Molecular phylogeny and character evolution of family Selenastraceae (Sphaeropelales, Chlorophyceae, Chlorophyta)

The family Selenastraceae comprises a group of very common small green algae which have extensive application value across various economic sectors. However, the taxonomic status of the family is highly confused, and the phylogenetic relationships among the major taxa within the family remain unclear. In this study, we obtained 90 new algal strains from across China, identified 24 species and a large number of undetermined species, and added 167 new molecular sequences, significantly expanding the data volume for this family. The phylogenetic positions of genus Apodococcus and eight species were determined for the first time. Based on more reliable phylogenetic relationships, we systematically organized and discussed the existing and newly discovered polyphyly issues of the genera Ankistrodesmus, Monoraphidium, Kirchneriella, Raphidocelis and Nephrochlamys. We also proposed that the genus Ankistrodesmus may represent an early-evolving lineage within the family. Furthermore, ancestral reconstruction analysis indicated that fusiform cell shape, unicellular or small-colony, parallel arrangement of autospores, release of autospores via median split of mother cell wall, naked pyrenoids, and a thin mucilaginous envelope were plesiomorphies within the family. In the future, the acquisition of additional algal strains and molecular data will help to construct more stable phylogenetic relationship among taxa and further complete the taxonomic revision of the family Selenastraceae.