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

Magdalena Anna Dąbrowska,Jan Suda,Polina Volkova,Kaja Rola,Joanna Zalewska-Gałosz

doi:10.5586/asbp.2015.016

Abstract

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.

Highlights

The Nymphaeaceae is a family of hydrophytes that occur in water reservoirs worldwide
This study focuses on four taxa of Nymphaea that belong to the Eurasian Nymphaea clade [3], namely: N. alba L., N. candida J
Our aims were: (i) to identify the sampled specimens based on morphological characters provided in the published determination keys; (ii) to delimit the taxonomic categories based on differences in relative genome size estimated by DNA flow cytometry, (iii) to compare the results of both approaches and discuss potential sources of incongruence, (iv) to assess the frequency of the interspecific hybrid N. ×borealis, based on intermediate genome size values, and (v) to select morphological traits having the greatest discrimination power in morphometric analyses and presenting the highest taxonomic value

Summary

Introduction

The Nymphaeaceae is a family of hydrophytes that occur in water reservoirs worldwide. Nymphaea alba occurs almost throughout Europe with the exception of northern areas and a considerable part of the Iberian Peninsula, and in the Caucasus, western part of Asia and North Africa [5,6,7]. Representatives of N. alba occur in meso- and eutrophic waters, with a pH reaction ranging from weakly acidic to alkaline (pH 5.5–8.3) whereas N. candida prefers poorer, meso- and oligotrophic waters, with a pH ranging from weakly acidic to neutral (pH 5.5–7.1) [9,10]. N. alba often forms phytocoenoses in eutrophic waters and N. candida grows better in more nutrient-poor waters, with a narrower range of requirements [11], ecological requirements of both species overlap and they can be found in both aquatic habitat types [11,12]. Nymphaea tetragona is found in lakes, river backwaters and small oxbow lakes in thickets and silty bottom in the lowland and montane zones [5]

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Conclusion