Application of Morphological and Molecular Systematics for Identification of Green Microalgae of the Genus Chlorococcum and Some Closely Related Taxa

Polyphyletic nature of three genera of green microalgae, Chlorococcum, Deasonia, and Neospongiococcum, was confirmed. Some Chlorococcum species, together with the type species C. infusionum, formed a true clade Chlorococcum within the macroclade Moewusinia. Its members were characterized by extremely long ITS2 regions with unusual secondary structure. Other species were found to belong to the Stephanosphaerinia macroclade, and should be reclassified accordingly. The research of authentic strains resulted in revised and enhanced morphological descriptions of N. gelatinosum, C. diplobionticum, C. isabeliense, and C.sphacosum. Proposals on taxonomic revision are based on morphological similarity, 18S rRNA distances, presence of compensatory base changes in ITS2 conserved regions, differences in the secondary structure of the spacer, and differences of the helix III conserved motif.