Climate-dependent distribution of Lemna minor, L. turionifera and L. × japonica (Lemnaceae) in temperate Eurasia and high variability of their genome size

In spite of a burst of duckweed biology studies, understanding their diversity is still in progress. We examined 174 reliably-identified (intron length polymorphism in TUBB1) samples of the Lemna minor complex from East Europe and North Asia (41 localities of L. minor, 58 localities of L. turionifera, and 75 localities of their hybrid, L. × japonica) and described clear patterns of their distribution. It is mainly determined by climatic preferences (i.e., the ability to survive unfavorable conditions). Namely, the ranges of L. minor and L. turionifera in the lowlands are separated by the Urals, with populations located west and east of these mountains respectively and coinciding with an eastward increase of climate continentality. However, historical (i.e. European origin of the species) and not ecological factors should explain the absence of L. minor in rather mild climate of the southern Russian Far East. The hybrid has an intermediate ability to tolerate continental climate, and co-occurs with one of its parents. In southern mountains (the Caucasus and Tian-Shan) the three taxa are separated by local climate conditions, determined by the terrain. We revealed high continuous variability of genome sizes within each taxon (two-fold in L. minor and L. turionifera; three-fold in L. × japonica), which is not explained by environmental factors. We propose an approach for distinguishing these three taxa in temperate Eurasia using morphology. We have not documented the invasive spread of L. aequinoctialis, L. minuta and L. turionifera in East Europe.