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Occurrence of sclerenchymatous strands in leaves of Potamogeton. a, P. ×jacobsii (Hellquist 17201 & Sainty); b & c, P. ochreatus (Kaplan 1071). Scale bar identical for all figures: 1 mm.
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Although more than 80 hybrids are documented for Potamogeton in the Northern Hemisphere, the hybrid diversity in the Southern Hemisphere is largely unknown. A taxonomically uncertain Potamogeton plant discovered in New South Wales, Australia, was subjected to detailed morphological investigation and molecular analyses to discover its exact identity...
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... along the margins and the inner pair being more prominent and running longitudinally at approximately ½-⅔ of the distance between the midrib and the margins (Fig. 2a). This venation pattern can be observed also in P. ×jacobsii (Fig. 2b), but some leaves contain also faint and irregular sclerenchymatous strands in addition to the vascular veins (Fig. 3a), which is clearly a character inherited from P. ochreatus, the only Australian species showing this structure (Fig. 3b). The leaves of P. ×jacobsii are also similar to those of P. crispus in size, resembling narrow-leaved forms of this species (Figs 4a & 4b), but in the hybrid they are often truncate or slightly retuse at the apex ...
Context 2
... between the midrib and the margins (Fig. 2a). This venation pattern can be observed also in P. ×jacobsii (Fig. 2b), but some leaves contain also faint and irregular sclerenchymatous strands in addition to the vascular veins (Fig. 3a), which is clearly a character inherited from P. ochreatus, the only Australian species showing this structure (Fig. 3b). The leaves of P. ×jacobsii are also similar to those of P. crispus in size, resembling narrow-leaved forms of this species (Figs 4a & 4b), but in the hybrid they are often truncate or slightly retuse at the apex (Figs 4c & 4d), and thus more similar to that of P. ochreatus (Figs 4e & 4f). Hybrids of P. crispus often differ from their ...
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Citations
... Recent studies on Potamogeton show that even in relatively well explored areas such as Europe or North America, the origin of the observed variation is poorly understood, and a great deal of the diversity is neglected and remains undetected [11][12][39][40]. Molecular analyses have recently contributed to elucidate the systematic position of taxonomically uncertain local forms [15,41], the discovery or exact identification of several entirely new hybrid combinations [11, 40,[42][43][44][45][46] and even confirmed the existence of a triple hybrid in Potamogeton [47]. ...
Thorough understanding of biodiversity is a fundamental prerequisite for biological research. A lack of taxonomic knowledge and species misidentifications are particularly critical for conservation. Here we present an example of Potamogeton floridanus, the Florida Pondweed, an endangered taxon endemic to a small area in the Florida panhandle, whose taxonomic status remained controversial for more than a century, and all previous attempts to elucidate its identity have failed. We applied molecular approaches to tackle the origin of the mysterious taxon and supplemented them with morphological and anatomical investigations of both historical herbarium collections and plants recently collected in the type area for a comprehensive taxonomic reassessment. Sequencing of two nuclear ribosomal markers and one chloroplast non-coding spacer resulted in the surprising discovery that P. floridanus is a hybrid of P. pulcher and P. oakesianus, with the former being the maternal parent. The hybrid colony is currently geographically isolated from the distribution range of P. oakesianus. We show that previous molecular analyses have failed to reveal its hybrid identity due to inadequate nuclear DNA sequence editing. This is an example how the uncritical use of automized sequence reads can hamper molecular species identifications and also affect phylogenetic tree construction and interpretation. This unique hybrid taxon, P. ×floridanus, adds another case study to the debate on hybrid protection; consequences for its conservation are discussed.
... The main sources of taxonomic complexity include the reduced morphology, which limits the number of taxonomic characters that can be used to separate species (Preston & Croft, 1997;Kaplan & Štěpánek, 2003; Recent studies on Potamogeton taxonomy have concentrated mainly on the occurrence and diversity of hybrids (e.g. Preston, Bailey & Hollingsworth, 1998;Kaplan, 2001aKaplan, , 2005aKaplan, , 2007Kaplan et al., 2002Fant, Kamau & Preston, 2003;Kaplan & Fehrer, 2004Kaplan & Wolff, 2004;Kaplan & Zalewska-Gałosz, 2004;Zalewska-Gałosz, Ronikier & Kaplan, 2009Kaplan, Fehrer & Hellquist, 2011;Kaplan & Uotila, 2011). Only a few studies have recently dealt with the morphological delimitation of species (e.g. ...
The Potamogeton compressus group is a complex of three to five closely related species with a circumpolar distribution in the Northern Hemisphere. Multivariate morphometric analyses (principal component analysis, cluster analysis, canonical and classificatory discriminant analyses) were used to elucidate patterns in variation within this group and to test morphological differentiation of the respective species recognized in the current literature. 156 specimens from the entire distribution range of the group were included in the numerical methods. Results from morphological comparison are discussed in relation to molecular data, reproductive behaviour and geographic distribution. Morphometric analyses provided evidence that this complex can be clearly divided in three groups; one of them was subdivided based mainly on allopatric occurrence and genetic differentiation. These groups correspond to four here accepted species: P. acutifolius (temperate regions of Europe), P. compressus (boreal and temperate regions of Europe and Asia), P. manchuriensis (northeastern China and Russian Far East) and P. zosteriformis (boreal and temperate regions of North America). Two of them, P. acutifolius and P. compressus, are partly sympatric but perfectly differentiated morphologically and genetically, and effectively isolated reproductively. Endemic P. manchuriensis is characterized by a unique combination of characters and an occurrence in a limited geographical area. Allopatric P. zosteriformis is weakly differentiated morphologically from P. compressus but differs markedly by molecular markers correlated with geographical differentiation, and may thus represent a cryptic species. In contrast, a recently suggested concept of southern Siberian P. henningii was not supported by our analyses. Plants so named are considered here as slender phenotypes of the widespread and variable P. compressus.
... Ogden 1943, Haynes & Williams 1975, Brayshaw 2000, Alix & Scribailo 2006), Siberia (Kashina 1988, Chepinoga et al. 2008), China (Wiegleb 1990a, Wang et al. 2007, Du et al. 2009) and Japan (Miki 1937, Kadono 1983, Kadono & Wiegleb 1987, Ito et al. 2007, Iida & Kadono 2002). Only recently a Potamogeton hybrid was identified also in the Southern Hemisphere, in Australia (Kaplan et al. 2010). The number of identified and now recognized Potamogetonaceae hybrids has increased to 86 (Z. ...
A revision of the diversity and distribution of Potamogeton hybrids in the Czech Republic is presented. Thorough examination of herbarium material and recent extensive field studies revealed the present and/or past occurrence of eight Potamogeton hybrids in the Czech Republic. In addition to morphological characters, stem anatomy and/or molecular analysis were used to identify some of the hybrids. All the hybrids detected are between broad-leaved species of the genus, suggesting that hybrids between linear-leaved species may be overlooked because of the overall morphological similarity of taxa within this group. Four of the hybrids identified, P. ×nitens, P. ×olivaceus, P. ×sparganiifolius and P. ×undulatus, are recorded for the first time from the Czech Republic. Four of the hybrids are now extinct in the Czech Republic and the extant hybrids are rare. The occurrence of P. ×lintonii was not confirmed; the previous record was based on extreme forms of P. gramineus. The name P. ×concinnitus, proposed for a putative hybrid combination “P. pusillus × P. crispus”, was lectotypified and reduced to a synonym of P. crispus. Although the absolute number of finds of specimens of Potamogeton hybrids per decade is increasing, this is not a result of more frequent hybridization but of an increase in recording activity. Most records for recent decades are associated with targeted research by a few experts. The typical habitat of Potamogeton hybrids in the Czech Republic are ponds that were previously drained in summer and allowed to dry out. Many historical localities disappeared when the traditional fishpond management was largely abandoned and fish farming become more intensive. In the 19th century in particular some hybrids were recorded also in rivers but these occurrences generally disappeared after the extensive channelling of rivers at the beginning of the 20th century. Many hybrids occur at the same localities as their parents but it is documented that hybrids can persist vegetatively in the absence of the parental species, presumably as relics of the previous presence of the parent plants. Although almost all Potamogeton hybrids are consistently sterile, a cultivation experiment showed that P. ×angustifolius set seeds that were fertile and successfully produced adult plants.
Potamogetonaceae are aquatic plants divided into six genera. The largest genus in the family is Potamogeton, which is morphologically diverse with many hybrids and polyploids. Potamogetonaceae plastomes were conserved in genome size (155,863 bp–156,669 bp), gene contents (113 genes in total, comprising 79 protein-coding genes and 30 tRNA and 4 rRNA genes), and GC content (36.5%). However, we detected a duplication of the trnH gene in the IR region of the Potamogeton crispus and P. maakianus plastomes. A comparative analysis of Alismatales indicated that the plastomes of Potamogetonaceae, Cymodaceae, and Ruppiaceae have experienced a 6-kb inversion of the rbcL-trnV region and the ndh complex has been lost in the Najas flexilis plastome. Five divergent hotspots (rps16-trnQ, atpF intron, rpoB-trnC, trnC-psbM, and ndhF-rpl32) were identified among the Potamogeton plastomes, which will be useful for species identification. Phylogenetic analyses showed that the family Potamogetonaceae is a well-defined with 100% bootstrap support and divided into two different clades, Potamogeton and Stuckenia. Compared to the nucleotide substitution rates among Alismatales, we found neutral selection in all plastid genes of Potamogeton species. Our results reveal the complete plastome sequences of Potamogeton species, and will be helpful for taxonomic identification, the elucidation of phylogenetic relationships, and the plastome structural analysis of aquatic plants.
Aquatic plant species are often widespread, even across continents. They pose a challenge to species delimitation and taxonomy due to their reduced morphology and high phenotypic plasticity. These difficulties are even more pronounced in the case of interspecific hybridization. We investigate the aquatic plant genus Stuckenia for the first time on a worldwide scale. Expert species determination is aided by sequencing of nuclear ribosomal ITS and 5S-NTS regions and the plastid intergenic spacers rpl20-5’rps12 and trnT–trnL. Nuclear markers are used to infer hybridization, and the maternal origin of hybrids is addressed with plastid markers. Pure species are subjected to phylogenetic analyses. Two main Stuckenia lineages are found: one consists of S. amblyphylla, S. filiformis, S. pamirica, and S. vaginata, the other includes S. pectinata and S. striata. The widespread species S. pectinata, S. filiformis, and S. vaginata show intraspecific genetic variation, which is structured geographically. Many intraspecific hybrids, which are usually fertile, occur between those genotypes. Interspecific hybrids, which are consistently sterile, are detected among all widespread species; some are reported for the first time in several countries and regions. They originated multiple times from reciprocal crosses and reflect the geographical origins of parental genotypes. Intraspecific genetic variation can be higher than interspecific differences between closely related species. Comparison of phenotypic variation in the field and in cultivation with genotypic variation shows that numerous conspicuous forms have been overestimated taxonomically. These are resolved as phenotypes responding to unusual environments, have recurrently evolved adaptations, or represent extreme forms of continuous variation of the recognized species. However, some specific regional lineages, which have evolved from variable species, may be interpreted as early steps of the speciation process. Hybridization has been underestimated in some regions as a source of Stuckenia diversity, and the respective hybrid plants have been misidentified as intraspecific taxa or even as separate species. Many erroneous entries in sequence databases are detected and summarized. This work provides a sound basis for species delimitation and hybrid recognition in this difficult genus.
Cryptic species are morphologically indistinguishable but genetically divergent entities that constitute an important part of Earth's biodiversity. They occur in all kingdoms of life, especially when morphological characters are scarce. Compared to the high number of plant species, relatively few cryptic species have been detected so far. Here, we report cryptic species in pondweeds (Potamogeton), freshwater aquatic angiosperms that are characterized by reduced morphology. Using four molecular markers (ITS, 5S‐NTS, rpl20‐5′rps12, trnT‐trnL), three of them unlinked, we found that the widespread P. octandrus consists of three divergent lineages that correspond to the geographic origins of samples from Africa, Asia, and Australia, respectively. Relatively high genetic divergence between these lineages, reciprocal monophyly and many fixed diagnostic characters indicate that P. octandrus consists of three cryptic species. We formally distinguish the African lineage as P. parvifolius and the Australian lineage as P. tenuicaulis from Asian P. octandrus s.str. Potamogeton tenuicaulis is paraphyletic with the Asian species P. cristatus, which differs by unique fruit characters. We assume that the ancestor of P. cristatus originated from Australia and reached Asia by long‐distance dispersal. Quality criteria for assigning species status to cryptic species and their formal taxonomic recognition are discussed.
The family Potamogetonaceae has been taxonomically re‐evaluated in Turkey, employing traditional morphological as well as molecular approaches (rbcL, ITS). Our fieldwork, herbarium studies and molecular analyses proved the existence of 22 taxa, of which 18 belong to Potamogeton (including 4 interspecific hybrids), 3 to Stuckenia and 1 to monotypic Groenlandia. Morphological re‐descriptions of the recognized taxa were prepared, and the information concerning their distribution in Turkey was refined, based on plant material from extensive fieldwork and on specimens stored in herbaria that were previously not examined. Additionally, new identification keys to genera and species, and distribution maps of the species were prepared. Phylogenetic relationships and intraspecific variations were assessed by including samples from other regions. The status of the Zannichelliaceae was investigated using nuclear and chloroplast DNA markers. Our results from ITS sequence divergence corroborate the separation of the two families noted by some authors, and are in accordance with the substantial morphological differences between them. Relatively large genetic distance and non‐monophyly indicate that two genotypes of P. gramineus constitute cryptic species, for which the Turkish localities expand upon the previously known distribution areas. We identified P. schweinfurthii as a new species for Turkey and report P. ×angustifolius for the first time for this country. Weak morphological differentiation and high sequence similarity did not permit reliable differentiation between the closely related Stuckenia amblyphylla and S. filiformis.
The interspecific hybrid Potamogeton ×salicifolius (= P. lucens × P. perfoliatus), so far known only from several countries of Europe and a few countries of Asia, was discovered in Western Australia. Morphology of the Australian specimens fits the range of variation observed in Eurasian specimens. DNA sequencing confirmed the morphological identification as a hybrid P. lucens × P. perfoliatus, and identified P. lucens as the maternal parent. This identity is surprising because neither of the parental species are known to occur in Western Australia and P. lucens currently does not even occur in the continent. Three possible explanations for the occurrence of P. ×salicifolius in Western Australia are discussed: its relictual occurrence from a time when both the parental species occurred there, long-distance dispersal of a hybrid seed from Eurasia and the remnant of local cultivation or intentional planting.
Hybrids form an important component of Potamogeton diversity but their exact taxonomic identities and distributions are often insufficiently known. Potamogeton nerviger was described from Lithuania in 1827 as a proper species. Based on morphological and anatomical characters, its interpretation has since varied, ranging from synonymization with other species to identification as different hybrids and intraspecific taxa. Currently, it is universally recognized as the hybrid P. alpinus × P. lucens. Using a combined molecular, morphological and anatomical investigation we re-examined the identity of P. ×nerviger, based on both original and recent plant material. We report a successful amplification and sequencing of nuclear ribosomal ITS1 region from a 188-year-old type collection. This was shown to be genetically identical to the morphologically matching plants recently collected at the type locality. Comparison with molecular characters of the possible parental species shows that P. ×nerviger is not P. alpinus × P. lucens, as currently believed, but another hybrid, P. nodosus × P. perfoliatus, which is currently called P. ×assidens. This molecular identification is also supported by anatomical evidence. In contrast, the actual existence of the hybrid P. alpinus × P. lucens is doubtful. Consequences for nomenclature and identities of records reported from other sites are discussed.
Hybridization is an important source of generating diversity in Potamogeton. However, the recorded frequency and distribution of hybrids in the world is highly uneven, and so is our knowledge of this diversity. So far, no hybrid between linear-leaved species has been recorded in Turkey. Morphologically intermediate and taxonomically unclear forms collected during an extensive field survey in wetlands throughout Turkey were subjected to detailed morphological and molecular analyses. Direct sequencing and cloning of the ITS region revealed two hybrids previously unknown in Turkey: P. obtusifolius × P. berchtoldii and P. trichoides × P. berchtoldii. Sequences of the chloroplast trnL-trnF intergenic spacer region confirmed P. obtusifolius and P. trichoides as maternal parents of these hybrids. One of the maternal species, P. obtusifolius, is not known to currently occur in Turkey. Brief morphological descriptions of the new hybrids are provided, as well as a comparison of diagnostic characters with those of all parental and similar linear-leaved species. These results demonstrate that hybridization studies and appropriate approaches bring important information about both past and present biodiversity.
