Modern taxonomic revision of planktic nostocacean cyanobacteria: a short review of genera

The taxonomy of cyanobacteria has been substantially modified in the last few decades, particularly after application of modern ultrastructural and molecular methods. The group of heterocytous cyanobacteria (Nostocales) was found to be monophyletic, but the concept and content of different genera must be continually corrected and revised. The widespread introduction of the molecular approach (especially 16S rRNA gene sequencing) has confirmed almost all traditional genera based on distinct and morphologically recognizable type species, but indicated also broader diversity resulting in separation of more genetic and generic entities in several genera. The combination of molecular and phenotype analyses enables also a better and more objective definition of criteria for describing newly researched generic units, discovered from various habitats in the biosphere. Here, the nostocacean generic taxa are reviewed after recent necessary taxonomic corrections. Nostocacean cyanobacteria are filamentous, heterocytous, not branched and not polarized morphotypes, classified traditionally into one family (Nostocaceae). The main part of the review focuses on the genera containing planktic species.