Intraspecific differentiation of Sparganium erectum in the Czech Republic: molecular, genome size and morphometric analysis

Aquatic and wetland plants tend to be very phenotypically plastic, which accounts for the taxonomic difficulties in many groups. In the genus Sparganium, which comprises about 14 species, numerous taxa at different ranks are described. The classification of the genus is based on generative characters on the fruit, which are less influenced by the environment than vegetative characters. Nevertheless, the intraspecific division of Sparganium erectum poses problems, especially the existence of several intraspecific taxa along with intermediate individuals. In this study we examined four European subspecies of S. erectum (subsp. erectum, subsp. microcarpum, subsp. neglectum and subsp. oocarpum) from 64 populations in the Czech Republic. A combination of multivariate morphometrics, AFLPs and genome size estimation allowed us to confirm the current subspecies classification and investigate putative intraspecific hybridization. Four genetic groups with different genome sizes corresponding to the subspecies were found. Morphological characters that were described in previous studies correlated with these genetic groups and thus affirmed the classification. The most important characters for subspecies differentiation were width and length of fruit, style length, length of the upper part of the fruit and constriction in the middle part of the fruit. In addition, admixed individuals between the genetic groups were recorded. The hybrid origin of subsp. oocarpum was confirmed, being derived from the crossing of subsp. erectum and subsp. neglectum. Finally, three other hybrid combinations were detected, suggesting recent hybridization: subsp. erectum × subsp. microcarpum, subsp. microcarpum × subsp. neglectum, and subsp. erectum × subsp. oocarpum.