We investigated the phylogenetic relationships and the taxonomy of 20 sarcinoid strains by their morphological features and using 18S rDNA sequence data. Nineteen strains of Chlorosarcinopsis (Gerneck) Herndon and allied genera were divided into four groups (A–D). Group A, comprising eight species, was concordant with the description of Chlorosarcinopsis and divided into four polyphyletic subgroups. Group B included two species of Chlorosarcinopsis and two strains of Desmotetra stigmatica (Deason) Deason et Floyd, all of which had parallel thylakoid membranes in pyrenoid matrices, and zoospores bearing apical stigma and subapical flagellar apparatus. The definition of Desmotetra Deason et Floyd was emended to include these features, and Chlorosarcinopsis delicata S. Watanabe was transferred to this genus. Group C comprised Chlorosarcina stigmatica Deason (ASIB.T105), for which we proposed Sarcinochlamys gen. nov., a genus distinct from Chlorosarcina Gerneck in having walled zoospores. Group D, comprising six species, corresponded to Neochlorosarcina and was divided into two subgroups. The presence of thin cell walls in Neochlorosarcina S. Watanabe was ascertained as a valid feature for circumscribing the sarcinoid genera. The physiological experiments on the species of Chlorosarcinopsis and Chlorosarcina by Groover and Bold (1968) were assessed based on the phylogenetic results. Groups (A, B, D) were roughly characterized by these features: algal mass color, utilization of selected nitrogen compounds and carbon sources under light/dark and aerobic/anaerobic conditions, and requirement for vitamin B12. Molecular analysis revealed that Chlorosphaeropsis alveolata Herndon had closer affinity with solitary Protosiphon Klebs and Spongiochloris Starr than with sarcinoid members.