) recently recorded 2n =
26 for Russia. Another record of 2n = 26 for Canada by Löve & Löve (1981) is erroneous
because P. compressus does not occur in North America and the count was presumably
made on another taxon (see also discussion under P. zosteriformis).
The karyotype of P. compressus includes a pair of bigger chromosomes with satellites
(Figs 1i & 3c). The triploid count was determined in a single sample. The plant was sterile,
but neither morphology nor DNA sequences (nuclear and plastid markers) indicated any
vestige of hybridization with another species. We therefore interpret this plant as an
autotriploid. For a similar sporadic occurrence of a sterile autotriploid individual within
a fertile diploid species, see the discussion under P. pusillus.
Potamogeton crispus L.
2n = 52
2077:C
ZECH REPUBLIC, distr. Hradec Králové: Horní Flajšar fishpond 0.5 km SW of Štít, 50°06'43.5"N,
15°28'20.6"E, alt. 218 m, 8 VI 2009, coll. Z. Kaplan 09/153.
2n = ca 52
2339:S
OUTH KOREA, prov. Gyeongsangbuk-do (North Gyeongsang): NakdongRiver (Nakdongang) 1.5 km E of
Buncheon, 36°44'06"N, 128°51'54"E, 26 IX 2010, coll. P. Petřík, cult. & coll. Z. Kaplan 2339.
Our chromosome counts for this widely distributed species correspond with the most
frequent literature records. The same numbers are reported for Sweden by Palmgren
(1939, as n = 26), for Germany by Scheerer (1939, as 2n = ca 52), for Poland by Jankun (in
Pogan et al. 1983), for Slovakia by Uhríková (in Májovský et al. 1978) and Hindáková &
Schwarzová (1980), for India by Sharma & Chatterjee (1967), Bhattacharya & Ghosh
(1978) and Ghosh & Bhattacharya (1980), for China by Wan et al.(2012) and for Japan by
Harada (1942) and Takusagawa (1961). Different counts are rarely reported: n = 13, 2n =
26 by Bhattacharya & Ghosh (1978) and Ghosh & Bhattacharya (1980), 2n = 48 by Wan et
al. (2012), 2n = 50 by Misra (1972), 2n = 56 by Nakata & Nagai (1998) and 2n = 78 by
Sharma & Chatterjee (1967). In the context of the 13 records of 2n = 52 cited above, the
other numbers are discounted unless they are confirmed and clearly documented by other
studies.
Potamogeton distinctus A. Benn.
2n = ca 52
1916:J
APAN, Honshu, Niigata Prefecture(Niigata-ken), Muramatsu: Kalibane, 8 IX 2005, coll. N. Tanaka, cult. &
coll. Z. Kaplan 1916.
432 Preslia 85: 421–482, 2013
This species is closely related to the widespread P. nodosus (Wiegleb 1990a, Wiegleb
& Kaplan 1998, this study). It occurs in eastern and southeastern Asia, on Pacific islands
and in northern Australia. Our observation is consistent with previous counts for Japan by
Harada (1942, as 2n = 52) and Takusagawa (1961, as n = 26, 2n = 52) and for China by
Wan et al. (2012). A slightly different and apparently erroneous count of n = 28 is reported
in an early study by Takusagawa (1939). Wan et al. (2012) report “one cell with 2n = 26” in
an individual with 2n = 52. We consider this observation to be an artefact, apparently
based on an incomplete karyotype produced during preparation for FISH.
Potamogeton epihydrus Raf.
2n = ca 26
1040: USA, Maine, Penobscot Co.: Harrington Cove, Pushaw Lake, Orono, 16 VII 1998, coll. C. B. Hellquist,
cult. & coll. Z. Kaplan 1040.
The core of the distribution of this amphiatlantic species is in North America north of
Mexico, with an isolated occurrence located in north-western Europe in the British Isles.
The same chromosome number as here was recorded also from other states in the USA: for
Colorado by Löve et al. (1971) and Wisconsin by Parfitt & Harriman (1981, as n = 13), as
well as for Canada: for Manitoba by Löve & Löve (1981), Quebec by Löve & Löve (1982)
and for two populations on Queen Charlotte Islands, British Columbia by Taylor & Mulli-
gan (1968).
Potamogeton foliosus Raf.
2n = 26
1043: USA, Maine, Aroostook Co.: pond on west side of Presque Isle airport by dump, Presque Isle, 14 VII 1998,
coll. C. B. Hellquist 16293, cult. & coll. Z. Kaplan 1043. – 1044: USA, Vermont, Orleans Co.: Lake Parker, West
Glover, 21 VII 1998,coll. C. B. Hellquist & R. G. Popp 16326, cult. & coll. Z. Kaplan 1044. – 1593: USA, Massa-
chusetts, Berkshire Co.: pond on Kinderhook Creek at crossroads of Route 43 and Whitman Road in Hancock,
42°34'40"N, 73°17'51"W, alt. 385 m, 21 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1593
(Fig. 1d). – 1621: USA, Vermont, Orleans Co.: Lake Parker 1 km WSW of West Glover, 44°43'34"N,
72°13'53"W, alt. 396 m, 22 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1621. – 1668:
USA, Vermont, Rutland Co.: NE corner of Lake Hortonia 2.5 km NE of Hortonia, Sudbury, 43°45'09"N,
73°12'38"W, alt. 148 m, 25 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1668.
The chromosome number of this North and Central American species has long been
controversial. Two counts were published corresponding to the diploid level, 2n = 26 for
Manitoba, Canada (Löve & Löve 1981) and 2n = 28 for Minnesota, USA (Stern 1961).
The latter may have resulted from the misinterpretation of two satellites that are present in
our samples (Fig. 3d). An unusually low number of n = 7 (with some cells n = 8) appeared
in an early study by Wiegand (1899). This count requires special attention because it is dis-
cussed in the literature as a potential base chromosome number of the family. However,
Wiegand’s own figures show chromosomes that are too large to belong to Potamogeton
and it is therefore likely that he used misidentified material. This controversial count has
never been confirmed. We therefore consider Wiegand’s anomalous count as erroneous
(see also general discussion below).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 433
Potamogeton friesii Rupr.
2n = 26
1658: USA, Vermont, Rutland Co.: Burr Pond 2.5 km SSE of Hyde Manor, Sudbury, 43°46'06"N, 73°10'57"W,
alt. 157 m, 25 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1658. – 1949:A
USTRIA,
Oberösterreich: western edge of Traunsee Lake at Altmünster, 1.5 km SW of Gmunden, 47°54'06.1"N,
13°46'11.2"E, alt. 422 m, 9 VIII 2008, coll. Z. Kaplan 08/606, cult. & coll. Z. Kaplan 1949.
Our counts established on this circumpolar species are the same as two previous
records, one for Sweden (Palmgren 1939) and the other for Canada (Löve & Löve 1981).
Potamogeton ‘gayi’ auct. hort., non A. Benn.
2n = 26
1194: Original locality unknown, plant samples from the Botanical Garden ofthe University of Wrocław, Poland,
provided by R. Kamiński in 2000, cult. & coll. Z. Kaplan 1194.
Proper P. gayi A. Benn. occurs in South America. Plants designated with this name are
sometimes grown in aquaria and in water tanks in greenhouses. The garden plant that we
used for chromosome counting was also so named. Our record is the first chromosome
count for this cultivated taxon. The sample studied differs slightly morphologically from
typical natural plants, is consistently sterile, and DNA sequencing indicates its hybrid ori-
gin (J. Fehrer & Z. Kaplan, unpublished data). The exact identity of these aquarium plants
and their comparison with samples from natural populations of P. gayi and of similar taxa
in South America require further study. The chromosome count of proper P. gayi from the
field has yet to be determined.
Potamogeton gemmiparus (J. W. Robbins) Morong
2n = 26
1721: USA, Maine, Hancock Co.: SE shore of Graham Lake 3 km NNE of Ellsworth, 44°35'36"N, 68°24'40"W,
alt. 31 m, 3 VIII 2005, coll. Z. Kaplan & C. B. Hellquist 05/445, cult. & coll. Z. Kaplan 1721.
This is the first chromosome count for this species, which is confined to a relatively
small area in northeastern USA and adjacent southeastern Canada.
Potamogeton gramineus L.
n = 26
2072:C
ZECH REPUBLIC, distr. Hradec Králové: Dolní Flajšar fishpond 0.6 km WSW of Štít, 50°06'50.6"N,
15°28'02.5"E, alt. 216 m, 23 V 2009, coll. Z. Kaplan 09/54 (Fig. 1a).
2n = 52
885:C
ZECH REPUBLIC, distr. Náchod: eastern edge of Rozkoš Reservoir by Šeřeč, 50°23'02"N, 16°05'14"E, alt.
280 m, 22 VIII 1997, coll. Z. Kaplan 97/829, cult. & coll. Z. Kaplan 885 (Fig. 2b). – 897:C
ZECH REPUBLIC, distr.
Česká Lípa: Držník fishpond in forest 1.1 km ESE of Hradčany, 4 km S of Mimoň, 50°36'37"N, 14°43'23"E, alt.
273 m, 18 IX 1996, coll. Z. Kaplan 96/638, cult. & coll. Z. Kaplan 897. – 1156:F
RANCE, Bretagne, Morbihan,
Lorient: Scorff River ca 30 km from its mouth, VI 1998, coll. J. Květ, cult. & coll. Z. Kaplan 1156. – 1285:
FRANCE, Lorraine, Moselle: Saarkohlenkanal at Rémelfing, ca 49°05'25"N, 07°05'55"E, alt. 200 m, 21 July 2001,
coll. P. Wolff, cult. & coll. Z. Kaplan 1285. – 2240:G
REECE, region (periphery) of Epirus (Ípiros), Thesprotía
434 Preslia 85: 421–482, 2013
Pref.: northern edge of Limni Prontani (Lake Prontani) 2 km NNW of Ampelia, 39°26'55"N, 20°25'20"E, alt. 240
m, 10 VI 2010, coll. Z. Kaplan 10/146, cult. & coll. Z. Kaplan 2240.
This species has an extensive circumpolar range in boreal and temperate regions
throughout the Northern Hemisphere and appears to be invariable in chromosome number.
Our counts are consistent with the cytotype 2n = 52 previously recorded for Sweden
(Palmgren 1939, as n = 26), Iceland (Löve & Löve 1956), Russia (Probatova et al. 2008a),
China (Wan et al. 2012), Japan (Harada 1956), Canada (Taylor & Mulligan 1968, as n =
26, Löve & Löve 1981) and USA (Stern 1961, as n = 26, Pringle 1969).
Potamogeton groenlandicus Hagstr.
2n = 26
1153:G
REENLAND, Disko Fjord: lakes between Eqalunguit and Kangerdluarssuk, 69°31'13.5"N, 53°43'36.5"W,
29–30 VII 1999, coll. F. Rune & S. Bernstein, cult. & coll. Z. Kaplan 1153.
This is a relatively little-known taxon whose present concept includes all linear-leaved
plants similar to the P. pusillus agg. (sensu Kaplan & Štěpánek 2003) that occur in Green-
land. Our karyological observations confirm two previously published records 2n = 26
(Jörgensen et al. 1958, Dalgaard 1989). DNA sequencing indicates that the sample ana-
lysed is apparently a hybrid between P. berchtoldii and P. sibiricus (see below). Conse-
quently, P. sibiricus, for which no counts are available as yet, should have the same chro-
mosome number. The present concept of P. groenlandicus may change in future taxo-
nomic revisions.
Potamogeton hillii Morong
2n = 26
1607: USA, Vermont, Washington Co.: Bliss Pond 2.5 km N of Adamant, Calais, 44°21'04"N, 72°30'05"W, alt.
369 m, 22 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/349, cult. & coll. Z. Kaplan 1607.
This is the first chromosome record for this species whose distribution is scattered in
north-eastern USA and adjacent Canada.
Potamogeton illinoensis Morong
2n = 104
856:A
RGENTINA, prov. Río Negro: main irrigation system at Viedma, ca 40°48'S, 63°07'W, provided by P. Denny
in 1997, cult. & coll. Z. Kaplan 856 (Fig. 2n).
This species occurs in North and South America from southern Canada in the north
through Mexico and the West Indies southwards to northern Argentina. The two chromo-
some records published so far, for Manitoba, Canada (Löve & Löve 1981) and Minnesota,
USA (Stern 1961, as n = 52), both correspond to our count of 2n = 104. So far, the
octoploid level has been recorded in Potamogeton only for this species. Our record is the
first count determined on a South American plant of P. illinoensis.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 435
Potamogeton lucens L.
2n = 52
858:T
HE NETHERLANDS, prov. Limburg: Arcen, ca 51°28'N, 06°12'E,coll. P. Denny, cult. & coll. Z. Kaplan 858. –
912:C
ZECH REPUBLIC, distr. Mladá Boleslav, region of Český ráj: fishpond at west-south-western edge of
Arnoštice near Žehrov, 50°31'42.8"N, 15°05'11.2"E, 247 m, 18 IX 1997, coll. Z. Kaplan 97/914, cult. & coll.
Z. Kaplan 912. – 1762:J
APAN, Honshu, Chiba Prefecture(Chiba-ken): Tegagawa (Tega River) NE of Tokyo, alt. 1
m, 2006, coll. N. Tanaka,cult. & coll. Z. Kaplan 1762. – 2135:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’),
border of Alarskiy & Cheremkhovskiy distr.: Golumet’ River at bridge 2.2 km SW of Nygda, 11 km SE of Alar’,
52°59'36.4"N, 102°40'01.3"E, alt. 445 m, 19 VIII 2009, coll. Z. Kaplan & V. Chepinoga 09/361, cult. & coll.
Z. Kaplan 2135.
This species occurs in Europe, Asia and rarely also in northern and eastern Africa. Our
counts correspond to records published for Sweden (Palmgren 1939, as n = 26), Slovakia
(Uhríková in Májovský et al. 1978), Russia (Probatova et al. 2008a), China (Wan et al.
2012) and Japan (Harada 1942, Takusagawa 1961, both as P. dentatus).
Potamogeton maackianus A. Benn.
2n = 52
1570:C
HINA, prov. Hubei: Xiliang Lake NW of Xianning, 29°55'N, 114°05'E, 2000, coll. W. Li, cult. & coll.
Z. Kaplan 1570. – 1768:J
APAN, Honshu, Kanagawa Prefecture (Kanagawa-ken): Ashino-ko Lake, 2006, coll. N.
Tanaka,cult. & coll. Z. Kaplan 1768 (Fig. 2c). – 2020:C
HINA, prov. Heilongjiang, Mishan county: pond, IX 2008,
coll. X.-L. Zhang, cult. & coll. Z. Kaplan 2020.
Our chromosome counts for this species of eastern and south-eastern Asia agree with
the literature records for Japan by Harada (1942) and Takusagawa (1961). The count 2n =
26 for the Russian Far East reported by Probatova & Sokolovskaya (1984) is considered
erroneous, and 2n = 56 for Japan by Uchiyama (1989) is also doubtful (see also general
discussion below).
Potamogeton natans L.
2n = 52
977:S
WITZERLAND, canton Sankt Gallen: ditch with running water 200 m SSW of Altenrhein near Rorschach,
47°29'08.3"N, 09°32'56.4"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan 98/122, cult. & coll. Z. Kaplan 977 (Fig.
2d). – 1890:C
ZECH REPUBLIC, distr. České Budějovice: side pool of Stropnice stream 640 m NE of Třebeč,
48°52'41.4"N, 14°41'16.8"E, alt. 450 m, 29 VI 2007, coll. Z. Kaplan 07/215, cult. & coll. Z. Kaplan 1890.
This species is widespread in circumpolar, boreal and temperate regions of the North-
ern Hemisphere. The chromosome numbers presented here are in accordance with the
most frequently recorded cytotype previously reported for Sweden (Palmgren 1939, as n =
26), Iceland (Löve & Löve 1956), British Isles (Hollingsworth et al. 1995b, as 2n = ca 52),
Poland (Pogan in Skalińska et al. 1966), Slovakia (Murín in Májovský et al. 1976), China
(Wan et al. 2012), Japan (Harada 1942, Takusagawa 1961) and Canada (Löve & Löve
1981). Another cytotype corresponding to 2n = 42 is recorded for the USA (Stern 1961, as
n = 21) and the Russian Far East (Probatova & Sokolovskaya 1984, as 2n = ca 42). In light
of the 12 observations of 2n = 52 we consider the two lower counts as erroneous. This view
is also supported by the fact that all our samples of the respective group of broad-leaved
436 Preslia 85: 421–482, 2013
species invariably have 2n = 52 (see also the discussion below on the pattern in the varia-
tion in the chromosome numbers).
Potamogeton nodosus Poir. [syn.: P. fluitans auct.]
2n = 52
2251:G
REECE, region (periphery) of Epirus (Ípiros), Préveza Pref.: shallow southern edge of Limni Zirós (Lake
Ziros) 1.5 km N–NNW of Romia, 39°14'07"N, 20°50'45"E, alt. 53 m, 13 VI 2010, coll. Z. Kaplan 10/165.
Our count for this subcosmopolitan species is in accordance with the records (appar-
ently for Poland) by Kuleszanka (1934, as P. fluitans, n = 26), Italy by Ottonello et al.
(1985), Morocco by Talavera & García Murillo (1992, as P. fluitans, as n = 26), India by
Sivakamasundari & Selvaraj (1999), China by Wan et al. (2012) and Canada by Taylor &
Mulligan (1968, as n = 26). Some of the records given for India under the name P. indicus
may also refer to P. nodosus, e.g. the record 2n = 52 by Ghosh & Bhattacharya (1980).
Only recently Wan et al. (2012) report for China also 2n = 48 and “one cell with 2n = 24” in
an individual with 2n = 52. We consider these observations to be artefacts based on prepa-
rations for FISH.
Potamogeton obtusifolius Mert. et W. D. J. Koch
2n = 26
1138:C
ZECH REPUBLIC, distr. Nový Jičín: Kotvice fishpond 1–1.5 km SE of railway station in Studénka,
49°41'58"N, 18°04'52"E, alt. 232 m, 9 VII 1999, coll. Z. Kaplan 99/126, cult. & coll. Z. Kaplan 1138.
2n = ca 26
1051:C
ANADA, Manitoba: Snow Creek at west end of Snow Lake, town of Snow Lake, 60 mi. ENE of Cranberry
Portage, 20 VIII 1998, coll. C. B. Hellquist & C. E. Hellquist 16369, cult. & coll. Z. Kaplan 1051. – 2075:C
ZECH
REPUBLIC, distr. Hradec Králové: Dolní Flajšar fishpond 0.6 km WSW of Štít, 50°06'50.6"N, 15°28'02.5"E, alt.
216 m, 23 V 2009, coll. Z. Kaplan 09/59, cult. & coll. Z. Kaplan 2075.
This species is circumpolar, distributed in Europe, western and northern Asia and in
northern North America. So far, there is only one chromosome count of 2n = 26 for this
species, published for Sweden by Palmgren (1939).
Potamogeton ochreatus Raoul
2n = 26
1071:N
EW ZEALAND, North Island, region Bay of Plenty: Lake MacLaren SW of Tauranga, ca 37°49'S, 176°02'E,
19 III 1999, coll. D. Hofstra, cult. & coll. Z. Kaplan 1071.
2n = ca 26
1072:N
EW ZEALAND, North Island, region Waikato:Lake Rotoaira 9 km SW of Turangi, 39°03'S, 175°43'E, 23 III
1999, coll. D. Hofstra, cult. & coll. Z. Kaplan 1072.
This species is endemic to south-western and south-eastern Australia, New Zealand
and a few surrounding Pacific islands. The chromosome counts presented here are the first
records for this species.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 437
Potamogeton octandrus Poir.
2n = 28
1915:J
APAN, Honshu, Aomori Prefecture (Aomori-ken): Nakazato, Pond Osawauchi, 30 VIII 2006, coll. N.
Tanaka, cult. & coll. Z. Kaplan 1915.
This species exhibits a disjunct distribution in central and southern Africa, southern
and eastern Asia and Australia. Our count is the same as all previously published records:
for Japan published by Harada (1956, as P. numasakianus), Takusagawa (1961, as
P. numasakianus), Uchiyama (1989) and Nakata & Nagai (1998) and for China by Wan et
al. (2012).
Harada (1942) and Takusagawa (1961) record 2n = 28 for Japan under the name
P. vaseyi. Later revisions showed that P. vaseyi does not occur in Japan (Kadono 1982, Ka
1984, Wiegleb & Kaplan 1998) and that this name was misapplied to plants of
P. octandrus. This is probably also the actual identity of plants on which the records pub-
lished for P. vaseyi were determined. The species P. vaseyi is confined to North America
(Wiegleb & Kaplan 1998) and its chromosome number has not been determined yet.
Potamogeton oxyphyllus Miq.
2n = 26
1765:J
APAN, Honshu, Fukushima Prefecture (Fukushima-ken), 2006, coll. N. Tanaka, cult. & coll. Z. Kaplan
1762.
This species occurs in eastern and south-eastern Asia. The same chromosome number
as we identified is recorded for Japan by Harada (1942) and Takusagawa (1961).
Uchiyama (1989) records 2n = 28 for this species.
Potamogeton perfoliatus L.
2n = 52
840:C
ZECH REPUBLIC, distr. Uherské Hradiště: lake in sand pit 2.1 km NW of railway station in Ostrožská Nová
Ves, 49°00'58"N, 17°25'36"E, alt. 173 m, 25 VI 1997, coll. Z. Kaplan 97/524, cult. & coll. Z. Kaplan 840. – 979:
SWITZERLAND, canton Sankt Gallen: southern edge of Bodensee (Lake Constance) 0.8 km N–NNE of Altenrhein
near Rorschach, 47°30'03"N, 09°33'18"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan 98/125, cult. & coll. Z. Kaplan
979. – 985:A
USTRIA, Vorarlberg, Bregenz: southern edge of Fussacher Bucht (bay) of Bodensee (Lake Con-
stance) 1.5 km N–NNE of Fußach, 47°29'43"N, 09°40'06"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan 98/131, cult.
& coll. Z. Kaplan 985 (Fig. 2e). – 1002:S
WEDEN, prov. Skåne: Björkaån River 0.5 km ENE of church in Björka,
4 km WNW of Sjöbo, 55°39'28"N, 13°38'35"E, alt. 24 m, 12 VIII 1998, coll. Z. Kaplan 98/338, cult. & coll.
Z. Kaplan 1002 (Fig. 2f). – 1470 & 1471:G
ERMANY, Bavaria: small backwater at Main River 1.2 km ENE of
Ebing, ca 50°02'N, 10°55'E, 11 VI 2003, coll. L. Meierott, cult. & coll. Z. Kaplan 1470 & 1471. – 1531:I
TALY,
Trentino-Alto Adige, prov. Bolzano: Lake Muta (Lago di Muta, Haider See) S of San Valentino alla Muta,
46°44'53"N, 10°32'01"E, 8 VI 2004, coll. Z. Kaplan & J. Štěpánková 04/63, cult. & coll. Z. Kaplan 1531.
This species occurs in Europe, northern and central Africa, Asia, Australia, eastern
North America and Central America. In addition to our seven counts for six countries
there are 11 identical records for Iceland (Löve & Löve 1956), British Isles
(Hollingsworth et al. 1998, as 2n = ca 52), Sweden (Palmgren 1939, as n = 26), Germany
(Scheerer 1939, as 2n = ca 52), Slovakia (Váchová & Feráková 1986, Váchová in
Májovský et al. 1987), Hungary (Felföldy 1947, as n = 26), an unspecified record for
438 Preslia 85: 421–482, 2013
Europe (Löve 1954b), China (Guo in Du et al. 2009, Wan et al. 2012) and Japan (Harada
1942, Takusagawa 1961).
Besides these 11 tetraploid records, different chromosome numbers are reported in the
literature: n = 7 is recorded by Takusagawa (1939) for Japan, 2n = 26 by Löve (1954a, b, as
P. bupleuroides) for North America and by Probatova & Sokolovskaya (1984) and
Probatova et al. (2008b) for the Russian Far East, 2n = ca 40 by Probatova &
Sokolovskaya (1984) for Russia, n = ca 24 by Wiśniewska (1931) for Poland, and 2n = 78
by Arohonka (1982) for Finland and by Probatova & Sokolovskaya (1986) for the Russian
Far East. It is the goal of further studies to show whether these deviant chromosome counts
reflect real variation in chromosome number of P. perfoliatus or whether they are errone-
ous. In any case it should be noted that they all came from only five authors (or author
teams) who either conducted only a single count in this family or published highly doubt-
ful or even demonstrably erroneous counts for other species as well. These few controver-
sial records for P. perfoliatus contrast to 18 tetraploid counts of 2n = 52 for 13 different
countries. We are sceptical that these deviant counts are correct. Taken together with the
placement of this species in phylogenetic analysis (see the general discussion below), we
discount all counts below the tetraploid level. The extremely low count of n = 7 given by
Takusagawa (1939) is particularly incredible. On the dubious records in the 1954 papers
by Löve, see the discussion under P. zosteriformis.
Potamogeton polygonifolius Pourr. [syn.: P. oblongus Viv.]
2n = 28
1533:C
ZECH REPUBLIC, distr. Cheb: Nový fishpond0.3 km WNW of Studánka railway station by Novosedly near
Hranice, 50°16'35"N, 12°10'24"E, alt. 610 m, 13 VII 2004, coll. Z. Kaplan 04/168. – 1534:C
ZECH REPUBLIC,
distr. Cheb: small pool in peat bog 0.7 km SSW of Pastviny, 4.9 km W–WSW of Studánka railway station by
Novosedly near Hranice, 50°16'09"N, 12°08'45"E, alt. 605 m, 13 VII 2004, coll. Z. Kaplan 04/172. – 1535:
CZECH REPUBLIC, distr. Cheb: small pool at NE bank of Vodárenská nádrž reservoir 1.4 km NNW–NW of
Studánka railway station by Novosedly near Hranice, 50°17'14"N, 12°09'57"E, alt. 585 m, 13 VII 2004, coll.
Z. Kaplan 04/173 (Fig. 1k).
Potamogeton polygonifolius is a species with an amphiatlantic distribution. It occurs in
western, northern, central and southern Europe, on the Azores, Madeira, and rarely also in
limited areas of northernmost Africa and easternmost North America. The literature
reports two similar chromosome numbers for this species: 2n = 26 (Palmgren 1939, as n =
13, for Sweden; Fernandes 1950 for Portugal; and Ficini et al. 1980, as P. oblongus, for
Italy) and 2n = 28 (Hollingsworth et al. 1998 for three localities in the British Isles).
Hollingsworth et al. (1998) published their new chromosome counts based on careful
examination of plants from three different populations from England. The authors com-
mented that although they experienced difficulties in chromosome counting of other
Potamogeton taxa, for their samples of P. polygonifolius clear metaphase preparations
were achieved and all unambiguously gave a count of 2n = 28 (see also Preston et al.
1998). To establish the chromosome number for the Czech plants, we therefore intention-
ally sampled three populations thoroughly and studied carefully altogether more than 40
root tips from different plants to correctly distinguish between the 26 and 28 chromosomes
recorded for this species in the literature. We came to unequivocal counts of 2n = 28 in at
least 20 well-spread mitotic preparations from 12 different root tips from the three popula-
Kaplan et al.: Chromosome numbers of Potamogetonaceae 439
tions. Thus the Czech plants agree in their chromosome number with British counts for
this species. This number is also indirectly confirmed by P. ×gessnacensis, a hybrid with
P. natans, and by P. ×rivularis, a hybrid with P. berchtoldii (see below). The other three
published counts of 2n = 26 are therefore interpreted here as only approximate counts,
potentially influenced by the mistaken belief in the earlier literature, that all Potamogeton
diploids have 2n = 26.
An additional chromosome number recorded for this species comes from Spain,
although it was not published under the name P. polygonifolius. First, Löve & Kjellqvist
(1973) published a diploid count of 2n = 26 under the name P. alpinus. This was rather sur-
prising as all previous records for this species are tetraploid, with 2n = 52 (see above). This
record was “corrected” in a subsequent paper that claimed the count was actually 2n = 52
(Löve & Kjellqvist 1974). This “correction” was apparently motivated by an unfortunate
effort to fit the new record from Spain to other records published for this species. We have
examined the herbarium specimen A. Löve & E. Kjellqvist 512 preserved at LD, which is
the voucher for the above chromosome count(s) for P. alpinus. However, this specimen is
undoubtedly P. polygonifolius. The original herbarium label attached to the voucher
clearly documents that “2n = 26” was indeed the chromosome number actually deter-
mined on this specimen. Not 2n = 52, but 2n = 26 was therefore the originalcount, the only
one established on this material. Although inexact, it is at least in accordance with the dip-
loid level known for P. polygonifolius.
In his summary of chromosome counts, Les (1983) treated P. oblongus with 2n = 26 as
a separate species from P. polygonifolius, for which he claimed 2n = 52. As demonstrated
by Preston et al. (1998) and Hollingsworth et al. (1998), the record 2n = 52 claimed for
P. polygonifolius is erroneous. The only primary record that could be traced was that
attributed to Takusagawa (1961) by Moore (1973). However, this count was never made,
but was merely the chromosome number expected by Takusagawa for this species on the
basis of the chromosome number of similar species (Preston et al. 1998, Hollingsworth et
al. 1998). It should also be noted that P. polygonifolius does not occur in eastern Asia and
that the names “P. oblongus” and “P. polygonifolius” were in Japan widely misapplied to
P. distinctus, which is indeed tetraploid.
On the incorrect assumption of the karyological differentiation, Crow & Hellquist
(2000) separated American populations under the name P. oblongus from “the closely
related P. polygonifolius of Europe, which is tetraploid”. As described above, the Euro-
pean populations of P. polygonifolius are diploid. Furthermore, the choice of the name
adopted for the American plants was incorrect, because P. oblongus was the name given to
plants described from north-western Italy. If the classification suggested by Crow &
Hellquist was correct, P. oblongus would become a synonym of P. polygonifolius and not
the correct name for the American populations. The separate taxonomic position of North
American plants was based solely on erroneous reports of chromosome numbers, as there
are no morphological differences. In addition, ITS sequences of American samples from
Newfoundland, the western margin of the distribution area of that species, are identical to
European material from Portugal and Denmark (J. Fehrer et al., unpublished data). We
therefore consider P. oblongus as conspecific with P. polygonifolius from Europe, north-
ern Africa and the Atlantic islands.
440 Preslia 85: 421–482, 2013
Potamogeton praelongus Wulfen
2n = 52
881: Germany, Mecklenburg-Vorpommern, Güstrow: Lake Gültz (Gültzsee) 2.2 km SSW of Dobbin,
53°35'23"N, 12°19'04"E, 15 VIII 1997, coll. Z. Kaplan 97/824, cult. & coll. Z. Kaplan 881.
Our count corresponds to the only chromosome number recorded for this circumboreal
species distributed throughout the Northern Hemisphere. The same karyotype is reported
for Sweden by Palmgren (1939, as n = 26), for Iceland by Löve & Löve (1956), for Japan
by Harada (1942) and Takusagawa (1961), and for Canada by Löve & Löve (1981).
Potamogeton pusillus L. s. str. [syn.: P. panormitanus Biv.]
2n = 26
307:C
ZECH REPUBLIC, distr. Jindřichův Hradec: Šimanov pond near Třeboň town, 1.4 km NE of Třeboň railway
station, 49°01'27"N, 14°46'41"E, alt. 428 m, 21 VIII 1996, coll. Z. Kaplan, cult. & coll. Z. Kaplan 307. – 959:
CZECH REPUBLIC, distr. Litoměřice: small pond in valley at northern edge of Pokratice suburb of Litoměřice,
50°33'18"N, 14°07'43"E, alt. 260 m, 27 V 1998, coll. Z. Kaplan 98/52, cult. & coll. Z. Kaplan 959. – 987/2:
AUSTRIA, Voralberg, Bregenz: southern edge of Fussacher Bucht (bay) of Bodensee (Lake Constance) 1.5 km
N–NNE of Fußach, 47°29'43"N, 09°40'06"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan, cult. & coll. Z. Kaplan
987/2. – 1159:C
ZECH REPUBLIC, distr. Jindřichův Hradec: Velký Panenský fishpond 1.3 km SSE of Lomnice nad
Lužnicí, 49°04'09"N, 14°43'50"E, alt. 420 m, 8 IX 1999, coll. Z. Kaplan, cult. & coll. Z. Kaplan 1159. – 1212:
CZECH REPUBLIC, distr. Jindřichův Hradec: Velký Dubovec pond 1.3 km SSE of Lomnice nad Lužnicí,
49°04'06"N, 14°43'19"E, alt. 425 m, 15 VI 2000, coll. Z. Kaplan 00/57, cult. & coll. Z. Kaplan 1212. – 1601:
USA, Massachusetts, Berkshire Co.: Berkshire Pond at Lanesborough, 42°30'28"N, 73°11'50"W, alt. 301 m, 21
VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1601. – 1712 & 1714 & 1715: USA, Maine,
Aroostook Co.: pond on Prestile Stream in Mars Hill, at crossroads of Routes 1 and 1A, 46°31'06"N, 67°52'01"W,
alt. 125 m, 2 VIII 2005, coll. Z. Kaplan & C. B. Hellquist 05/437 & 05/439 & 05/440, cult. & coll. Z. Kaplan 1712
& 1714 & 1715 (Fig. 1e). – 2076:C
ZECH REPUBLIC, distr. Hradec Králové:Dolní Flajšar fishpond 0.6 km WSW of
Štít, 50°06'50.6"N, 15°28'02.5"E, alt. 216 m, 23 V 2009, coll. Z. Kaplan 09/60.
2n = 39
1133:C
ZECH REPUBLIC, distr. Jičín: Rokytňanský rybník fishpond 0.4 km W of Dolní Rokytňany, 50°22'34,4"N,
15°07'13,7"E, alt. 234 m, 11 VI 1999, coll. Z. Kaplan 99/69, cult. & coll. Z. Kaplan 1133 (Fig. 1n).
The taxonomic delimitation of this species followed here is the narrow concept estab-
lished by Hagström (1916, as P. panormitanus), developed by Dandy & Taylor (1938),
and adopted e.g. by Dandy (1980), Preston (1995), Kaplan & Štěpánek (2003) and Kaplan
(2010b). This species is distributed in Europe, Africa, Asia and North America. Particu-
larly Scandinavian and Japanese botanists long followed the nomenclature established by
Hagström (1916). Their chromosome records for P. pusillus are therefore referable to
P. berchtoldii (see under this species).
The chromosome number 2n = 26 established for plants from the nine above-cited fer-
tile populations is consistent with the most frequently reported count. This was previously
recorded for Sweden (Palmgren 1939, as P. panormitanus), Slovakia (Mičieta in
Májovský et al. 2000), Morocco (Talavera & García Murillo 1992, as n = 13), China (Wan
et al. 2012) and Japan (Harada 1956, Takusagawa 1961, both as P. panormitanus).
A slightly different count of 2n = 28 was claimed for Japan by Harada (1942, as
P. panormitanus). This may have been caused by misinterpretation of two conspicuous
satellites that we observed in samples 1159, 1601 and 1715 (Fig. 3e) or of chromosomes
with conspicuous centromeres that we detected in sample 1715 (Fig. 3e). In light of alto-
Kaplan et al.: Chromosome numbers of Potamogetonaceae 441
gether 15 records of 2n = 26 cited above, we consider this count to be the only correct dip-
loid chromosome number for P. pusillus.
A different chromosome number is recorded for sample 1133. We repeated the sam-
pling three times (each count was made on several reliable mitotic plates) to be absolutely
sure of the chromosome number. We arrived at an unambiguous count of 2n = 39 (Fig. 1n).
No triploid plants of P. pusillus have been recorded so far. Sample 1133 was totally sterile.
Although it flowered freely and produced abundant spikes each season during eight years
of cultivaton, it failed to produce a single fruit and persisted only vegetatively. The whole
spikes rotted soon after flowering instead of setting fruit. In contrast, 16 other P. pusillus
samples cultivated under the same conditions, 9 of which were identified as diploid (see
the list above), regularly set well-formed and viable fruit.
The development of the flowers of sample 1133 was similar to that of sterile hybrids
(see Preston 1995:46, Preston et al. 1998, Kaplan & Wolff 2004, Kaplan & Fehrer 2004).
However, no sign of hybridization was observed in this sample. The plant was morpholog-
ically typical P. pusillus s. str. and all diagnostic features indicated this species. Isozyme
phenotypes were found to be species-specific in the P. pusillus agg. (Kaplan & Štěpánek
2003) and can be used to identify hybrids (e.g. Hollingsworth et al. 1995b, Preston et al.
1998, Kaplan et al. 2002, Kaplan & Wolff 2004, Kaplan 2007). However, the isozyme pat-
tern of sample 1133 corresponded to pure P. pusillus and no bands indicating hybridiza-
tion with other species were found (Kaplan & Štěpánek 2003). ITS sequencing also did
not detect any indication of hybridization (J. Fehrer, unpublished data). We therefore
interpret this plant as an autotriploid resulting from the combination of an unreduced (n =
26) and a normal reduced (n = 13) gamete. Production of unreduced gametes in plants has
been thoroughly studied and is considered to be the main process involved in the origin of
polyploid plants (Bretagnolle & Thompson 1995). Alternatively, the triploid plant might
have arisen from the mating of a diploid with a tetraploid. As tetraploid plants have not
been detected so far in P. pusillus, we consider the first alternative as more probable. The
observed sterility of the triploid sample probably results from difficulties involved in chro-
mosome pairing.
Potamogeton richardii Solms [syn.: P. thunbergii auct.]
2n = ca 104
2442:T
ANZANIA, Rukwa Region: small pond fed by permanent spring in Wipanga, 7 km N–NNE of
Sumbawanga, 7°52'09.4"S, 31°38'05.8"E, alt. 2144m, 21 X 2011, coll. R. v. Blittersdorff, cult. & coll. Z. Kaplan
2442.
This species is confined to Africa and Madagascar (Kaplan & Symoens 2005). The
only chromosome record published for this species is 2n = 42 for Burundi (Symoens et al.
1979). Our karyological observation was confirmed using flow cytometry and the genome
size (2C-value) of the sample was found to be almost identical to that of the octoploid (2n
= 104) sample 856 of P. illinoensis and significantly different from that of tetraploids and
hexaploids (P. Trávníček & Z. Kaplan, unpublished data).
442 Preslia 85: 421–482, 2013
Potamogeton richardsonii (A. Benn.) Rydb.
2n = 52
1056:C
ANADA, Manitoba: Snow Creek at west end of Snow Lake, town of Snow Lake, 60 mi. ENE of Cranberry
Portage, 20 VIII 1998, coll. C. B. Hellquist & C. E. Hellquist, cult. & coll. Z. Kaplan 1056 (Fig. 2g). – 1595: USA,
Massachusetts, Berkshire Co.: Berkshire Pond at Lanesborough, 42°30'28"N, 73°11'50"W, alt. 301 m, 21 VII
2005, coll. Z. Kaplan & C. B. Hellquist 05/343, cult. & coll. Z. Kaplan 1595.
Our counts for this North American species are in accordance with the previous records
for Minnesota, USA (Stern 1961, as n = 26) and Manitoba, Canada (Löve & Ritchie 1966,
Löve & Löve 1975a). There is a different count of 2n = 26 in two publications, which also
contain other dubious or demonstrably incorrect numbers: one is unspecified, for North
America (Löve 1954a, b; see also the discussion under P. zosteriformis), the other is for the
Russian Far East by Probatova & Sokolovskaya (1986).
Potamogeton robbinsii Oakes
2n = ca 52
1596: USA, Massachusetts, Berkshire Co.: Berkshire Pond at Lanesborough, 42°30'28"N, 73°11'50"W, alt. 301
m, 21 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/344, cult. & coll. Z. Kaplan 1596. – 1667: USA, Vermont,
Rutland Co.: NE corner of Lake Hortonia 2.5 km NE of Hortonia, Sudbury, 43°45'09"N, 73°12'38"W, alt. 148 m,
25 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/398, cult. & coll. Z. Kaplan 1667.
Our counts for this North American species correspond to both published records, one
for Minnesota, USA (Stern 1961, as n = 26) and the other for Manitoba, Canada (Löve &
Löve 1981).
Potamogeton rutilus Wolfg.
2n = 26
1431:P
OLAND, Województwo Lubelskie, Łęczyńsko-Włodawskie Lakeland: Rotcze Lake near Urszulin,
51°22'39"N, 23°06'46"E, 22 VIII 2002, coll. J. Zalewska-Gałosz, cult. & coll. Z. Kaplan 1431.– 2115:F
INLAND,
Uusimaa, Espoo: western edge of Matalajärvi Lake at Högnäs, 60°15'14.2"N, 24°41'03.9"E, alt. 23 m, 18 VII
2009 coll. Z. Kaplan & P. Uotila 09/323, cult. & coll. Z. Kaplan 2115.
There is a single chromosome record published for this species, which occurs in the
northern half of Europe and western Asia: Palmgren (in Tischler 1950) records 2n = 26 for
material that perhaps originated from Scandinavia. Another record claiming 2n = 52 for
this species is published for Canada by Löve & Löve (1981). However, because P. rutilus
does not occur in North America, the record must be discarded as it was presumably estab-
lished on another taxon (see also the discussion under P. zosteriformis).
Potamogeton sarmaticus Mäemets
2n = 52
1918:R
USSIA, region Voronezh (Voronezhskaya oblast’): small swampy water reservoir in nature reserve
Khopërskiy zapovednik 6 km SW of Varvarino, 24 VIII 2007, coll. E. Pechenyuk, cult. & coll. Z. Kaplan 1918.
This species was described only recently (Maemets 1979) and is closely related to
P. gramineus (Kaplan & Fehrer 2011; see also below). It is endemic to Kazakhstan, southern
Kaplan et al.: Chromosome numbers of Potamogetonaceae 443
and eastern Ukraine and small adjacent regions of southern European Russia. The chro-
mosome number presented here is the first one for this species.
Potamogeton schweinfurthii A. Benn.
2n = 104
861:K
ENYA, coll. P. Denny, cult. & coll. Z. Kaplan 861 (Fig. 2o). – 1883:PORTUGAL: prov. Algarve, distr. Faro:
local irrigation channel system 2 km SW of Rogil, 5 km N of Aljezur, 37°21'54"N, 8°48'32"W, alt. 90 m, 16
I 2007, coll. U. Schwarzer, cult. & coll. Z. Kaplan 1883. – 1951:I
TALY, Tuscany, prov. Arezzo: artificial lakes
along Tevere (Tiber) River 3.5 km N of Anghiari: the lake 0.9 km NNW of Viaio, 43°34'33.4"N, 12°03'21.0"E,
alt. 330 m, 12 VIII 2008, coll. Z. Kaplan et al. 08/608, cult. & coll. Z. Kaplan 1951.
This species has its main distribution in Africa, Madagascar, Mascarene Islands and the
Azores (Kaplan & Symoens 2005). Recently it was also discovered in southern Europe
(Kaplan 2005b) and subsequently identified to be more widespread in Mediterranean
Europe (Lastrucci et al. 2010, Aymerich et al. 2012). The chromosome counts presented
here are the first for this species. The occurrence of octoploids is exceptional in
Potamogeton. Besides P. schweinfurthii, they are recorded only in the morphologically
similar and closely related P. illinoensis, which is allopatric in North and South America,
and another African species, P. richardii.
Potamogeton spirillus Tuckerm.
2n = 28
1695: USA, New Hampshire, Carroll Co.: mouth of West Branch Brook on Ossipee Lake (NW shore) 3 km ESE
of West Ossipee, 43°48'33"N, 71°09'49"W, alt. 124 m, 29 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/418,
cult. & coll. Z. Kaplan 1695 (Fig. 1l).
This species is distributed in north-eastern USA and adjacent south-eastern Canada.
Our chromosome count is the first for this species.
Potamogeton strictifolius A. Benn.
2n = 26
1707: USA, Maine, Aroostook Co.: Nickerson Lake at south-eastern margin of New Limerick, Linneus Twp.,
5 km WSW of Houlton, 46°05'32"N, 67°54'43"W, alt. 116 m, 2 VIII 2005, coll. Z. Kaplan & C. B. Hellquist
05/434, cult. & coll. Z. Kaplan 1707.
This species occurs in north-western, central and eastern North America. Only a single
chromosome count is recorded for this species: 2n = 52 by Löve (1954a) without any
details of its origin. This count is rather surprising, because no linear-leaved species
proved to be tetraploid in this study (see the general discussion below). This count
appeared in a study that also included other doubtful records (see discussion under
P. zosteriformis). We therefore dismiss this record as untrustworthy and consider our
count as the first one that is actually for this species.
444 Preslia 85: 421–482, 2013
Potamogeton trichoides Cham. et Schlecht.
2n = 26
1903:C
ZECH REPUBLIC, distr. Karlovy Vary: Bražecké Hliňáky fishponds 0,5–0,9 km WSW of Bražec near
Bochov, 50°10'19,7"N, 13°02'17,4"E, alt. 692 m, 23 VII 2007, coll. Z. Kaplan 07/357, cult. & coll. Z. Kaplan
1903 (Fig. 1f).
This species occurs in Europe, northern, eastern and southern Africa and Asia. Our
observation is in accordance with the previous records of 2n = 26 for Sweden by Palmgren
(1939), for Slovakia by Uhríková (in Májovský et al. 1978) and for Morocco by Talavera
& García Murillo (1992, as n = 13).
Potamogeton wrightii Morong [syn.: P. malaianus auct.]
2n = 52
1239:J
APAN, Honshu, Chiba Prefecture (Chiba-ken): Tegagawa (Tega River) NE of Tokyo, 2000, coll. N. Tanaka,
cult. & coll. Z. Kaplan 1239.
This species occurs in south-eastern and eastern Asia and on Pacific islands (Wiegleb
1990b, 2002). Almost all published chromosome numbers for this species correspond to
our observation. They are recorded for the Russian Far East by Probatova et al. (2006, as
P. malaianus), for Japan by Harada (1942, as P. malaianus) and Takusagawa (1961, as
P. malaianus) and for China by Guo (in Du et al. 2009). Only recently Wan et al. (2012)
reported aneuploid variation in chromosome numbers (2n = 48, 50, 51 and 52), which has
never been reported for any broad-leaved Potamogeton. The figures presented in that
study are not of the quality to allow such precise chromosome counting.
Potamogeton zosteriformis Fernald
2n = 28
1490 & 1491:CANADA, British Columbia: Shuswap River under bridge at Cliff Avenue in Enderby, 18 km SSE of
Salmon Arm, 50°33'08"N, 119°08'00"W, alt. 366 m, 21 IX 2003, coll. F. Lomer, cult. & coll. Z. Kaplan 1490 &
1491 (Fig. 1m). – 1591: USA, Massachusetts, Berkshire Co.: pond on Kinderhook Creek at crossroads of Route
43 and Whitman Road in Hancock, 42°34'40"N, 73°17'51"W, alt. 385 m, 21 VII 2005, coll. Z. Kaplan & C. B.
Hellquist 05/339, cult. & coll. Z. Kaplan 1591. – 1612: USA, Vermont, Washington Co.: Bliss Pond 2.5 km N of
Adamant, Calais, 44°21'04"N, 72°30'05"W, alt. 369 m, 22 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/353,
cult. & coll. Z. Kaplan 1612.
This species is a North American vicariant of the Eurasian P. compressus. These
allopatric species are only weakly differentiated morphologically (Kaplan & Marhold
2012) and are genetically closely related (see below).
There is only a single chromosome count reported for this species, which appeared in
a problematic phytogeographical paper by Löve (1954a). He aligned pairs of
substitutional taxa in a table, with one species in each pair occurring in Europe and the
other confined to North America. The first couple included European P. compressus, with
2n = 26, and American P. zosteriformis, for which 2n = 52 is indicated. The second pair
consisted of European P. rutilus, with 2n = 26, and American P. strictifolius, for which 2n
= 52 is claimed. No details on chromosome counting and the origin of the samples are
provided in this phytogeographical paper. Two tetraploid counts 2n = 52 recorded for
Kaplan et al.: Chromosome numbers of Potamogetonaceae 445
linear-leaved species, a group that was found here to consist exclusively of diploids (see
the discussion on the pattern of chromosome number variation below), is rather surprising.
In spite of the clear-cut differentiation claimed in the first paper, in a later publication Löve
& Löve (1981) report both P. compressus and P. rutilus (i. e. the European members of the
species pairs) as diploids for Manitoba, Canada (i. e. in the area where these European spe-
cies should be, according to the Löve’s own observations, substituted by the North Ameri-
can tetraploids). The table in Löve (1954a) includes also two other doubtful records: dip-
loid counts for P. perfoliatus (as P. bupleuroides) and P. richardsonii, which both proved
to be tetraploids in this study. This was changed again in the later study that cites
P. richardsonii as tetraploid. The herbarium vouchers listed by Löve & Löve (1981) are all
dated between 1951 and 1953 (specimens seen in DAO and S, see also below), that is,
prior to the publication of the 1954 paper. This indicates that the chromosome records
given in both papers were apparently based on the same plants but may have been con-
fused during the preparation of the manuscripts.
When attempting to disentangle this confusing story, the possibility of incorrect identi-
fication of samples was also taken into account. We intended to examine voucher speci-
mens but, unfortunately, no details on the origin of the plants or the herbarium where the
respective vouchers were preserved are given by Löve (1954a). In the later paper, Löve &
Löve (1981) indicate the vouchers are “in COLO or WIN”. However, none of the
Potamogeton vouchers (and of many other plants) were actually presented to COLO (Tim
Hogan, personal communication) or WIN (Bruce A. Ford, personal communication). We
attempted to trace the collections also in other institutions where the Löves are known to
have worked. No Potamogeton vouchers of Löves are located at MT (Stuart G. Hay, per-
sonal communication). We also found no North American material collected by Löves at
LD in spite of searching through all of the collections. Eventually, five vouchers for chro-
mosome counts published by Löve & Löve (1981) were discovered by Gisèle Mitrow at
DAO. We examined these specimens and found that only three of these vouchers (for
P. berchtoldii,P. gramineus and P. richardsonii) were correctly identified. However, the
voucher Löve & Löve 5260, on which the chromosome count for S. pectinata is based
(Löve & Löve 1981, as P. pectinatus) actually belongs to S. vaginata. Another collection,
Löve & Löve 5590, which is a voucher for the chromosome record for S. vaginata (Löve &
Löve 1981, as P. vaginatus), consists of two herbarium sheets, one of which is S. vaginata
but the other is S. pectinata. It is thus unclear which of these two species was actually used
for the chromosome counts and this particular record must therefore be considered doubt-
ful. A voucher for a count made on P. berchtoldii was unexpectedly found at S. The vouch-
ers for the dubious records described above are considered as missing, as they have not
been located in any of the herbaria consulted.
This peculiarly unfortunate combination of problematic circumstances prompted us to
consider all six dubious records discussed above (i. e., the diploid counts 2n = 26 for
P. perfoliatus and P. richardsonii and the tetraploid counts 2n = 52 for P. zosteriformis and
P. strictifolius from Löve 1954a, and the records from Löve & Löve 1981 on the diploid
counts of 2n = 26 for P. compressus and P. rutilus from North America where these species
do not occur) as unreliable and to exclude them from further consideration.
As a consequence, we consider our four records of 2n = 28 for P. zosterifomis as the
first counts actually established on this species. The same number was also found in
its vicariant species P. compressus. The validity of the newly established chromosome
446 Preslia 85: 421–482, 2013
number gains further indirect support from counts of 2n = 27 determined for hybrids
involving P. zosterifomis and several linear-leaved species with 2n = 26 (see below).
Potamogeton ×absconditus Z. Kaplan, Fehrer et Hellq. [= P. perfoliatus ×P. richardsonii]
2n = 78
1720: USA, Maine, Aroostook Co.: oxbow of Pettingrill Brook 1.5 km above its mouth to Aroostook River, just
S of Route 164, Washburn, 6 km NNW of Presque Isle, 46°44'20"N, 68°01'59"W, alt. 130 m, 2 VIII 2005, coll.
Z. Kaplan & C. B. Hellquist 05/444, cult. & coll. Z. Kaplan 1720.
The existence of this hybrid was only recently documented by molecular analysis
(Kaplan et al. 2009). It is known to occur in Maine and Vermont and is likely to be more
widespread in the north-eastern USA where both species co-occur (Kaplan & Reveal
2013). The sample used here for chromosome counting showed a stronger signal of the
ITS variant from P. richardsonii than that from P. perfoliatus. This is interpreted as a pos-
sible later generation backcross to P. richardsonii (Kaplan et al. 2009).
The chromosome number identified here provides additional information for determin-
ing the origin of this hybrid plant. As both parental species are tetraploid and this hybrid is
hexaploid, it apparently resulted from the combination of an unreduced gamete (n = 52)
and a normal reduced gamete with 26 chromosomes. Hybrids are more likely to produce
unreduced gametes than pure species because of potentially disturbed meiosis. We there-
fore assume that an unreduced egg cell of P. perfoliatus ×P. richardsonii was fertilized by
pollen from P. richardsonii. Other P. perfoliatus ×P. richardsonii hybrids may not neces-
sarily be hexaploid but tetraploid like the parental species.
Potamogeton ×angustifolius J. Presl [= P. gramineus ×P. lucens]
2n = 52
333:C
ZECH REPUBLIC, distr. Česká Lípa: Držník fishpondin forest 1.1 km ESE of Hradčany, 4 km S of Mimoň,
50°36'37"N, 14°43'23"E, alt. 273 m, 18 IX 1996, coll. Z. Kaplan 96/640, cult. & coll. Z. Kaplan 333.
This is a relatively well-known hybrid that is recorded for many countries in Europe
and a few regions of Asia. The chromosome number determined in this study isconsistent
with the theoretical assumption based on the chromosome numbers of the parental species
(2n = 52 repeatedly recorded for each of them). This is the firstchromosome count for this
hybrid.
Potamogeton ×assidens Z. Kaplan, Zalewska-Gałosz et M. Ronikier [= P. nodosus ×
P. perfoliatus]
2n = 52
1944:M
ONTENEGRO, distr. Bar: shallow edge of Skadarsko jezero (Lake Scutari, Lake Skadar) at abandoned port
of Pristan, 1.1 km N–NNE of Seoca, 5 km ESE of Virpazar, 42°13'47.7"N, 19°08'50.6"E, alt. 6 m, 13 VII 2008,
coll. Z. Kaplan 08/573, cult. & coll. Z. Kaplan 1944. – 1948:L
ITHUANIA, Verknë River under bridge 1 km S of
Lielionys, 54°33'26.0"N, 24°20'36.8"E, 24 VII 2008, coll. W. Gałosz & J. Zalewska-Gałosz, cult. & coll.
Z. Kaplan 1948.
This hybrid was discovered and described only recently, based on fresh material from
Poland and herbarium collections from Africa (Zalewska-Gałosz et al. 2010). It is here for
Kaplan et al.: Chromosome numbers of Potamogetonaceae 447
the first time recorded for Montenegro and Lithuania. The chromosome number of this
hybrid is identified here for the first time and is identical to that of its parental species.
Potamogeton ×billupsii Fryer [= P. coloratus ×P. gramineus]
2n = ca 40
2055:U
NITED KINGDOM, Wales, Isle of Anglesey: Talwrn, shallow pools in Cors Bodeilio National Nature
Reserve, 53°16'16.4"N, 04°14'52.1"W, alt. 34 m, VI 2002, coll. R. V. Lansdown, cult. & coll. Z. Kaplan 2055.
This is an extremely rare hybrid known from only a few sites in the British Isles. The
chromosome count was identified here for the first time and it is consistent with the num-
ber expected for a hybrid between the parental species (2n = 28 in P. coloratus, 2n = 52 in
P. gramineus).
Potamogeton ×cognatus Asch. et Graebn. [= P. perfoliatus ×P. praelongus]
2n = 52
1226:D
ENMARK, Jylland (Jutland), region Midtjylland (Central Denmark Region): GudenåRiver near Randers,
17 VIII 2000, coll. C. D. Preston, cult. & coll. Z. Kaplan 1226.
This hybrid is known from only a few countries in the northern half of Europe. The
identity of the sample studied was recently confirmed using DNA analysis (Kaplan &
Fehrer 2013). The chromosome count presented here is the first for this hybrid and is the
same as for its parental species.
Potamogeton ×cooperi (Fryer) Fryer [= P. crispus ×P. perfoliatus]
2n = 52
1248:U
NITED KINGDOM, Wales, Pembrokeshire Co.: River Solva, 8 VI 2001, coll. T. D. Dines & C. D. Preston,
cult. & coll. Z. Kaplan 1248. – 1420:C
ZECH REPUBLIC, distr. Břeclav: small water reservoir “Malá laguna” 1.4 km
ESE of Pasohlávky village, 48°53'45"N,16°34'01"E, alt. 170 m, 21 VI 2002, coll. J. Rydlo, cult. & coll. Z. Kaplan
1420.
This hybrid is known from several countries mainly in the northern half of Europe.
Both samples used for determining the chromosome number were previously analysed
genetically to confirm their origin (Kaplan & Fehrer 2004). Our chromosome counts are
the first established for this hybrid and are identical to those of the parental species.
Potamogeton ×drepanoides Z. Kaplan [= P. berchtoldii ×P. oxyphyllus]
2n = 26
1236:J
APAN, Honshu, Hiroshima Prefecture (Hiroshima-ken): fishpond 1 km ENE of University campus SW of
city centre of Higashi-Hiroshima, 34°24'23"N, 132°43'47"E, alt. 227 m, 4 X 2000, coll. L. Adamec, cult. & coll.
Z. Kaplan 1236. – 1238:J
APAN, Honshu, Hiroshima Prefecture (Hiroshima-ken): water reservoir in Yamanaka
park at University campus SW of city centre of Higashi-Hiroshima, 34°24'12"N, 132°43'09"E, alt. 234 m, 4 X
2000, coll. L. Adamec, cult. & coll. Z. Kaplan 1238.
This hybrid is known only from two close localities. It has the same chromosome num-
ber as its parental species. It is described in terms of its morphology on p. 467.
448 Preslia 85: 421–482, 2013
Potamogeton ×faxonii Morong [= P. illinoensis ×P. nodosus]
2n = 78
1654: USA, Vermont, Addison Co.: fast flowing section of Otter Creek just at confluence with New Haven River
1 km W of Brooksville, Weybridge, 44°03'45"N, 73°10'39"W, alt. 67 m, 25 VII 2005, coll. Z. Kaplan & C. B.
Hellquist 05/387, cult. & coll. Z. Kaplan 1654.
The exact distribution of this hybrid is poorly known because the variation in its mor-
phology overlaps that of its parental species. It may be widespread in North and Central
America. The chromosome count presented here is the first recorded for this hybrid. It is
intermediate between the chromosome numbers of its parental species (2n = 52 in
P. nodosus, 2n = 104 in P. illinoensis).
Potamogeton ×gessnacensis G. Fisch. [= P. natans ×P. polygonifolius]
2n = 40
1286:U
NITED KINGDOM, Wales, Powys Co.: small pool at Afon Marteg (river) at Gilfach, ca 3.5 km N of
Rhayader, alt. 240 m, 16 VII 2001, coll. A. O. Chater & C. D. Preston, cult. & coll. Z. Kaplan 1286 (Fig. 1o).
This is an extremely rare hybrid reliably documented for only two countries in Europe.
So far, only a single chromosome count has been published for this hybrid: 2n = ca 39 by
Preston et al. (1998). Although inexact, it was sufficient to show that their plant was
a hybrid between a diploid and a tetraploid. Our chromosome count exactly corresponds to
the number that may be expected for a hybrid between species with 2n = 28
(P. polygonifolius) and 2n = 52 (P. natans).
Potamogeton ×hagstroemii A. Benn. [= P. gramineus ×P. richardsonii]
2n = ca 52
1647: USA, Vermont, Addison Co.: fast flowing section of Otter Creek just at confluence with New Haven River
1 km W of Brooksville, Weybridge, 44°03'45"N, 73°10'39"W, alt. 67 m, 25 VII 2005, coll. Z. Kaplan & C. B.
Hellquist 05/380, cult. & coll. Z. Kaplan 1647.
This hybrid occurs in North America but its exact distribution is poorly known. It has
the same chromosome number as its parental species. This is the first chromosome record
for this hybrid.
Potamogeton ×haynesii Hellq. et G. E. Crow [= P. strictifolius ×P. zosteriformis]
2n = 27
1673:C
ANADA, Saskatchewan: Egg Lake S of Cumberland House, coll. C. B. Hellquist, cult. & coll. Z. Kaplan
1673.
This hybrid is known from about 30 localities in the north-eastern United States and
adjacent south-eastern Canada (Hellquist & Crow 1986). The chromosome count pre-
sented here is the first for this hybrid. It is intermediate between the chromosome numbers
of its parental species (2n = 26 in P. strictifolius, 2n = 28 in P. zosteriformis).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 449
Potamogeton ×lanceolatifolius (Tiselius) C. D. Preston [= P. gramineus ×P. nodosus]
2n = 52
1005:S
WEDEN, prov. Småland, Kalmar: Alsterån River 0.8 km NNW(–N) of bridge in Strömsrum, 3 km SE of
Ålem, 56°56'36"N, 16°24'52"E, alt. 6 m, coll. Z. Kaplan 98/342, cult. & coll. Z. Kaplan 1005.
This taxon was first described as one of several forms of P. gramineus by Tiselius
(1894–1897, see also Kaplan 2010c). Based on a careful morphological investigation of the
type collection, Hagström (1916) correctly noted that these plants have sterile pollen, sug-
gested their hybrid origin and interpreted them as a hybrid P. gramineus ×P. polygonifolius.
This taxonomic view was adopted by later researchers and held for almost a century. How-
ever, a recent molecular investigation of plants from the original clones still growing at the
type locality demonstrated that one of the parental species was not P. polygonifolius as
previousy believed, but the morphologically and anatomically similar species P. nodosus
(Kaplan & Fehrer 2011). The chromosome count presented here, the first one established for
this hybrid combination, is identical to that of its parental species, whereas P. polygonifolius,
one of the previously believed parental species, differs in being diploid with 2n = 28.
Potamogeton ×lintonii Fryer [= P. crispus ×P. friesii]
2n = 65
2119:G
ERMANY, Nordrhein-Westfalen (North Rhine-Westphalia), Lower Rhine Basin (Niederhein): ditch
between fields (550 m upstream of its mouth to Kleine Niers River) at bridge on road Kempen – Straelen, 2.7 km
W of Kerken, 51°27'11.6"N, 06°19'32.8"E, alt. 25 m, coll. Z. Kaplan, K. van de Weyer & J. Bruinsma 09/326,
cult. & coll. Z. Kaplan 2119 (Fig. 2j).
This is an extremely rare hybrid currently known only from the British Isles (Dandy
1975, Preston 1995) and the Netherlands (Ploeg 1990, Meijer & Ploeg 1994) and tenta-
tively recorded for Germany (Wiegleb et al. 2008). The records for Belgium (Vannerom &
Andriessen 1987) are erroneous, based on underdeveloped plants of P. crispus with plane
leaves (Z. Kaplan, unpublished data). Potamogeton ×lintonii is a hybrid between highly
unrelated species, diploid P. friesii (2n = 26) and tetraploid P. crispus (2n = 52). This may
be the reason why the parental species rarely hybridize. The chromosome count presented
here is the first for this hybrid. The recorded pentaploid chromosome number is best
explained as a result of fusion of an unreduced gamete of P. crispus (n = 52) and a normal
reduced gamete of P. friesii (n = 13).
Potamogeton ×luxurians Z. Kaplan [= P. amplifolius ×P. illinoensis]
2n = 78
1625: USA, Vermont, Orleans Co.: Lake Parker 1 km WSW of West Glover, 44°43'34"N, 72°13'53"W, alt. 396 m,
22 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/362, cult. & coll. Z. Kaplan 1625.
This is a little-known North American hybrid sometimes incorrectly annotated as
P. ×scoliophyllus (Hagström 1916, Scoggan 1978, Brayshaw 2000). Its nomenclature is
analysed on p. 469–471. The chromosome count presented here is the first recorded for
this hybrid. It is intermediate between the chromosome numbers of its parental species
(2n = 52 in P. amplifolius, 2n = 104 in P. illinoensis).
450 Preslia 85: 421–482, 2013
Potamogeton ×malainoides Miki [= P. distinctus ×P. wrightii]
2n = ca 52
1763:J
APAN, Kyushu, Fukuoka Prefecture (Fukuoka-ken), Kitakyusyu: Kokura-Minami, Jingu-ji, 16 V 1999,
coll. N. Tanaka, cult. & coll. Z. Kaplan 1763.
This hybrid is known from several regions of south-eastern and eastern Asia where the
parental species co-occur. The chromosome number of our sample is in agreement with
previous records for this hybrid (Harada 1942, Takusagawa 1961) and corresponds to the
count of 2n = 52 for both parental species.
Potamogeton ×nitens Weber [= P. gramineus ×P. perfoliatus]
2n = 52
879:G
ERMANY, Mecklenburg-Vorpommern, Güstrow: Lake Gültz (Gültzsee) 2.2 km SSW of Dobbin,
53°35'23"N, 12°19'04"E, 15 VIII 1997, coll. Z. Kaplan 97/828, cult. & coll. Z. Kaplan 879 (Fig. 2h). – 999:
SWEDEN, prov. Skåne: Björkaån River 0.5 km ENE of church in Björka, 4 km WNW of Sjöbo, 55°39'28"N,
13°38'35"E, alt. 24 m 12 VIII 1998, coll. Z. Kaplan 98/335, cult. & coll. Z. Kaplan 999. – 1824:S
WEDEN, prov.
Skåne, municipality (kommun) of Kristianstad: shallow bay at E bank of SE part of Hammarsjön Lake1.7 km SW
of Rinkaby, 55°57'59"N, 14°14'45"E, sea level, 11 VIII 2006, coll. Z. Kaplan, S. Skällberg, J. Svensson & A.
Jacobson 06/359, cult. & coll. Z. Kaplan 1824. – 2148:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), distr.
Ziminskiy: stream (side arm of Oka River) below road in village Osipovskiy, 8.5 km WSW of Maslyanogorsk,
53°31'13.7"N, 101°33'10.6"E, alt. 517 m, 21 VIII 2009, coll. Z. Kaplan & V. Chepinoga 09/373, cult. & coll.
Z. Kaplan 2148.
This hybrid is widespread but only locally common in boreal and temperate regions of
the Northern Hemisphere. Molecular confirmation of the identities of samples 879 and
999 was published previously (Kaplan & Fehrer 2006). The chromosome counts pre-
sented here are all identical with those of its parental species. Until now, only a single
approximate chromosome number 2n = ca 52 was published for the British Isles by
Hollingsworth et al. (1998).
Potamogeton ×ogdenii Hellq. et R. L. Hilton [= P. hillii ×P. zosteriformis]
2n = 27
1590: USA, Massachusetts, Berkshire Co.: pond on Kinderhook Creek at crossroads of Route 43 and Whitman
Road in Hancock, 42°34'40"N, 73°17'51"W, alt. 385 m, 21 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/338,
cult. & coll. Z. Kaplan 1590.
This hybrid is known to occur at about 20 localities in the north-eastern United States and
one site in adjacent south-eastern Canada (Hellquist & Hilton 1983, Haynes & Hellquist
2000, Hellquist & Mertinooke-Jongkind 2002). This taxon is not a species of hybrid origin
as suggested by the original authors and recognized by the recent American literature but
a recent hybrid involving P. hillii and P. zosteriformis as the ITS copies of both parental
species are clearly recognizable and not yet homogenized by concerted evolution as in pure
species of Potamogeton (J. Fehrer & Z. Kaplan, unpublished data). The chromosome count
presented here is the first for this hybrid. It is intermediate between the chromosome num-
bers of its parental species (2n = 26 in P. hillii,2n=28inP. zosteriformis).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 451
Potamogeton ×rivularis Gillot [= P. berchtoldii ×P. polygonifolius]
2n = 27
2056:F
RANCE, Burgundy, Dept. Nièvre: granitic mountainous massif Le Morvan, La Cure River (rivière la Cure)
at site called “le Furtiau” 1.3 km NE of Montsauche-les-Settons, 0.8 SSW of Nataloup, 47°13'34"N, 04°02'20"E,
alt. 517 m, 2 IX 2003, coll. R. V. Lansdown & O. Bardet, cult. & coll. Z. Kaplan 2056.
This is an extremely rare hybrid so far recorded only for France. The sample investi-
gated originates from the type locality. Its chromosome count corresponds to the number
expected for a hybrid between species with 2n = 26 (P. berchtoldii) and 2n = 28
(P. polygonifolius). This is the first chromosome record for this hybrid.
Potamogeton ×salicifolius Wolfg. [= P. lucens ×P. perfoliatus]
2n = 52
972:I
TALY, Lombardy, prov. Como: eastern shore of northern edge of Lago di Como (lake) 0.8 km SSE of Gera
Lario, 3.3 km ENE of Domaso, 46°09'46"N, 09°22'48"E, alt. 200 m, 18 VI 1998, coll. Z. Kaplan, cult. & coll.
Z. Kaplan 972. – 1958:S
WEDEN, prov. Uppland, Stockholm county, municipality (kommun) of Stockholm, Stock-
holm parish: channel Riddarholmskanalen in Gamla Stan (Old Town) in center of Stockholm City, 59°19'28.2"N,
18°03'59.3"E, sea level, 28 VIII 2008, coll. Z. Kaplan & A. Svenson 08/629, cult. & coll. Z. Kaplan 1958.
2n = ca 52
2137:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), border of Alarskiy & Cheremkhovskiy distr.: Golumet’
River at bridge 2.2 km SW of village Nygda, 11 km SE of Alar’, 52°59'36.4"N, 102°40'01.3"E, alt. 445 m, 19 VIII
2009, coll. Z. Kaplan & V. Chepinoga 09/363, cult. & coll. Z. Kaplan 2137.
2n = 78
1017:S
WEDEN, prov. Uppland: river connecting lakes Skarren and Oxundasjön 300 m SE of Rosendal settlement,
2 km ENE of Runsa, 5 km NW of Upplands Väsby, 59°33'48"N, 17°51'06"E, alt. 5 m, 15 VIII 1998, coll.
Z. Kaplan 98/361, cult. & coll. Z. Kaplan 1017 (Fig. 2k).
This hybrid is recorded for several European countries and Siberia. The majority of our
records correspond to the only published record that comes from the British Isles
(Hollingsworth et al. 1998, as 2n = ca 52) as well as the chromosome counts of both paren-
tal species. The exception is sample 1017, which is hexaploid. It apparently resulted from
a fusion of reduced and unreduced gametes.
Potamogeton ×schreberi G. Fisch. [= P. natans ×P. nodosus]
2n = 52
1276:F
RANCE, Lorraine, Moselle: Blies River upstream of Bliesbruck, ca 49°08'10"N,07°11'03"E, alt. 205 m, 14
VII 2001, coll. P. Wolff, cult. & coll. Z. Kaplan 1276. – 1278:G
ERMANY, Saarland: Blies River above bridge at
south-eastern edge of Reinheim, ca 49°08'15"N, 07°11'20"E, alt. 207 m, 14 VII 2001, coll. P. Wolff, cult. & coll.
Z. Kaplan 1278. – 1279:G
ERMANY, Saarland: Blies River below bridge at south-eastern edge of Reinheim,
ca 49°08'08"N, 07°10'57"E, alt. 207 m, 14 VII 2001, coll. P. Wolff, cult. & coll. Z. Kaplan 1279. – 1889:C
ZECH
REPUBLIC, distr. České Budějovice: Stropnice stream 0.9 km ENE of Třebeč, 48°52'39.3"N, 14°41'31.5"E, alt.
450 m, 29 VI 2007, coll. Z. Kaplan 07/214, cult. & coll. Z. Kaplan 1889.
This hybrid is known from only a small number of European countries. Identities of all
the samples studied were confirmed using molecular methods (Kaplan & Wolff 2004,
Kaplan & Fehrer 2009). Our chromosome counts are the first for this hybrid. They are
identical to those of the parental species.
452 Preslia 85: 421–482, 2013
Potamogeton ×serrulifer Z. Kaplan [= P. crispus ×P. schweinfurthii]
2n = 78
1953:I
TALY, Tuscany, prov. Siena: water reservoir 1.1 km ENE of San Fabiano farm, 1.6 km NE of Monteroni
d’Arbia, 43°14'33.7"N, 11°26'11.3"E, alt. 180 m, 12 VIII 2008, coll. Z. Kaplan, L. Lastrucci, F. Frignani & B.
Foggi 08/612, cult. & coll. Z. Kaplan 1953.
This hybrid is currently only known from a single site in a relatively small area of the
overlap of the distributional ranges of its parental species. Its chromosome number is
intermediate between those of its parental species (2n = 52 in P. crispus, 2n = 104 in
P. schweinfurthii). It is described morphologically on p. 471.
Potamogeton ×spathuliformis (J. W. Robbins) Morong [= P. gramineus ×P. illinoensis]
2n = 78
1663: USA, Vermont, Rutland Co.: Burr Pond 2.5 km SSE of Hyde Manor, Sudbury, 43°46'06"N, 73°10'57"W,
alt. 157 m, 25 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1663.
This hybrid is known from scattered locations mainly in eastern USA. The chromosome
count presented here is the first for this hybrid. It is intermediate between the chromosome
numbers of its parental species (2n = 52 in P. gramineus, 2n = 104 in P. illinoensis).
Potamogeton ×torssanderi (Tiselius) Dörfler [= P. gramineus ×P. lucens ×P. perfoliatus]
2n = 78
1006:S
WEDEN, prov. Södermanland: north-eastern edge of Sillen Lake near Vårdinge, 59°01'19"N, 17°21'29"E,
alt. 11 m, 13 VIII 1998, coll. Z. Kaplan 98/343, cult. & coll. Z. Kaplan 1006 (Fig. 2l).
This is the only unequivocally documented triple hybrid in this family. It is known only
from its type locality. After more than a century of taxonomic uncertainty about this taxon,
Kaplan & Fehrer (2007) used DNA sequencing of plant material from the original popula-
tion and identified it as a triple hybrid between P. gramineus,P. lucens and P. perfoliatus.
Plants from the same clone were used also for chromosome counting. This triple hybrid
has apparently arisen from combination of an unreduced gamete (n = 52) of a primary
binary hybrid and a normal reduced gamete (n = 26) of a third species.
Potamogeton ×undulatus Wolfg. [= P. crispus ×P. praelongus]
2n = 52
1024 & 1025:D
ENMARK, Jylland (Jutland), Region Syddanmark (Region of Southern Denmark): RibeåRiver at
western edge of Varming, 4 km ESE of Ribe, 55°19'07"N, 08°50'52", alt. 1 m, 19 VIII 1998, coll. Z. Kaplan
98/374, cult. & coll. Z. Kaplan 1024 & 1025 (Fig. 2i).
This hybrid is known from several countries mainly in the northern half of Europe and
from a single location in the USA. The identity of the samples studied was recently con-
firmed using DNA analysis (Kaplan & Fehrer 2013). The identified chromosome number
is the first for this hybrid and it is the same as that of its parental species.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 453
Potamogeton ×variifolius Thore [= P. berchtoldii ×P. natans]
2n = 39
1589:F
RANCE, Vosges du Nord, Bas-Rhin: downstream from Philippsbourg, fast flowing cool stream of
Falkensteinerbach near Breitenwasen, 2000, coll. Š. Husák & G. Thiébaut, cult. & coll. Z. Kaplan 1589.
This remarkable hybrid between a narrow-leaved and broad-leaved species is known
from Ireland, France and Germany. Its chromosome number, identified for the first time
for this hybrid, is intermediate between that of its parental species (2n = 26 in
P. berchtoldii, 2n = 52 in P. natans).
Potamogeton ×vepsicus A. A. Bobrov et Chemeris [= P. natans ×P. praelongus]
2n = 52
1739:R
USSIA, prov. Vologda, distr. Babaevo: Nozhema River at Pyazhelka, ca 60°09'N, 35°44'E, alt. 190 m,
8 VIII 2005, coll. A. Bobrov & E. Chemeris, cult. & coll. Z. Kaplan 1739.
This hybrid was only recently described from Russia and believed to be P. alpinus ×
P. natans (Bobrov & Chemeris 2006). However, subsequent molecular investigation of
shoots from the type clone showed that the taxon had been misunderstood and its correct
identity is P. natans ×P. praelongus (Kaplan & Fehrer 2011). The same plant was also
used for the first karyological analysis of this hybrid. The chromosome number is the same
as that of its parental species.
Potamogeton berchtoldii ×P. zosteriformis
2n = 27
1598 & 1600 & 1604: USA, Massachusetts, Berkshire Co.: Berkshire Pond at Lanesborough, 42°30'28"N,
73°11'50"W, alt. 301 m, 21 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/346, cult. & coll. Z. Kaplan 1598 &
1600 & 1604. – 1618: USA, Vermont, Washington Co.: Curtis Pond 0.5 km NW of Maple Corner, Calais,
44°22'36"N, 72°30'03"W, alt. 371 m, 22 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan
1618. – 1674: USA, New England, exact locality unknown, cultivated by C. B. Hellquist in Adams, Massachu-
setts, USA, cult. & coll. Z. Kaplan 1674.
This is one of several similar North American hybrids among linear-leaved species,
which was identified only recently. Its chromosome number is intermediate between those
of its parental species (2n = 26 in P. berchtoldii, 2n = 28 in P. zosteriformis).
Potamogeton distinctus ×P. natans
2n = 78
2179:I
NDIA, Kashmir, Bandipora district: outlet of Manasbal Lake at Naninara, 34°14'47"N, 74°39'18"E, alt.
1582 m, IX 2009, coll. A. H. Ganie, cult. & coll. Z. Kaplan 2179.
This is a very recently detected hybrid. The chromosome number indicates that the
investigated plant apparently resulted from the fusion of a reduced and unreduced gamete
of its parental species, which are both tetraploid with 2n = 52.
454 Preslia 85: 421–482, 2013
Potamogeton friesii ×P. pusillus
2n = 26
1669: USA, Vermont, Rutland Co.: NE corner of Lake Hortonia 2.5 km NE of Hortonia, Sudbury, 43°45'09"N,
73°12'38"W, alt. 148 m, 25 VII 2005, coll. Z. Kaplan & C. B. Hellquist, cult. & coll. Z. Kaplan 1669.
This is a little-known hybrid that is difficult to distinguish from its parental species. It
has the same chromosome number as its parental species.
Stuckenia filiformis (Pers.) Börner
2n = 78
975:S
WITZERLAND, canton Sankt Gallen: canal with fast-running water (Rheintaler Binnenkanal) 0.8 km NW of
Kriessern near Altstätten, 47°22'27"N, 09°36'12"E, alt. 407 m, 22 VI 1998, coll. Z. Kaplan 98/105, cult. & coll.
Z. Kaplan 975. – 1187:S
WITZERLAND, canton Sankt Gallen: southern edge of Bodensee (Lake Constance) 0.8 km
N–NNE of Altenrhein near Rorschach, 47°30'03"N, 09°33'18"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan, cult. &
coll. Z. Kaplan 1187 (Fig. 2m). – 1703: USA, Maine, Aroostook Co.: Nickerson Lake at south-eastern edge of
New Limerick, Linneus Twp., 5 km WSW of Houlton, 46°05'32"N, 67°54'43"W, alt. 116 m, 2 VIII 2005, coll.
Z. Kaplan & C. B. Hellquist 05/426, cult. & coll. Z. Kaplan 1703. – 2134:R
USSIA, Siberia, prov. Irkutsk
(Irkutskaya oblast’), distr. Cheremkhovskiy: Verkhnaya Iret’ River at south-western edge of Russkaya Alar’,
1 km upstream of its mouth into Bol’shaya Belaya River, 7.5 km SW of Parfenovo, 52°56'51.4"N, 102°45'29.8"E,
alt. 438 m, 19 VIII 2009, coll. Z. Kaplan & V. Chepinoga 09/360, cult. & coll. Z. Kaplan 2134. – 2543:
SWITZERLAND, canton Sankt Gallen: canal with fast-running water (Rheintaler Binnenkanal) 0.8 km NW of
Kriessern near Altstätten, 47°22'27"N, 09°36'12"E, alt. 407 m, 12 VII 2012, coll. Z. Kaplan 12/195, cult. & coll.
Z. Kaplan 2543.
This species is widely distributed in Europe, western, central and northern Asia, North
America and South America. Our records of its chromosome number are the same as the
prevailing count for this species (all as Potamogeton filiformis), as reported for Scandina-
via (Palmgren in Löve & Löve 1942, as 2n = ca 78), Iceland (Löve & Löve 1956), Russian
Far East (Yurtsev & Zhukova 1978), Canada (Löve & Ritchie 1966, Löve & Löve 1981)
and Greenland (Jörgensen et al. 1958). The only deviant count, 2n = ca 66, came from an
early report by Palmgren (1939). However, this appears to be erroneous. The author him-
self indicated it as inexact and did not include it in the chromosome catalogue of Scandina-
vian plants (Palmgren in Löve & Löve 1942), but replaced it with the count “2n = ca 78”.
Stuckenia pectinata (L.) Börner
2n = 78
841:C
ZECH REPUBLIC, distr. Hodonín: Velička navigation canal at northern edge of Strážnice, 48°54'38.5"N,
17°18'42.5"E, alt. 170 m, 25 VI 1997, coll. Z. Kaplan 97/509, cult. & coll. Z. Kaplan 841. – 1841:R
USSIA, Siberia,
prov.Irkutsk (Irkutskaya oblast’), Ust-Ordyn-Buryat autonomous okrug, distr. Alarskiy: Kuda River near Kapsal,
52°41'N, 104°40'E, 2 IX 2006, coll. V. Chepinoga, cult. & coll. Z. Kaplan 1841. – 2026:I
NDIA, Kashmir,
Bandipora district: outlet of Manasbal Lake at Naninara, 34°14'47"N, 74°39'18"E, alt. 1582 m, 27 VI 2008, coll.
A. H. Ganie, cult. & coll. Z. Kaplan 2026. – 2238:S
WITZERLAND, canton Thurgau: Untersee (Lower Lake Con-
stance), at outflow of Seerhein into Ermatinger Becken, NE of Triboltingen,47°40'00"N, 9°07'20"E, alt. 395 m, 7
IV 2010, coll. D. Richter, cult. & coll. Z. Kaplan 2238.
2n = ca 78
981:S
WITZERLAND, canton Sankt Gallen: ditch with running water 200 m SSW of Altenrhein near Rorschach,
47°29'08.3"N, 09°32'56.4"E, alt. 396 m, 23 VI 1998, coll. Z. Kaplan 98/127, cult. & coll. Z. Kaplan 981. – 1650:
USA, Vermont, Addison Co.: fast flowing section of Otter Creek just at confluence with New Haven River 1 km
Kaplan et al.: Chromosome numbers of Potamogetonaceae 455
W of Brooksville, Weybridge,44°03'45"N, 73°10'39"W, alt. 67 m, 25 VII 2005, coll. Z. Kaplan & C. B. Hellquist
05/383, cult. & coll. Z. Kaplan 1650. – 1837:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), distr. Alarskiy:
Golumet’ River near Nygda, ca 52°59'N, 102°40'E, 29 VIII 2006, coll. V. Chepinoga, cult. & coll. Z. Kaplan
1837.
There are several published records of the chromosome number of this cosmopolitan
species (all as Potamogeton pectinatus). The most frequent count is 2n = 78. This is
recorded for Germany (Scheerer 1939, as 2n = ca 78), Scandinavia (Palmgren in Löve &
Löve 1942), Finland (Arohonka 1982), British Isles (Hollingsworth et al. 1998, as 2n =
ca 78), Slovakia (Uhríková & Feráková 1978), Russia (Chepinoga et al. 2012, as 2n =
ca 78), India (Bhat et al. 1975, as n = 39), Japan (Harada 1942, as 2n = ca 78, Takusagawa
1961) and Canada (Löve & Löve 1981).
Other records are more or less controversial. Kalkman & Van Wijk (1984) report exten-
sive aneuploidy in this species around 2n = 78 and the occurrence of 17 cytotypes (2n = 70,
71, and all ranging between 73 and 87). They record high variation in chromosome num-
ber both within and between populations. For some populations as many as 10 different
cytotypes are reported. It is not clear from their paper how many plants were studied from
each population (i. e., what was the probability of recording such high variation) and thus
if the variation was between individuals or between different cells within a single or a few
individuals. An extensive variation in chromosome number, ranging from 70 to 87, is
reported also by Ceccarelli et al. (2008). Variable counts are recorded even for metaphases
in one and the same root. The most common chromosome number is 78, which they con-
sider to be the euploid chromosome number of this species. Two other records indicate
counts within this variation: Uchiyama (1989) reports 2n = 84 for Japan and Yurtsev et al.
(1975, as “P. cf. pectinatus”) record 2n = 86 for the Russian Far East. Given the obvious
technical difficulties of exactly counting the small chromosomes at the hexaploid level in
Potamogetonaceae, this variation probably does not reflect genuine variation in chromo-
some number but is rather due to counting errors.
Lower numbers of chromosomes are reported only exceptionally. Probatova &
Sokolovskaya (1986) publish for the Russian Far East an approximate count of 2n = ca 66
and Misra (1972) report an even less credible count of 2n = 42 for India. Considering the
fact that no cytotype below the hexaploid level is confirmed for the entire genus, which
represents a monophyletic group well separated from other genera (see below), we con-
sider these records as erroneous.
We examined the voucher specimen (Löve & Löve 5260, DAO) for the chromosome
count of 2n = 78 for “Potamogeton pectinatus” given by Löve & Löve (1981) and found
that it is actually Stuckenia vaginata. This chromosome record must therefore be trans-
ferred to the latter species.
Stuckenia striata (Ruiz et Pav.) Holub
2n = 78
855:A
RGENTINA, prov. Buenos Aires: irrigation canals in Bahía Blanca, provided by P. Denny in 1997, cult. &
coll. Z. Kaplan 855.
This species is closely related to S. pectinata and occurs in western and south-western
North America and South America. The chromosome count presented here is the first for
this species. Although the sample investigated morphologically fits the present concept of
456 Preslia 85: 421–482, 2013
S. striata, ITS sequencing indicated that this particular plant may be a hybrid rather than
a pure species (J. Fehrer, unpublished data). The relation between morphology, genetic
structure and taxonomy in Stuckenia requires further study.
Stuckenia vaginata (Turcz.) Holub
2n = 78
2052:R
USSIA, Siberia, Chita, distr. Uletovskiy: lake at Tanga, 50°58'07"N, 111°32'37"E, 8 VIII 2008, coll. S.
Rosbakh & K. Fleckenstein, cult. & coll. Z. Kaplan 2052.
2n = ca 78
1063:C
ANADA, Manitoba: inlet at northernmost large portion of Tramping Lake at start of Grass River, SE of
town of Snow Lake, 19 VIII 1998, coll. C. B. Hellquist & C. E. Hellquist, cult. & coll. Z. Kaplan 1063.
This species is circumboreal, distributed in northern Europe, northern Asia and northern
North America. The same count as we determined was published for Canada by Löve & Löve
(1961, 1981). Only an approximate number of 2n = ca 88 is reported for Sweden by Palmgren
(1939). Another count was published under an incorrect name. We examined the voucher
specimen (Löve & Löve 5260, DAO) for the chromosome count of 2n = 78 for “Potamogeton
pectinatus” given by Löve & Löve (1981) and found that it is actually Stuckenia vaginata.
Stuckenia ×bottnica (Hagstr.) Holub [= S. pectinata ×S. vaginata]
2n = 78
1027:D
ENMARK, Jylland (Jutland), region Syddanmark (Region of Southern Denmark): Sonderåstream at north-
ern edge of Rens, 54°54'00"N, 09°05'34"E, alt. 8 m, 19 VIII 1998, coll. Z. Kaplan 98/379, cult. & coll. Z. Kaplan
1027. – 1839 & 1840:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), distr. Alarskiy: Golumet’ River near
Nygda, ca 52°59'N, 102°40'E, 29 VIII 2006, coll. V. Chepinoga, cult. & coll. Z. Kaplan 1839 & 1840.
This hybrid is known from only a few boreal regions of the Northern Hemisphere. It is
here for the first time recorded for Denmark and Siberia. The chromosome count for this
hybrid is reported here for the first time.
Stuckenia ×fennica (Hagstr.) Holub [= S. filiformis ×S. vaginata]
2n = 78
1710: USA, Maine, Aroostook Co.: Prestile Stream just N of bridge on Pierce Road, Blaine, 1.5 km SSE of Mars
Hill, 46°29'45"N, 67°50'46"W, alt. 115 m, 2 VIII 2005, coll. Z. Kaplan & C. B. Hellquist 05/4358, cult. & coll.
Z. Kaplan 1710. – 2141:R
USSIA, Siberia, prov. Irkutsk (Irkutskaya oblast’), distr. Ziminskiy: Zima River at east-
ern edge of Ignay, 8.5 km S of Batama, 53°47'21.6"N, 101°37'31.6"E, alt. 479 m, 20 VIII 2009, coll. Z. Kaplan &
V. Chepinoga 09/367, cult. & coll. Z. Kaplan 2141.
2n = ca 78
1651: USA, Vermont, Addison Co.: fast flowing section of Otter Creek just at confluence with New Haven River
1 km W of Brooksville, Weybridge, 44°03'45"N, 73°10'39"W, alt. 67 m, 25 VII 2005, coll. Z. Kaplan & C. B.
Hellquist 05/384, cult. & coll. Z. Kaplan 1651.
This hybrid is known from only a few boreal regions of the Northern Hemisphere. The
samples investigated had the same chromosome number as their parental species. These
are the first chromosome counts for this hybrid.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 457
Stuckenia ×suecica (K. Richt.) Holub [= S. filiformis ×S. pectinata]
2n = 78
1009:S
WEDEN, prov. Södermanland: brackish water along sea shore at south-south-eastern edge of Dalarö,
ca 59°08'N, 18°25'E, 13 VIII 1998, coll. Z. Kaplan, cult. & coll. Z. Kaplan 1009.
The occurrence of this hybrid is only documented in several countries in the northern
half of Europe. Our chromosome count is the first made on this hybrid. It is the same as the
chromosome number of its parental species.
General discussion
Pattern of chromosome number variation
Chromosome numbers of 181 samples of 47 species and 32 hybrids were counted. In
Potamogeton, six cytotypes (2n = 26, 28, 39, 42, 52, 104) were identified in species and
seven cytotypes (2n = 26, 27, 39, 40, 52, 65, 78) in hybrids. The somatic numbers 26 and
52 predominated among species while counts of 39 and 42 were recorded for only two
species (a single plant in each, interpreted as autotriploids produced by diploid species, see
under P. compressus and P. pusillus for details). Les (1983) in his review indicates the fre-
quent occurrence of within-species variation in chromosome number in Potamogeton and
later Les & Scheridan (1990) suggest that extensive chromosome number modifications
have occurred within many modern species. Our observations do not support this view. In
contrast, our data indicate that within-species variation is very rare in Potamogetonaceae,
restricted to an exceptional rise of autotriploids. Similarly we did not detect any aneuploid
plants, although occurrence of aneuploids is recorded by some authors (Harada 1956,
Kalkman & Van Wijk 1984, Ceccarelli et al. 2008, Wan et al. 2012). The other two genera
were uniform, all taxa of Stuckenia shared the number 2n = 78 while the single species of
Groenlandia had 2n = 30. Our study provides the first chromosome counts for 10 species
and 25 hybrids of Potamogeton and for 1 species and 3 hybrids of Stuckenia, which fill
a considerable gap in the karyological data for this family. Nevertheless, for 33 of 80 spe-
cies of Potamogetonaceae (41%) there is no information on their chromosome numbers.
There are correlations between the variation in chromosome numbers identified in spe-
cies in the three genera of Potamogetonaceae and with eight basic morphological groups
in Potamogeton (see Table 1). The unique chromosome number of 2n = 30 exclusive to
Groenlandia densa supports its long-recognized separate generic position. Species with
2n = 78 are present only in Stuckenia, which is in accordance with the present treatment of
this group as a separate genus (Les & Haynes 1996, Holub 1997, Kaplan 2008). The
458 Preslia 85: 421–482, 2013
Table 1. – Chromosome numbers of species that were counted in this study and reported in the literature and their
relation to supraspecific groups (genera and basic morphological groups) in the Potamogetonaceae. Chromo-
some numbers recorded in this study that were based on multiple samples are given in bold.Sterile autotriploids
detected in two diploid fertile species were omitted (see text). The most frequently published chromosome num-
bers are given in bold, doubtful and unique recordsnot confirmed by other researchers are given in brackets. Erro-
neous records, mostly made on misidentified material, were excluded (for details see the text under particular
taxa). Literature records for P. cristatus and P. fryeri were taken from Takusagawa (1939, 1961), Harada (1942)
and Uchiyama (1989), for the remaining species see the text. ¤
Kaplan et al.: Chromosome numbers of Potamogetonaceae 459
Genus Informal species group
(in Potamogeton)
Species Chromosome
number determined
in this study (2n)
Literature records
(2n)
Groenlandia G. densa 30 30
Potamogeton I. linear-leaved species
(excl. P. compressus group)
P. berchtoldii 26 26
P. clystocarpus ca 26 –
P. foliosus 26 26 (28)
P. friesii 26 26
P. gemmiparus 26 –
P. groenlandicus 26 26
P. hillii 26 –
P. obtusifolius 26 26
P. ochreatus 26 –
P. oxyphyllus 26 26 (28)
P. pusillus 26 26
P. rutilus 26 26
P. strictifolius 26 –
P. trichoides 26 26
II. P. epihydrus group P. epihydrus ca 26 26
III. P. compressus group P. acutifolius 28 (26)
P. compressus 28 26, 28 (38–41)
P. zosteriformis 28 –
IV. P. diversifolius group P. spirillus 28 –
V. P. octandrus group P. octandrus 28 28
P. cristatus –28
VI. broad-leaved species
of the P. polygonifolius group
P. cheesemanii 28 28
P. coloratus 28 26
P. polygonifolius 28 26, 28
VII. majority of broad-leaved species P. alpinus 52 52
P. amplifolius 52 52
P. crispus 52 52 (26, 48, 50, 56, 78)
P. distinctus ca 52 52 (56)
P. fryeri –52 (42, 48)
P. gramineus 52 52
P. lucens 52 52
P. maackianus 52 52 (56)
P. natans 52 52 (42)
P. nodosus 52 52
P. perfoliatus 52 52 (78)
P. praelongus 52 52
P. richardsonii 52 52
P. robbinsii ca 52 52
P. sarmaticus 52 –
P. wrightii 52 52 (48, 50, 51)
VIII. broad-leaved species
of the P. illinoensis group
P. illinoensis 104 104
P. richardii ca 104 (42)
P. schweinfurthii 104 –
Stuckenia S. filiformis 78 78
S. pectinata 78 78 (70–87)
S. striata 78 –
S. vaginata 78 78 (ca 88)
remaining chromosome numbers occur in Potamogeton, the most species-rich genus of
the family. All counts of 2n = 52 and 2n = 104 are for broad-leaved species (groups VII and
VIII, respectively), the latter of which was identified only in three species for which our
preliminary molecular data revealed allopolyploid origins from different combinations of
broad-leaved species with 52 chromosomes (J. Fehrer & Z. Kaplan, unpublished data).
The count of 2n = 26 is confined to the linear-leaved species (group I) and to P. epihydrus
(group II). The number of 2n = 28 is characteristic of one group of linear-leaved species
(III), two groups of heterophyllous species (with broad floating leaves and linear sub-
merged leaves, groups IV and V) and one group of broad-leaved species (VI). Our counts
indicate that not only are species invariable in terms of chromosome numbers but also
whole basic morphological groups of Potamogetonaceae appear to be homogeneous in
this respect.
Additional support for the high regularity in the chromosome counts reported here
comes from the investigation of hybrids. All Stuckenia hybrids (8 counts for 4 hybrids)
had 78 chromosomes like their parents. For Potamogeton, 46 counts of different plants
were made that represented 29 hybrid combinations. The majority were homoploid
hybrids with 52 chromosomes like their parents (23 counts for 12 hybrids). Only in 4
cases, the hybrids between parents with 2n = 52 had 78 chromosomes, which was inter-
preted as a fusion of unreduced and reduced gametes. Two homoploid hybrids had 26
chromosomes like their parents. Heteroploid crosses usually had intermediate numbers of
chromosomes. Hybrids between 2n = 26 and 2n = 28 parents had 27 chromosomes (8
counts for 4 hybrids); hybrids with 2n = 78 were derived from crosses between parental
species with 52 and 104 chromosomes, respectively (4 counts for 4 hybrids); and for com-
binations in which one parent had 2n = 52 and the other had 2n = 26 or 2n = 28, the corre-
sponding 39 or 40 chromosomes were recorded (3 counts for 3 hybrids). The only
heteroploid cross that did not result in intermediate chromosome numbers was one of
a hybrid with 2n = 65, the parents of which had 52 and 26 chromosomes, respectively. In
this case, the former parent had apparently contributed an unreduced gamete.
Relatively regular patterns also emerged when the confirmed chromosome numbers
from Table 1 (doubtful ones excluded) were mapped onto phylogenetic trees based on
nuclear ribosomal markers (Figs 4 and 5). In most cases there was a close correspondence
between morphological groups, main clades and characteristic (or at least dominant) chro-
mosome number. This indicates a close relationship between chromosome number and the
systematic division of the family. Both Groenlandia and Stuckenia are separate
monophyletic lineages uniform in chromosome number (Fig. 4). Within Potamogeton
(Fig. 5), counts of 2n = 52 are confined to broad-leaved species, which all occur in a single
clade, while 2n = 26 occurs only among linear-leaved species and in the P. epihydrus
group. Species with 2n = 28 occur in several species-poor clades. Although not all main
clades are uniform in their chromosome number, nor are the morphological groups neces-
sarily monophyletic with this marker, the general pattern is far from random and shows
that there is actually very little variation in cytotypes within clades of Potamogetonaceae.
This is in strong contrast to previous studies (Les 1983, Les & Sheridan 1990,
Hollingsworth et al. 1998, Lindqvist et al. 2006) that attempted to identify trends in chro-
mosome number evolution in Potamogeton by assigning published chromosome counts to
phylogenetic trees or morphological groups. The elementary reason for their failure to
find any reasonably clear pattern is the high number of incorrect chromosome records
460 Preslia 85: 421–482, 2013
included in their data analyses. A review and critical evaluation of the published counts is
therefore an inevitable prior step to drawing evolutionary implications.
Reliability of published chromosome records and sources of errors
The main problems in cytotaxonomic studies are erroneous chromosome counts recorded
in the literature and incorrect identification of the plants studied (Stace 2000). As
karyological investigations are mostly conducted as independent studies of various
authors, a critical analysis of the previously obtained data is necessary (Guerra 2000,
Mansanares et al. 2002).
Kaplan et al.: Chromosome numbers of Potamogetonaceae 461
Fig. 4. – Phylogenetic analysis of the three genera of Potamogetonaceae based on ITS sequences. The Neighbor
joining tree is shown with bootstrap values above branches; bootstrap support for the Maximum parsimony analy-
sis (based on 239 parsimony informative characters incl. coded indels; resulting in 32 equally parsimonious trees
of length 413; ci=0.828; ri=0.948) is shown below branches; 100% support is indicated by an asterisk (*). For
Potamogeton, the main chromosome counts for the respective species are indicated in brackets. All tetraploid
species fall into the large clade at the bottom consisting of species with 26 or 28 chromosomes (data not shown).
For details about the accessions, see Appendix 1.
462 Preslia 85: 421–482, 2013
Literature review indicates extensive variation in chromosome numbers of
Potamogetonaceae. However, Hollingsworth et al. (1998) has already demonstrated that
many chromosome counts given in chromosome indices are erroneous and that some of
them were even never made. The comparison of our data, which show both a systematic
and phylogenetic pattern (see above), with that in the literature indicate that many of the
published records are highly doubtful. For example, Wiegand (1899) in his early study
records 2n = 14 for Potamogeton foliosus. However, this count has never been confirmed,
whereas there are six later counts of 2n = 26 for this species, which is consistent with the
number of chromosomes in all species in the respective morphological group (I in Table 1)
and with the numerous counts for closely related species with which P. foliosus forms
a strongly supported monophyletic clade (Fig. 5). Another example is P. perfoliatus,
which belongs to a morphological group of broad-leaved species (VII in Table 1) and also
to a highly supported clade (Fig. 5) where all closely related species have 2n = 52, which
can be considered as tetraploids. Thus, at least for significantly supported clusters com-
prising of several taxa with 52 chromosomes, speciation has taken place at the tetraploid
level. This is also in keeping with the general observation that direct sequence reads of ITS
and 5S-NTS of tetraploid species of Potamogeton (and hexaploid Stuckenia, see below)
do not show any indications of hybrid origin (in contrast to hybrids whose identifications
are based on the same markers). The count 2n = 52 for P. perfoliatus was established on 18
samples of this species. In addition, P. perfoliatus was involved in 8 different hybrids stud-
ied here all of which have karyotypes that are consistent with this chromosome number. In
the light of these observations, the existence of counts such as 2n = 26 recorded for
P. perfoliatus in the literature is highly improbable. A third example concerns the genus
Stuckenia. Our data indicate that all species (and hybrids) of this genus have 2n = 78
(Table 1), which can be considered as the hexaploid level within the Potamogetonaceae.
This is also the most frequently recorded number in the literature. The ITS tree (Fig. 4)
shows that Stuckenia forms a separate lineage and that speciation in this genus took place
entirely at the hexaploid level. Singular anomalous counts such as 2n = 42 recorded for
S. pectinata are therefore considered here as erroneous. Many other dubious and obvi-
ously incorrect records are discussed above under the particular species. It should be noted
that the majority of the doubtful counts come from only a few authors. Generally speak-
ing, all solitary unusual counts not confirmed by other researchers should be treated with
caution, particularly if other authors repeatedly record a different number.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 463
£Fig. 5. – Phylogenetic analysis of diploid and tetraploid species of Potamogeton based on 5S-NTS sequences.
One of 30 equally parsimonious trees is shown (based on 265 parsimony informative characters incl. coded
indels; tree length 1097; ci=0.500; ri=0.869) with bootstrap support above branches; posterior probabilities from
Bayesian analysis are given below branches. Confidence values of 100% / 1.00 are indicated by asterisks (*).
Chromosome numbers of particular species are given in different colours; the number for P. sibiricus was inferred
from the hybrid origin of the sample of P. groenlandicus analysed (see text); the individuals that had their chro-
mosomes counted in this study are in bold. Species names in black indicate that currently there are no known
chromosome numbers for these species. Assignments of morphological species groups correspond to Table 1.
A and B designate species-rich clades that are characterized by basal polytomies, which may indicate rapid
speciation. For details about the accessions, see Appendix 1.
The chromosomes of Potamogetonaceae are very small, often dot-like, ranging from
ca. 0.8–2 μm in length. Their size frequently differs even within a single cell and the small-
est may be less than a half of the size of the biggest. In diploid linear-leaved species (see
comments under P. acutifolius,P. berchtoldii,P. compressus,P. foliosus and P. pusillus)
we observed an occasional occurrence (i) of satellites on big chromosomes, which are usu-
ally approximately of the same size as the smallest chromosomes (Figs 1i & 3a–e) and (ii)
of massive chromosomes with conspicuous centromeres (Figs 3b & e). Particularly in the
case of rupture of these unusually shaped big chromosomes or of separation of the satel-
lites during preparation, these detached bodies can be easily misinterpreted by an
unexperienced eye as additional chromosomes in a karyotype with 2n = 26. In contrast,
two of the small chromosomes in a sample with 2n = 28 may be overlooked in low quality
preparations. Several species for which we identified 2n = 28 were previously treated as
species with 26 chromosomes and vice versa, which may be to a large degree explained by
technical difficulties caused by the karyotype. To establish exact chromosome numbers at
higher ploidy levels is even more difficult. The very small and rather numerous chromo-
somes, which greatly increases the potential for making errors during counting, stimulated
many authors to comment that Potamogeton is a genus difficult to investigate cytologi-
cally (e.g. Kalkman & Van Wijk 1984, Hollingsworth et al. 1998, Preston et al. 1998,
Wang et al. 2007, Wan et al. 2012). Thus, distinguishing genuine variation in chromosome
numbers from artefacts is particularly difficult in this family (Hollingsworth et al. 1998).
Only repeated observations of several clear well-spread metaphase preparations can pro-
vide unambiguous counts. In the light of this experience we are sceptical about the
recorded occurrence of aneuploid variation and the potential to distinguish actual
aneuploids from inexact interpretations of inadequate cytological preparations. Several
samples that we suspected at first to be aneuploids proved to be euploids in repeated obser-
vations of the same material. In spite of the factthat we studied 242 samples in great detail
(see Material and methods), we did not detect any unequivocally aneuploid plants.
The Potamogetonaceae are taxonomically difficult and our studies of herbarium mate-
rial indicate frequent misidentifications, sometimes even with phenotypically similar
plants of other families (such as Callitrichaceae,Zannichelliaceae,Polygonaceae and
Hydrocharitaceae). Unfortunately, we were not able to examine voucher specimens for
the majority of the doubtful records (for many records no vouchers were indicated and
may not even have been prepared; for others the vouchers are not available on loan from
the respective herbaria, especially from institutions in Asia), but those few herbarium
vouchers that we could inspect revealed several incorrectly identified specimens (see
under Potamogeton alpinus,P. polygonifolius,P. zosteriformis,Stuckenia pectinata and S.
vaginata). These cases are probably not exceptional, but may represent the tip of an ice-
berg. Chromosome counts recorded from continents where the respective species are
unknown to occur (see under Potamogeton compressus and P. rutilus for examples) indi-
cate additional taxonomic confusions. A further source of mistakes is the misidentification
of interspecific hybrids as species. Hybrids are in some regions more common than previ-
ously assumed (Kaplan 2005a, 2007, 2010a, Kaplan et al. 2009, 2011, Zalewska-Gałosz et
al. 2009, Du et al. 2010, Kaplan & Uotila 2011, Zalewska-Gałosz & Ronikier 2012,
Kaplan & Fehrer 2013) and their identification is often very difficult and may require the
aid of molecular techniques (Kaplan et al.2009, 2011, Zalewska-Gałosz & Ronikier 2010,
2011, Kaplan & Fehrer 2011, 2013). It is therefore possible that some doubtful counts
464 Preslia 85: 421–482, 2013
recorded for species were actually established on unrecognized hybrid plants. This is sup-
ported by the fact that some chromosome numbers reported in the literature for species (2n
= 27, 40, 65) were confined to hybrids in this study.
Some counts, although published as exact, may actually have been only estimated to fit
previously published records rather than counted. This is illustrated by P. polygonifolius.
Although three older records independently indicated 2n = 26, recent careful examination
of samples from four populations conducted by two different teams in different countries
gave unambiguous counts of 2n = 28. These were indirectly supported by two heteroploid
hybrids whose intermediate chromosome numbers showed that the second parent must
have had a karyotype with 28 chromosomes (see under P. polygonifolius for details). We
suspect that the former counts were only approximate, established on the mistaken belief
in the older literature that all Potamogeton diploids have 2n = 26. The case of one sample
of “P. alpinus” from Spain (see the discussion under P. polygonifolius above) clearly
shows that the temptation to fit actual observations to expected chromosome counts may
sometimes be high. In order to exclude this type of error a priori, our counts for this study
were mostly conducted without prior knowledge of the identity of the karyotyped plants
(see Methods).
In summary, the chromosome counts established by this study in combination with
a critical and thorough analysis of the original literature indicate that the within-species
variation in chromosome number is much lower than one would expect from the published
records. Based on the available data, we estimate that about 24% of the chromosome
records published for Potamogetonaceae in original publications and up to about 41% of
the records listed in secondary chromosome compilations (chromosome atlases and indi-
ces) are erroneous. Only when these erroneous records are filtered out to minimize the risk
of misleading conclusions, will the resulting reliable and confirmed data be suitable for
drawing evolutionary implications.
Chromosome base number and evolution of chromosome number
The identification of the base chromosome number is fundamental for understanding the
ploidy level of its members and the relationships between them. There is currently no con-
sensus on the base number in Potamogetonaceae. As Lindqvist et al. (2006) point out,
varying classification, incorrect identification of plants, technical difficulties in counting
small chromosomes and use of misleading sources of chromosome counts are the poten-
tial problems in studies on chromosome evolution in Potamogetonaceae.
Stern (1961) and Haynes (1974) have interpreted the chromosome numbers 2n = 26 or
28 to represent the diploid level in Potamogeton, from which one has been derived by
aneuploidy. In contrast, Goldblatt (1979) suggested that the base number in
Potamogetonaceae is likely to be x = 7. This is accepted by Les (1983) who also recog-
nizes 2n = 14 as the diploid level in Potamogeton. The main reason for this conclusion is
the record of 2n = 14 for P. foliosus by Wiegand (1899). In this concept, however,
P. foliosus would be the only extant diploid species in the family, all other species would
be polyploids and the count 2n = 26, which is the number recorded in approximately 36%
of Potamogeton species, would correspond to the hypotetraploid level. However, this old
record has never been confirmed and is here considered as erroneous (see under P. foliosus
for details). There is only one more record of n = 7 in Potamogetonaceae, which comes
Kaplan et al.: Chromosome numbers of Potamogetonaceae 465
from an early study by Takusagawa (1939) of P. perfoliatus. This count is even more
improbable considering the fact that P. perfoliatus belongs to a group of tetraploid (2n =
52) species (see also the discussion above). In the light of these data, x = 7 as the base num-
ber in Potamogeton is unsubstantiated.
The great majority of our counts are multiples of x = 13, which occurs in about 81% of
all species and in two of the three genera, Potamogeton and Stuckenia. Consequently,
plants with 26, 39, 52, 78 and 104 somatic chromosomes would correspond to diploids,
triploids, tetraploids, hexaploids and octoploids, respectively. In Potamogeton, diploids
with 2n = 26 and tetraploids with 2n = 52 are the most frequent as they occur in altogether
78% of the species analysed. The secondary number x = 14 occurs only within
Potamogeton where it is confined to four species-poor groups (III–VI in Table 1). If x = 13
is considered to be the base chromosome number, according to Fig. 5, about 3–7 inde-
pendent origins of x = 14 through aneuploid events from species with x = 13 have to be
assumed (exact estimates of such transitions cannot be made based on the tree, because the
relationships among the basal lineages within clades A and B are largely unresolved). Our
observations of two additional satellites of the size of normal chromosomes in several dip-
loid species with 26 chromosomes may give a hint how such transitions could have hap-
pened in the past. Groenlandia is unique with x = 15 and may have evolved from an ances-
tral x = 13 diploid through two such events. In contrast, Stuckenia may have originated
from a diploid ancestor by two subsequent rounds of polyploidization.
An alternative scenario of chromosome number evolution suggests 2n = 28 as the base
number. This view is supported by the fact that this count occurs in three of the most diver-
gent Potamogeton clades in both trees (Figs 4 and 5) and could therefore be viewed as the
relict ancestral constitution. Under this assumption, the transition from x = 14 to either x =
15 (Groenlandia) or to x = 13 (others) would require only one step in either direction. These
events could have resulted in reproductive isolation and may have triggered speciation and
polyploidization in various ways: Chromosome fusion in the lineage leading to Stuckenia
may have caused problems in meiosis that were overcome by immediate polyploidization
(in that case by two rounds, resulting in the hexaploid level) to restore fertility. Within
Potamogeton, two strongly supported species-rich clades (A and B in Fig. 5) are character-
ized by unresolved bases that suggest rapid speciation of the respective lineages. A single
transition to 26 chromosomes in clade A, a number which is now found in the majority of the
linear-leaved species, may have prompted extensive speciation, and incomplete lineage sort-
ing (e.g. Degnan & Rosenberg 2009, Krak et al. 2013) may explain the non-monophyletic
distribution of chromosome numbers within clade A. Similarly, an independent transition to
2n = 26 in clade B may have occurred in theancestor of the P. polygonifolius group (which is
identified as monophyletic using the ITS marker, see Fig. 4) and was followed by
polyploidization to the tetraploid level and by extensive speciation of the broad-leaved spe-
cies. A third transition to x = 13 then led to the P. epihydrus group.
As the chromosome number of P. confervoides, which constitutes another divergent
lineage within Potamogeton based on both markers (Figs 4 and 5), is unknown and too lit-
tle information about mechanistic pathways of chromosome fusion or fission in this group
is currently available, it is not possible at this point to draw definitive conclusions about
the base chromosome number of this family. However, we can clearly refute x = 7 as a base
number and establish x = 13 and x = 14 as the main diploid karyotypes in the family
between which multiple transitions must be assumed for each scenario. In addition, our
466 Preslia 85: 421–482, 2013
data clearly show that whole genome duplication is a rare event in Potamogetonaceae,in
contrast to some published chromosome records. It may have occurred only 2 (–3) times
during the evolution of Potamogetonaceae, once in the lineage leading to Stuckenia (Fig. 4)
and maybe only once early in the evolution of broad-leaved species of Potamogeton (clade
B in Fig. 5). A very low level of intra-individual polymorphism even in polyploid species
shows that ITS repeats are well homogenized, which also suggests ancient origins of
polyploidy (Kaplan et al. 2009). These can be readily distinguished from recent, but also
relatively rare, autopolyploidization events (2 cases), from occasional sterile addition
hybrids (5 cases) and from octoploid allopolyploid species (3 cases).
To conclude, chromosome numbers are generally uniform not only within species but
mostly also within morphological groups and clades. From this it is obvious that changes
in chromosome number, like aneuploidy and polyploidy, are rare in Potamogetonaceae
and mostly associated with major evolutionary events.
Descriptions of new hybrids
The samples counted included also several previously unknown interspecific hybrids,
which are recorded here for the first time. Besides morphology and molecular data, inter-
mediate chromosome numbers identified in heteroploid hybrids provided additional evi-
dence of their identities. Three of the hybrids that are sufficiently recognized and docu-
mented by adequate material are here described and their binomials validated. Detailed
results of molecular hybrid identifications will be presented in a separate paper (J. Fehrer
& Z. Kaplan, in prep.).
Potamogeton ×drepanoides Z. Kaplan, nothosp. nova
(= P. berchtoldii ×P. oxyphyllus)
Type: JAPAN, Honshu, Hiroshima Prefecture (Hiroshima-ken): water reservoir in Yamanaka park at University
campus SW of city centre of Higashi-Hiroshima, 34°24'12"N, 132°43'09"E, alt. 234 m (coll. L. Adamec 4 X
2000), cult. as Z. Kaplan 1238, pressed 1 VIII 2001 (holotype: PRA; isotypes: BM, GH, K, KRA, KYO, PR,
PRA, S, TI, W).
Stem richly branched, with long basal stolons producing new vertical shoots at nodes;
nodal glands present on most nodes; turions axillary, shoot-like but densely foliated,
35–67 mm long, with 8–13 leaves. Submerged leaves sessile, linear, often asymetrically
turned to one side, 34–92 mm long, 1.1–1.8 mm wide, 26–54 times as long as wide,
3-veined, sometimes with up to 6 inconspicuous and interrupted sclerenchymatous
strands, with 1–2 rows of lacunae on each side of the midrib, entire at margins, acute to
acuminate at the apex. Floating leaves absent. Stipules axillary, convolute, 7–11 mm long.
Inflorescences terminal; peduncle 13–28 mm long; spike 4–6 mm long. Flowers 3–5, with
4 abortive carpels. Fruits not produced (plants sterile). Fig. 6.
This hybrid resembles a slender narrow-leaved form of P. oxyphyllus, with which it was
originally confused until DNA analyses showed it to be a hybrid (J. Fehrer & Z. Kaplan,
unpublished data). The leaves are often asymetrically turned to one side, as in
P. oxyphyllus, whereas leaves of P. berchtoldii are ± strait or only dorsally recurved. The
venation of the leaves of the hybrid is more similar to that of P. berchtoldii as it shows only
3 veins, but sometimes they exhibit some inconspicuous and interrupted sclerenchyma-
tous strands, which are a vestige of often more numerous veins and sclerenchymatous
Kaplan et al.: Chromosome numbers of Potamogetonaceae 467
468 Preslia 85: 421–482, 2013
Fig. 6. – Holotype of Potamogeton ×drepanoides (= P. berchtoldii ×P. oxyphyllus).
strands that occur in leaves of typical broad-leaved plants of P. oxyphyllus. Turions of
P. ×drepanoides are less morphologically differentiated from normal shoots than those in
P. berchtoldii; they are longer, with numerous leaves, hence resembling short axillary
shoots, which is a feature that the hybrid shares with P. oxyphyllus. In contrast, turions of
P. berchtoldii are born terminally on the tops of shoots and branches, short, with only 2–4
short leaves, hence dissimilar from normal shoots. The hybrid also differs from both
parental species in being consistently sterile, like the great majority of Potamogetonaceae
hybrids (Hagström 1916, Dandy 1975, Preston 1995, Wiegleb & Kaplan 1998, Kaplan
2001, 2010a, Kaplan & Fehrer 2007, Kaplan et al. 2009).
Etymology: drepanoides = sickle-like, curved like a sickle; for sickle-shaped leaves
asymetrically turned to one side.
Additional specimens examined (paratypes): JAPAN, Honshu, Hiroshima Prefecture (Hiroshima-ken): water res-
ervoir in Yamanaka park at University campus SW of city centre of Higashi-Hiroshima, 34°24'12"N,
132°43'09"E, alt. 234 m (coll. L. Adamec 4 X 2000), cult. as Z. Kaplan 1238, pressed 27 VIII 2001 (PRA), 29
VIII 2002 (PRA), 23 VII 2003 (PRA), 21 VIII 2005 (PRA), 6 VIII 2007 (PRA), 30 X 2007 (PRA). – JAPAN, Hon-
shu, Hiroshima Prefecture (Hiroshima-ken): fishpond 1 km ENE of University campus SW of city centre of
Higashi-Hiroshima, 34°24'23"N, 132°43'47"E, alt. 227 m (coll. L. Adamec 4 X 2000), cult. as Z. Kaplan 1236,
pressed 1 VIII 2001 (PRA), 27 VIII 2001 (BM, GH, K, KRA, KYO, PR, PRA, S, TI, W), 29 VIII 2002 (PRA), 23
VII 2003 (PRA), 21 VIII 2005 (PRA), 6 VIII 2007 (PRA), 30 X 2007 (PRA).
Potamogeton ×luxurians Z. Kaplan, nothosp. nova
(= P. amplifolius ×P. illinoensis)
Type:USA, Vermont, Orleans Co.: Lake Parker1 km WSW of West Glover, 44°43'34"N,72°13'53"W, alt. 396 m,
22 VII 2005, coll. Z. Kaplan & C. B. Hellquist 05/362 (holotype: PRA; isotypes: GH, PRA).
Stem unbranched or sparingly branched. Submerged leaves subsessile to petiolate; lamina
oblong to broadly elliptical, sometimes slightly dorsally recurved, 55–188 mm long, 13–57
mm wide, 1.9–5.2 times longer than wide, 13–31-veined, apparently entire at margins or very
minutely denticulate on young leaves, with denticles fugacious and absent on older leaves,
acute to indistinctly mucronate or subobtuse at the apex; petiole 2–71 mm long, 0.02–0.64
times as long as the lamina. Floating leaves present on adult plants that reach the water surface,
petiolate; lamina oblong to elliptical, 72–145 mm long, 24–47 mm wide, 1.8–4.7 times as long
as wide, membranaceous to subcoriaceous or coriaceous, 17–33-veined, acute at apex; petiole
12–119 mm long, 0.1–0.8 times as long as the lamina. Stipules axillary, convolute, 17–93 mm
long. Inflorescences terminal; peduncle 36–193 mm long; spike 12–35 mm long. Flowers
numerous, with 4 abortive carpels. Fruits not produced (plants sterile). Fig. 7.
This hybrid is clearly intermediate between the parents, particularly in the shape and
size of submerged leaves. The lamina of thesubmerged leaves is on average narrower than
in P. amplifolius (25–75 mm wide, mostly 2–4 times longer than wide) but broader than in
P. illinoensis (mostly 10–40 mm wide, 4–8 times longer than wide). The lamina of sub-
merged leaves of P. illinoensis as well as of P. ×luxurians is ± strait or slightly dorsally
recurved whereas that of P. amplifolius is typically strongly arcuate. Another quantitative
character that shows intermediate values in P. ×luxurians is the number of veins in leaves.
The hybrid has fewer veins than P. amplifolius (mostly 25–37 in submerged leaves and
29–41 in floating leaves) but more numerous veins than P. illinoensis (mostly 7–17 in sub-
merged leaves and 13–29 in floating leaves). In contrast to the parental species, the hybrid
is sterile and its entire spikes rot after flowering instead of setting fruit.
Kaplan et al.: Chromosome numbers of Potamogetonaceae 469
470 Preslia 85: 421–482, 2013
Fig. 7. – Holotype of Potamogeton ×luxurians (= P. amplifolius ×P. illinoensis).
Etymology: luxurians = luxuriant, characterized by profuse growth; based on the
growth of plants in the type population.
Additional specimens examined (paratypes): USA, Vermont, Orleans Co.: Lake Parker 1 km WSW of West
Glover, 44°43'34"N, 72°13'53"W, alt. 396 m, cult. as Z. Kaplan 1625, pressed 7 IX 2006 (PRA), 27 VII 2007
(PRA), 26 VIII 2008 (PRA). – USA, Massachusetts, Berkshire Co.: small pond on north side of Thomas Island
Road at Lake Onota, Pittsfield, 42°28'52"N, 73°16'23.4"W, 18 VIII 2009, coll. C. B. Hellquist 17158 & J. Garrett
(PRA). – USA, Massachusetts, Franklin Co.: Leverett Pond, Leverett, 42°27.057'N, 72°30.137'W, alt. 417 ft., 18
VI 2009, coll. C. B. Hellquist 17117, A. Bobrov & E. Chemeris (PRA).
Hagström (1916) describes P. scoliophyllus as a hybrid P. amplifolius ×P. illinoensis
based on three collections. The first collection, from Michigan, USA, is preserved in S; its
duplicates (isosyntypes) are preserved in GH and NY. These plants are morphologically
consistent with P. illinoensis, the shape and size of leaves correspond to this species, as
well as the mucronate leaf apices and the numbers of veins in floating (15–17) and sub-
merged leaves (11). Also, the stem anatomy agrees with that of P. illinoensis. The two
remaining collections are from Canada and preserved in C. The specimen from Quebec is
rather typical P. illinoensis with 11–13-veined submerged leaves and that from Ontario
has submerged leaves with 11–17 veins and is also consistent with the morphology of
P. illinoensis. In fact, Hagström (1916) himself comments that his taxon is more similar
morphologically and anatomically to P. illinoensis than intermediate. The protologue indi-
cates that the plant from Michigan was the main basis for the description of the taxon; the
specimen was annotated by Hagström on 17th February 1900 and 9th October 1907, i.e.
prior to the publication of its name, its morphology is in agreement with the description
given in the protologue, and the specimen is therefore selected here for lectotypification of
the name (the herbarium sheet was labelled accordingly by ZK in 2007):
Potamogeton scoliophyllus Hagstr., Kungl. Svenska Vetenskapsakad. Handl. 55/5: 164. 1916.
Type: “Herb. Thomas Morong, Potamogeton lucens L., …, In lacu “Bar” ad Manistee,
Michigan, U.S.A., Leg. T. M[orong], Aug. 18, 1882” (lectotype: S, designated here).
Potamogeton ×serrulifer Z. Kaplan, nothosp. nova
(= P. crispus ×P. schweinfurthii)
Type: ITALY, Tuscany, prov. Siena: water reservoir 1.1 km ENE of San Fabiano farm, 1.6 km NE of Monteroni
d’Arbia, 43°14'33.7"N, 11°26'11.3"E, alt. 180 m, cult. as Z. Kaplan 1953, pressed 16 IX 2009 (holotype: PRA;
isotypes: BM, PRA).
Stem unbranched or rarely only sparingly branched above. Submerged leaves sessile,
linear-oblong to oblanceolate, (32–) 52–122 (–137) mm long, (4–) 6–10 (–14) mm wide,
(6–) 9–15 (–17) times longer than wide, 5–7-veined, very finely but distinctly undulate
along margins, denticulate to serrulate at margins, acute to shortly mucronate at apex. Float-
ing leaves absent. Stipules axillary, convolute, 9–20 (–41) long, acute, delicate, gradually
disappearing. Inflorescences terminal; peduncle 20–58 mm long; spike 9–15 mm long.
Flowers numerous, with 4 abortive carpels. Fruits not produced (plants sterile). Fig. 8.
At first sight, this hybrid resembles slender plants of P. schweinfurthii and it may be dif-
ficult to distinguish them. The typical robust plants of P. schweinfurthii mostly have longer
(up to 250 mm) and wider (up to 28 mm) leaves with more veins (mostly 7–9). While the
leaves of P. schweinfurthii are only minutely denticulate to almost entire at margins and
Kaplan et al.: Chromosome numbers of Potamogetonaceae 471
472 Preslia 85: 421–482, 2013
Fig. 8. – Holotype of Potamogeton ×serrulifer (= P. crispus ×P. schweinfurthii)
± flat, those of P. ×serrulifer are denticulate to serrulate at margins and finely but distinctly
undulate along margins, which are clearly characters inherited from P. crispus. The leaves
of P. ×serrulifer are more abruptly contracted to the apex than those of P. schweinfurthii,
which has leaves distinctly mucronate or acuminate at the apex. Stipules of the hybrid are
smaller, delicate and gradually disappear whereas those of P. schweinfurthii are more
robust (20–95 mm long) and persistent. The inflorescence of P. ×serrulifer is also smaller
than that of P. schweinfurthii, which has a 35–250 mm long peduncle and a 40–92 mm
long spike at fruiting. The other parent, P. crispus, can be easily distinguished by its linear
to linear-oblong leaves, which are serrate and usually strongly undulate at themargins, and
by its characteristic pattern of venation that is unlikely to be confused with that of any
other species. The leaves of P. crispus usually have two veins on each side of the midrib,
with the outer pair of veins being faint and running close along the margins and the inner
pair being more prominent and running longitudinally at approximately 1/2–2/3of the dis-
tance between the midrib and the margins. In contrast, the leaves of P. ×serrulifer have
veins more regularly and evenly spaced, like P. schweinfurthii. Further characters that dis-
tinguish P. crispus from the hybrid include small (4–12 mm long) and early decaying stip-
ules and a small number of flowers (3–8). In contrast to the parental species, the hybrid is
sterile and the entire spikes rot after flowering instead of setting fruit.
Etymology: serrulifer = bearing small serrations, finely serrulate; refers to the margins
of the leaves.
Additional specimens examined (paratypes): ITALY, Tuscany, prov. Siena: water reser-
voir 1.1 km ENE of San Fabiano farm, 1.6 km NE of Monteroni d’Arbia, 43°14'33.7"N,
11°26'11.3"E, alt. 180 m, 12 VIII 2008, coll. Z. Kaplan, L. Lastrucci, F. Frignani & B.
Foggi 08/612 (PRA); material from the type locality, cult. as Z. Kaplan 1953, pressed 27
VII 2009 (PRA), 10 VIII 2009 (PRA).
Acknowledgements
We are grateful to all the collectors cited in the text who provided us with plant material from distant areas, to Vic-
tor Chepinoga, C. Barre Hellquist, Lorenzo Lastrucci, Anders Svenson, Jitka Štěpánková and Pertti Uotila, for
their help during fieldwork, to Abdolreza Yadollahi and Veronika Bambasová for performing the molecular
labwork, to John Bailey for verification of our count of 2n = 28 for sample 950,to curators of the herbaria visited
who allowed us to study their collections and to curators Bruce A. Ford, Stuart G. Hay, Tim Hogan and Gisèle
Mitrow for searching for missing specimens in their herbaria. The research was supported by grant no.
206/09/0291 from the Czech Science Foundation and by the long-term research development project no. RVO
67985939 from the Academy of Sciences of the Czech Republic.
Souhrn
Karyologickou variabilitu v čeledi rdestovité (Potamogetonaceae) jsme podrobili revizi a zhodnotili z pohledu
taxonomie a evoluce. Pro 47 druhůa 32 kříženců pocházejících z různých koutů světa jsme stanovili chromozo-
mové počty, přičemž pro 11 druhů a 28 kříženců se jedná o první karyologické údaje. Tři poprvé rozpoznaní kří-
ženci jsou v článku platně popsáni. Dále jsme analyzovali literárníúdaje, mezi nimiž jsme zjistili poměrně velké
množství chyb. Naše pozorování nepotvrdila udávanou vysokou míru vnitrodruhové variability v počtu chromo-
zomů. Právě naopak, chromozomový počet u taxonů čeledi Potamogetonaceae se zdá být relativně stabilní znak,
který je specifický nejen pro jednotlivé druhy (výjimkou je pouzeojedinělý vznik sterilních autotriploidních rost-
lin v populacích fertilních diploidů), ale i pro celé skupiny druhů, a do jisté míry i pro celé klady ve fylogenetické
rekonstrukci. Druhově nejbohatší rod Potamogeton obsahuje dvě základní čísla (x = 13 a x= 14) a druhy na třech
Kaplan et al.: Chromosome numbers of Potamogetonaceae 473
ploidních úrovních (diploidy, tetraploidy a oktoploidy; všechny polyploidní cytotypy jsou odvozeny od počtu x =
13). Rod Stuckenia zahrnuje výhradně hexaploidy (rovněž odvozené od x = 13) zatímco monotypický rod Groen-
landia se vyznačuje unikátním základním chromozomovým číslem x = 15. Na základě revidovaných počtů chro-
mozomů a fylogenetické analýzy jsme se pokusili identifikovat základní chromozomové číslo a evoluci karyoty-
pu. Předložili jsme dva alternativní scénáře evoluce čeledi, se základním chromozomovýmčíslem x = 13 nebo x =
14, přičemž každý předpokládá několik aneuploidních změn mezi těmitokaryotypy a jednu změnu k číslu x = 15.
Hypotéza některých autorů, kteří pokládají za základní číslo x = 7, byla založena na mylných předpokladech a je
zde odmítnuta. Zásadní změny genomu jako jsou aneuploidie a polyploidie jsou většinou svázány s významnými
evolučními událostmi. Skupina tetraploidů v rodu Potamogeton vznikla jako důsledek jedné nebo několika málo
polyploidizací, zatímco dvě následné polyploidizace vysvětlují vznik rodu Stuckenia, kde se veškerá speciace
odehrála na hexaploidní úrovni. Tři oktoploidní druhy rodu Potamogeton jsou alopolyploidního původu.
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Received 24 June 2013
Revision received 26 August 2013
Accepted 26 August 2013
480 Preslia 85: 421–482, 2013
Appendix 1. – Origin of the accessions used in the molecular analyses and their GenBank accession numbers.
Reference numbers in bold indicate that the chromosomes of that particular sample were counted. Some ITS data
are from our previous publications; accession numbers KF270900–KF271010 are new for this study. For
P. groenlandicus 5S-NTR, two cloned sequences corresponding to the parental species are given. Sequences of
P. cristatus were adopted from GenBank.
Species Country Reference number
/ Isolate
GenBank accession numbers
ITS 5S-NTS
G. densa Switzerland 970 KF270900
Austria 988 KF270901
P. acutifolius Czech Republic 321 KF270902 KF270930
Sweden 2131 KF270931
P. alpinus Czech Republic 1537 KF270932
Russia 2470 KF270933
P. amplifolius USA 1689 KF270934
USA 2282 KF270935
P. berchtoldii Russia 174 KF270936
Czech Republic 930 KF270903 KF270937
USA 1641 KF270938
Japan 1848 KF270939
P. bicupulatus USA 1627 FJ151203 KF270940
USA 1680 KF270941
P. cheesemanii New Zealand 950 KF270942
New Zealand 1070A KF270904 KF270943
P. clystocarpus USA 1671 KF270944
P. coloratus Austria 1545 HQ263487 KF270945
P. compressus Sweden 1012 KF270946
Russia 2049 KF270905 KF270947
P. confervoides USA 1670 KF270906 KF270948
USA 1737 KF270949
P. crispus Czech Republic 1463 KF270950
South Korea 2337 KF270951
P. cristatus FJ495503
FJ495504
China JF977889
P. distinctus India 2675 KF270952
P. epihydrus USA 1635 FJ151206 KF270953
USA 2216 KF270954
P. foliosus USA 1608 KF270907 KF270955
USA 1994 KF270956
P. friesii USA 1658 KF270908 KF270957
P. fryeri Japan 1234 KF270958
P. gemmiparus USA 1696 KF270909 KF270959
P. gramineus Czech Republic 885 KF270960
Czech Republic 897 KF270961
France 1156 KF270962
France 1285 KF270963
‘P. groenlandicus’
= P. sibiricus × P. berchtoldii
Greenland 1153 KF270964 (sib)
KF270965 (ber)
P. hillii USA 1607 KF270910 KF270966
P. lucens Netherlands 858 KF270967
Japan 1762 KF270968
P. maackianus China 1570 KF270969
Japan 1768 KF270970
P. natans Switzerland 977 KF270971
Hungary 2379 KF270972
Kaplan et al.: Chromosome numbers of Potamogetonaceae 481
P. nodosus France 1309 KF270973
USA 2207 KF270974
P. oakesianus USA 1628 KF270975
P. obtusifolius Canada 1051 KF270976
Denmark 2567 KF270911 KF270977
P. ochreatus New Zealand 1071 GU814250 KF270978
Australia 2214 KF270979
P. octandrus Japan 1915 KF270912 KF270980
P. oxyphyllus Japan 1765 KF270913 KF270981
P. perfoliatus Austria 985 KF270982
USA 1626 KF270983
P. polygonifolius Czech Republic 1533 HQ263525 KF270984
P. praelongus Germany 881 KF270985
Italy 1530 KF270986
P. pulcher USA 1681 KF270987
P. pusillus Czech Republic 1159 KF270988
USA 1712 KF270914 KF270989
P. richardsonii Canada 1056 KF270990
USA 2316 KF270991
P. robbinsii USA 1596 KF270992
USA 1667 KF270993
P. rutilus Finland 2115 KF270915 KF270994
P. sarmaticus Russia 1917 KF270995
Russia 1918 KF270996
P. sibiricus Russia 2493 KF270916 KF270997
Russia 2494 KF270998
P. spirillus USA 1632 FJ151214 KF270999
USA 1695 KF271000
P. strictifolius USA 1707 KF270917 KF271001
P. suboblongus New Zealand 2553 KF270918 KF271002
P. trichoides Czech Republic 1903 KF271003
India 2668 KF270919 KF271004
P. vaseyi USA 1697 KF270920 KF271005
USA 2198 KF271006
P. wrightii Japan 1239 KF271007
Japan 1759 KF271008
P. zosteriformis Canada 1491 KF270921 KF271009
USA 1591 KF271010
S. amblyphylla Tajikistan 2602 KF270922
Tajikistan 2603 KF270923
S. filiformis Switzerland 1187 KF270924
USA 1703 KF270925
S. pectinata USA 1650 KF270926
India 2026 KF270927
S. vaginata USA 1976 KF270928
Russia 2141 KF270929
482 Preslia 85: 421–482, 2013
