ABSTRACT Despite significant recent advances, our understanding of the diversity and phylogeny of coccoid green algae remains incomplete, partly because of the existence of numerous previously described taxa that are yet to be reinvestigated to clarify their identity and phylogenetic position. An essentially forgotten taxon is the genus Coleochlamys Korshikov, presently classified in the class Chlorophyceae. Here we present the results of our investigations of one new and four previously available strains identified as Coleochlamys. Based on morphological features and molecular evidence, the strains represented two clearly differentiated species: Co. apoda, the type species of the genus, and Co. oleifera, which are both epitypified in this study. The two species differ in cell shape and presence or absence of a cell wall extension resembling a papilla. They are also differentiated by multiple compensatory base changes (CBCs) in the ITS2 region. Our data support the previous proposal that the genera Rhopalocystis and Fusochloris are later synonyms of Coleochlamys, and additionally suggest that the algae originally described as Characium perforatum K.W. Lee & H.C. Bold and Rhopalocystis cucumis are conspecific with Co. apoda. Phylogenies of both 18S rRNA and rbcL genes place Coleochlamys in the class Trebouxiophyceae, in a clade with Microthamnion. Analysis of environmental DNA data has revealed the existence of at least one additional Coleochlamys species, and of a closely related sister lineage (potentially a separate genus) encountered in an Alaskan glacier. The occurrence data on Coleochlamys indicate that the genus includes psychrotolerant algae that may be common in cold environments worldwide.