Phylogenetic relationships in the genus Closterium

Desmids are a large polyphyletic group of streptophyte algae, numbering about 4000 species. Traditionally, the taxonomy of desmids is based on morphological characters. However, the latest molecular genetic studies of the group conflict with the established taxonomy and indicate the polyphyletic position of some genera of this group of algae. The genus Closterium Nitzsch ex Ralfs, like the family Closteriaceae Bessey, forms a monophyletic clade on the general tree of Desmidiales, recovered on the data of both 18S rDNA and rbcL cpDNA. In our analysis of phylogenetic relationships within the genus Closterium, the existing strains formed 14 clades (species complexes). Within some complexes, some strains don’t differ phenotypically, but diverge on the phylogenetic tree, which indicates a hidden taxonomic diversity within the genus.