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ACTA BOTANICA CROATICA
CODEN: ABCRA 25
ISSN 0365-0588
eISSN 1847-8476
ACCEPTED AUTHOR VERSION OF THE MANUSCRIPT
Data on species plasticity and stable characters has an overall importance in
identification keys: comments on Brullo et al. (2022) article
DOI 10.37427/botcro-2023-013
Gábor Sramkó1,2, Attila Takács1,2, Attila Molnár V.1,2, Agnieszka Popiela3, Balázs
András Lukács4
1 University of Debrecen, Department of Botany, Debrecen, Hungary
2 ELKH-DE Conservation Biology Research Group, Debrecen, Hungary
3 University of Szczecin, Institute of Biology, Szczecin, Poland
4 Wetland Ecology Research Group, Centre for Ecological Research, Debrecen, Hungary
Please cite this article as: Sramkó G., Takács A., Molnár V. A., Popiela A., Lukács B.
A.: Data on species plasticity and stable characters has an overall importance in
identification keys: comments on Brullo et al. (2022) article. Acta Botanica Croatica,
DOI: 10.37427/botcro-2023-013.
This is a PDF file of a manuscript that has been accepted for publication. The manuscript will
undergo language and technical editing, formatting and author proofing before it is published
in its final form.
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Commentary
Data on species plasticity and stable characters has an overall importance in identification
keys: comments on Brullo et al. (2022) article
Gábor Sramkó1,2, Attila Takács1,2, Attila Molnár V.1,2*, Agnieszka Popiela3, Balázs András
Lukács4
1 University of Debrecen, Department of Botany, Debrecen, Hungary
2 ELKH-DE Conservation Biology Research Group, Debrecen, Hungary
3 University of Szczecin, Institute of Biology, Szczecin, Poland
4 Wetland Ecology Research Group, Centre for Ecological Research, Debrecen, Hungary
*Corresponding author e-mail: mva@science.unideb.hu
The genus Elatine L. consists of ephemeral species of wetland habitats that live in the
temperate regions of both hemispheres. Their relatively fast life cycle and small habit make
them live an inconspicuous life which was probably the reason behind their relatively little-
studied nature in European botany. Although the botanists of the 19th and early 20th century
discovered all the currently recognised taxa, there were only a few studies that specifically
addressed questions on their biology. This lack of detailed knowledge triggered a more recent
interest in this genus (especially the European members), and several papers provided huge
amount of data and evidence about species ecology, phenotypic plasticity, biogeography,
karyology and molecular taxonomy.
In their recently published paper, Brullo et al. (2022) aimed to lectotypify Elatine
macropoda Guss. and E. gussonei (Sommier) Brullo et al., two enigmatic members of the
genus. They gave an overview of the taxonomic issue of these species, identified the type
specimens, and gave a comprehensive description of both species, as well as aimed to clarify
open questions in the nomenclature of these taxa. However, some of the points raised by Brullo
et al. (2022) are in contrast to previously published scientific evidence, leading them to reach
different taxonomic conclusions. In our view, this contrast is the result of (i) misinterpreted
some key findings published in our works, and (ii) stitching to preconceptions on the
distribution and specific characteristics of these species. Given the importance of scientific
discussion, we here attempt to shed light on contested points to help the better understanding
of the taxonomy of this genus in Europe.
It was interesting to note that Brullo et al. (2022) reported hybridisation to be uncommon
in Elatine, and suggested that it may be a rare phenomenon due to the prevalent autogamous
nature of Elatine species. In their support of this statement, Brullo et al. (2022) cited Razifard
et al. (2017), who reported the allopolyploid hybrid origin of E. americana (Pursh) Arn. and E.
hexandra DC. in their work titled 'Reticulate evolution in Elatine L. (Elatinaceae), a
predominantly autogamous genus of aquatic plants.' We acknowledge the reference made by
Brullo et al. (2022) to Razifard et al. (2017) as an example of hybridisation in Elatine species.
Furthermore, our own results demonstrated the presence of hybrid lineages in Elatine section
Elatinella subsection Macropodae, which includes the focal species of Brullo et al.'s (2022)
work. Given our findings, along with the previous reports by Sramkó et al. (2016) and Takács
et al. (2017), which were also cited by Brullo et al. (2022), it is possible that hybridisation in
this genus may be more common than accepted. While the authors may have been aware of the
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presence of hybridisation in their focal group, we appreciate their analysis and interpretation of
the available data, but we must disagree with them: hybridisation is not so rare in this genus.
In light of this, it is not appropriate to consider as a “surprising consequence” that two
species of Elatine live in sympatry on the island of Sicily, because hybridisation – that does not
seem as rare as suggested by Brullo et al. (2022) – requires the close encounter of different
species at least some point during their evolutionary history. What would have been more
important in this respect is to make a reference to the admixed lineage made up of E. gussonei
from Lampedusa and Malta (Sramkó et al. 2016, Takács et al. 2017). The introgressed nature
of these samples may explain some morphological differences of these populations from the
rest of the distribution area of E. gussonei, which may be behind the view of seeing these
populations as “different” by various scholars. In this respect it is noteworthy to refer to the
unfortunate use of a Lampedusa plant without characterising its nuclear genome as the lectotype
of E. gussonei now selected by Brullo et al. (2022) can also be an introgressed plant.
Besides hybridisation, our detailed study (Molnár et al. 2015) of the well-known
phenotypic plasticity of vegetative characters in this amphibious genus (Mason 1956, Mifsud
2006) is another key piece in the literature that is generously overlooked by Brullo et al. (2022).
Although they refer to the existence of phenotypic plasticity, in this context they failed to cite
the results of Molnár et al. (2015) on the stability of seed characteristics and instability of
vegetative and floral characters. This explains why they refer to the length of the petal and the
sepal as one of the key characters separating the species E. macropoda and E. gussonei.
Although Gussone (1827), Sommier (1907) and Pignatti (2017) emphasised the relevance of
floral characters in the taxonomy of Elatine, we must take to account that Mifsud (2006) has
already documented the instability of these characters, which is simply rejected by Brullo et al.
(2022) on the basis of a subjective evaluation (“In our opinion, the floral traits cannot be linked
exclusively to environmental conditions or flowers age”) and claim the opposite, citing their
observations without measured and tested dataset (“based on our observations, E. gussonei
(Lampedusa and Malta) is morphologically distinct from the typical E. macropoda”). Sommier
(1907) has already emphasized that E. gussonei differs from E. maropoda by its more curved
seeds. In line with Sommier’s and Mifsud’s work, our measured dataset and statistical analyses
demonstrate that seed morphology, especially its shape and surface ornamentation remains
stable under different environmental conditions (Molnár et al. 2015), hence these are the most
obvious morphological characters to differentiate species of Elatine, at least on the studied area.
Moreover, this study also showed that the amount of light alone has a significant effect on the
morphology of the vegetative and floral parts of the plants. Compared to plants growing under
natural light conditions, internodes, pedicels, caulin- and sepal leaves are longer of in vitro
grown individuals exposed to less intense artificial light (Fig. 1. A, B).
Brullo et al. (2022) was selective in its choice when accept the taxonomic importance of
seed “ornamentation” (i.e., the shape of epidermal pits on the surface of the seed), but denies
the utility of seed curvature, although our results (Molnár et al. 2015) clearly demonstrated the
taxonomic value of this character (Fig. 2). It may be noted here that our very recently published
paper (Łysko et al. 2022) emphasises this role even more: we tested several analytical methods
on the discriminatory power of seed morphometry in the genus, where seed shape and
ornamentation were found as highly discriminatory. But regardless of this new result, Brullo et
al. (2022) falsely refer to Sramkó et al. (2016) as the source of information on seed morphology
being “quite variable trait even within the single populations” because that study summarised
seed morphology of different populations at the species-level (given the main aim of
reconstructing the evolutionary history of the genus).
In order to demonstrate the usefulness of the preferred seed morphological characters,
Brullo et al. (2022) published scanning electron microscope (SEM) images of seeds of E.
macropoda (Brullo et al. 2022: Fig. 4) and E. gussonei (Brullo et al. 2022: Fig. 6), plus a
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comparative close-up image on epidermal pit shape of both species (Brullo et al. 2022: Fig. 5)
where we can see pits of “rectangular or slightly hexagonal” shape as typical of E. macropoda
(Brullo et al. 2022: Fig. 5A), and pits of “more or less isodiametric and usually hexagonal”
shape as typical of E. gussonei (Brullo et al. 2022: Fig. 5B). Although the authors do not provide
us with any measurement data for a statistically sound comparison, the visual inspection of their
Fig. 4 would leave most observer with the impression that Fig. 4C and Fig. 4D (Sicilian plants
from Modica and Ispica, respectively) are more similar to Fig. 5B, therefore, should be
identified according to their epidermal seed pit shapes as E. gussonei.
In fact, both the seed curvature and epidermal structure clearly suggest the correct
identification of the plants shown from Modica and Ispica as E. gussonei. Although Brullo et
al. (2022) argue for the importance of longer petal length as a distinctive character that defines
E. gussonei, it is rather easy to find Elatine plants with short petals on the island of Malta (see
Fig. 1 B) where – according to Brullo et al. (2022) – only E. gussonei lives. Such plants were
also presented by Mifsud (2006) and further examples can be seen in his photographic
collection (https://maltawildplants.com/ELTN/Elatine_gussonei.php). If Brullo et al. (2022)
were to consider the role of seed morphological characters in the genus and take into account
the numerous publications that discuss the plastic nature of vegetative and floral characters
(Molnár et al. 2014, 2015, Sramkó et al. 2016, Takács et al. 2017, Łysko et al. 2022) as well as
the phylogenetic results (Sramkó et al. 2016, Razifard et al. 2017) in greater detail, they may
find it easier to accept the presence of E. gussonei in Sicily and other Mediterranean areas. We
must note here it is common in taxonomy for researchers to rely on different sets of characters
and hold differing taxonomic opinions.
We accept, however, that this contradicts the well-established view on the very limited
distribution and endemic nature of E. gussonei (Brullo et al. 1998, 2022), and would also
necessitate the conservation re-evaluation of this species (Takács et al. 2017). Having said that
we also think this species will still remain one of the key characteristic species of temporary
Mediterranean ponds that – quite correctly! – enjoy the highest level of conservation interest in
the European Union. Therefore, the taxonomic re-interpretation of E. gussonei and the
consequently larger distribution area (that is still a Mediterranean endemic!) is not a concern
for this plant from a conservation point of view. Instead, a better understanding of taxonomy is
a fundamental prerequisite of well-established species conservation (Mace 2004).
In summary, Brullo et al. (2022) downplay i) the importance of seed shape as an
identification character and ii) the environment (primarily light intensity) and phenology
depending nature of floral characters. While their results are based on seed pit morphology,
which lacks report of detailed statistical analyses, it is important to note that these values can
be compared and verified. However, it is necessary to maintain scientific rigor, and the lack of
detailed measurements and rigorous statistics in their report may limit the ability to verify the
findings. Regarding to the contradictions among our previously presented coherent works and
recent claims of Brullo et al. (2022), we cannot accept their statements on the morphology and
distribution of Elatine macropoda and E. gussonei. We further claim that their identification
key for European (and not Mediterranean, as they indicated) Elatine species is misleading, since
focuses on phenotypically plastic characters thus we recommend using the key presented in
Popiela et al. (2017) to identify European species of Elatine.
References
Brullo, S., Brullo, C., Tavilla, G., Cambria, S., Minissale, P., Sciandrello, S., Giusso del Galdo,
G., Siracusa, G., Del Guacchio, E., 2022: About the occurrence of Elatine macropoda
and E. gussonei (Elatinaceae) in Sicily and lectotypification of their names. Acta Botanica
Croatica 81, 129–139. https://doi.org/10.37427/botcro-2022-010
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Gussone G., 1827: Florae Siculae prodromus, vol. 1. Ex Regia Typographia, Neapoli.
Łysko, A., Popiela, A., Forczmański, P., Molnár, V.A., Lukács, B.A., Barta, Z., Maćków, W.,
Wolski, G.J., 2022: Comparison of discriminant methods and deep learning analysis in
plant taxonomy: a case study of Elatine. Scientific Reports 12, 20450.
https://doi.org/10.1038/s41598-022-24660-1
Mace, G.M., 2004: The role of taxonomy in species conservation. Philosophical Transactions
of the Royal Society 359, 711–719. https://doi.org/10.1098/rstb.2003.1454
Mifsud, S., 2006: A comparative study between Elatine gussonei (from Malta) and Elatine
macropoda (from Majorca). Aquatic Gardeners. Retrieved December 5, 2022 from
http://www.aquatic-gardeners.org/elatine/Comparitive_study.pdf
Molnár, V.A., Popiela, A., Lukács, B.A., 2014: Elatine gussonei (Sommier) Brullo et al.
(Elatinaceae) in Sicily. Plant Biosystems 148, 27–30.
https://doi.org/10.1080/11263504.2013.788099
Molnár, V.A., Tóth, J.P., Sramkó, G., Horváth, O., Popiela, A., Mesterházy, A., Lukács, B.A.,
2015: Flood induced phenotypic plasticity in amphibious genus Elatine (Elatinaceae).
PeerJ 3: e1473. https://doi.org/10.7717/peerj.1473
Pignatti, S., 2017: Elatine L. In: Pignatti, S. (ed.), Flora d’Italia, vol. 2, 313–315. Edagricole,
Milano.
Popiela, A., Łysko, A., Białecka, B., Bihun, M.M., Sramko, G., Staroń, W., Wieczorek, A.,
Molnár, A., 2017: Seed morphometric characteristics of European species of Elatine
(Elatinaceae). PeerJ 5: e3399. https://doi.org/10.7717/peerj.3399
Razifard, H., Les, D.H., Tucker, G.C., 2017: Reticulate evolution in Elatine L. (Elatinaceae), a
predominantly autogamous genus of aquatic plants. Systematic Botany 42, 87–95.
https://doi.org/10.1600/036364417X694610
Sommier, S., 1907: Flora delle Isole Pelagiche. Bollettino del Reale Orto Botanico di Palermo
5 (1906). Appendix 76 (-78)
Sramkó, G., Molnár, V.A., Tóth, J.P., Laczkó, L., Kalinka, A., Horváth, O., Skuza, L., Lukács,
B.A., Popiela, A. 2016. Molecular phylogenetics, seed morphometrics, chromosome
number evolution and systematics of European Elatine L. (Elatinaceae) species. PeerJ
4:e2800. https://doi.org/10.7717/peerj.2800
Takács, A., Molnár, V.A., Horváth, O., Sramkó, G., Popiela, A., Mesterházy, A., Lovas-Kiss,
Á., Green, A.J., Löki, V., Nagy, T., Lukács, B.A., 2017: The rare aquatic angiosperm
Elatine gussonei (Elatinaceae) is more widely distributed than previously thought.
Aquatic Botany 141, 47–50. https://doi.org/10.7717/peerj.4913
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Fig. 1. Flowering specimens of Elatine gussonei: A – cultivated (in vitro) from Lampedusa, B
– indigenous (in situ) from Malta. Petal/sepal ratio is occasionally <1. According to Brullo et
al. (2022) erroneous assumption this is a distinguishing character that is specific to E.
macropoda (see Brullo et al. 2022, Fig. 2). (Photo: B.A. Lukács).
Fig. 2. Comparison of seeds of Elatine gussonei and E. macropoda. Scale bars = 0.1 mm. (SEM
photo: A. Popiela).
