Genome size and phenotypic variation of Nymphaea (Nymphaeaceae) species from Eastern Europe and temperate Asia

Despite long-term research, the aquatic genus Nymphaea still possesses major taxonomic challenges. High phenotypic plasticity and possible interspecific hybridization often make it impossible to identify individual specimens. The main aim of this study was to assess phenotypic variation in Nymphaea taxa sampled over a wide area of Eastern Europe and temperate Asia. Samples were identified based on species-specific genome sizes and diagnostic morphological characters for each taxon were then selected. A total of 353 specimens from 32 populations in Poland, Russia and Ukraine were studied, with nine biometric traits being examined. Although some specimens morphologically matched N. ×borealis (a hybrid between N. alba and N. candida) according to published determination keys, only one hybrid individual was revealed based on genome size data. Other specimens with intermediate morphology possessed genome size corresponding to N. alba, N. candida or N. tetragona. This indicates that natural hybridization between N. alba and N. candida is not as frequent as previously suggested. Our results also revealed a considerably higher variation in the studied morphological traits (especially the quantitative ones) in N. alba and N. candida than reported in the literature. A determination key for the investigated Nymphaea species is provided, based on taxonomically-informative morphological characters identified in our study