Generic and species concepts in Microglena (previously the Chlamydomonas monadina group) revised using an integrative approach

Traditionally the genus Microglena Ehrenberg has been used to contain species that belong to the Chrysophyceae; however, the type species of Microglena, M. monadina, represents a green alga, which was later transferred to the genus Chlamydomonas. The taxonomic status of the genus has therefore remained unclear. We investigated 15 strains previously assigned to C. monadina and two marine species (C. reginae and C. uva-maris) using an integrative approach. Phylogenetic analyses of SSU and ITS rDNA sequences revealed that all strains form a monophyletic lineage within the Chlorophyceae containing species from different habitats. The strains studied showed similar morphology with respect to cell shape and size, but showed differences in chloroplast and pyrenoid structures. Some representatives of this group have the same type of sexual reproduction (homothallic advanced anisogamy). Three different morphotypes could be recognized. Strains belonging to type I have a cup-shaped chloroplast with a massive basal part, in which a large, single, ellipsoidal pyrenoid is located. The members of type II also have a cup-shaped chloroplast, which is partly lobed and has a thinner basal part than type I; here the pyrenoid is half-ring or horseshoe-shaped and occupies different positions in the chloroplast depending on the strain. The strains of type III have multiple pyrenoids, which appear to have developed from the subdivision of a single ring-shaped pyrenoid into several parts. We compared the results of our morphological investigations with the literature and found that 15 strains could be identified with existing species. Two strains did not fit with any described species. As a result of our study, we transfer all strains to the genus Microglena, propose 11 new combinations, and describe two new species. Comparison of the ITS-1 and ITS-2 secondary structures confirmed the species delineations. All species have characteristic compensatory base changes in their ITS secondary structures and are supported by ITS-2 DNA barcodes.