Finding <i>Euastropsis</i> Lagerheim (Chlorophyceae): Insights into morphological and genome evolution in the green algal family Hydrodictyaceae

Recent phylogenetic studies of the family Hydrodictyaceae (Sphaeropleales, Chlorophyceae) included all but one of the genera, Euastropsis, which was excluded due to a lack of living material. A 2017 discovery of E. richteri in Lake Kocie, Poland, provided an opportunity to study the morphology, ultrastructure, plastome architecture, and phylogenetic placement of this monotypic genus. The overall morphology fit the original description, being two-celled with some variations in size and number of daughter coenobia. The plastome (GenBank accession PQ469705) architecture and gene content of E. richteri are characteristic of Hydrodictyaceae. Phylogenetic analyses placed E. richteri as a sister lineage to morphologically similar Stauridium tetras. These new data add to our understanding of evolutionary trends in the Hydrodictyaceae, whose members exhibit specific colonial morphology varying in size, shape, and complexity.