Two new Dictyosphaerium-morphotype lineages of the Chlorellaceae (Trebouxiophyceae): Heynigia gen. nov. and Hindakia gen. nov.

Previous studies on the colonial coccoid green algal genus Dictyosphaerium have shown a polyphyletic origin of this morphotype within the Chlorellaceae. Recent molecular analyses assigned the type species D. ehrenbergianum to the Parachlorella clade of the Chlorellaceae. In the present study we focused on strains of D. tetrachotomum, one of the most frequent morphospecies of the genus in inland waters. Analyses of combined SSU and ITS rRNA gene sequences revealed that strains with D. tetrachotomum morphology do not share a close phylogenetic relationship with the type species D. ehrenbergianum. These strains are part of a subclade of the Chlorella clade of the Chlorellaceae, nested between members of Didymogenes and a second new lineage of different Dictyosphaerium-like strains. Due to the unique position of these strains in the tree, we here establish the new genera Hindakia and Heynigia. Morphological analysis and phylogenetic and secondary structure analyses of the SSU, ITS1 and ITS2 of Hindakia strains have revealed considerable differences within this subclade, leading to the separation of two distinct species: H. tetrachotoma and H. fallax. Closely related to this new genus are two colony-forming strains with spherical cells, constituting a distinct lineage consisting of Heynigia dictyosphaerioides, sp. nov., and Heynigia riparia, sp. nov. Further, our results have confirmed the polyphyletic origin of the Dictyosphaerium morphotype within the Chlorellaceae.