Morphology, ecology, and 18S rDNA phylogeny of the green microalgal order Protosiphonales (Chlorophyceae, Chlorophyta)

The system of the green microalgal order Protosiphonales (Chlorophyceae, Chlorophyta) constructed based on morphological, ecological, and molecular genetic data is considered. Subdivision of the order (=macroclade Stephanosphaerinia) into four groups is proposed, with three probably corresponding to the families Stephanosphaeraceae, Chlorococcaceae, and Protosiphonaceae and the fourth having an indefinite status. The diagnostic characteristics of the families, genera, and species are discussed, as well as the independent rank of some taxa. Morphological descriptions of a number of species are supplemented. Based on polyphasic approach, strain ACSSI 23 is proposed as a candidate for a new genus and species.