Phylogenetic analysis of the order Nymphaeales based on the nucleotide sequences of the chloroplast ITS2-4 region

The order Nymphaeales is a group of water-living flowering plants. This group is taxonomically small but has great significance in understanding the early evolution of angiosperms. Classification of this order varies from recognition of two to four families. We reconstructed the phylogenetic relationships of six genera of Nymphaeales (Barclaya, Brasenia, Cabomba, Nuphar, Nymphaea, Victoria). The ITS2-4 DNA region of these species was amplified, sequenced and used for phylogenetic analysis. As a result, two clades were resolved: Barclaya + Cabomba and Nuphar + Nymphaea + Victoria. Given that the length of the region analyzed was less than a kilobase, a decision was made to include other genes into the analysis to further verify the results of tree estimations. Thus, we combined ITS2-4 sequences with those of rbcL, matK and 18S rRNA genes. In the latter case, the genera of Nymphaeales form two well-supported clades, however, Barclaya joined the Nymphaea clade. These results support the taxonomic system of Nymphaeales which consists of the two families: Cabombaceae (with the genera Cabomba and Brasenia) and Nymphaeaceae (with the genera Barclaya, Euryale, Nuphar, Nymphaea, Ondinea and Victoria).