Taxonomic revision of <i>Chlamydomonas</i> subg. <i>Amphichloris</i> (Volvocales, Chlorophyceae), with resurrection of the genus <i>Dangeardinia</i> and descriptions of <i>Ixipapillifera</i> gen. nov. and <i>Rhysamphichloris</i> gen. nov.

<jats:p><jats:italic>Chlamydomonas</jats:italic> (<jats:italic>Cd</jats:italic>.) is one of the largest but most polyphyletic genera of freshwater unicellular green algae. It consists of 400–600 morphological species and requires taxonomic revision. Toward reclassification, each morphologically defined classical subgenus (or subgroup) should be examined using culture strains. <jats:italic>Chlamydomonas</jats:italic> subg. <jats:italic>Amphichloris</jats:italic> is characterized by a central nucleus between two axial pyrenoids, however, the phylogenetic structure of this subgenus has yet to be examined using molecular data. Here, we examined 12 strains including six newly isolated strains, morphologically identified as <jats:italic>Chlamydomonas</jats:italic> subg. <jats:italic>Amphichloris</jats:italic>, using 18S <jats:styled-content style="fixed-case"><jats:italic>r</jats:italic>RNA</jats:styled-content> gene phylogeny, light microscopy, and mitochondria fluorescent microscopy. Molecular phylogenetic analyses revealed three independent lineages of the subgenus, separated from the type species of <jats:italic>Chlamydomonas</jats:italic>,<jats:italic> Cd. reinhardtii</jats:italic>. These three lineages were further distinguished from each other by light and fluorescent microscopy—in particular by the morphology of the papillae, chloroplast surface, stigmata, and mitochondria—and are here assigned to three genera: <jats:italic>Dangeardinia</jats:italic> emend., <jats:italic>Ixipapillifera</jats:italic> gen. nov., and <jats:italic>Rhysamphichloris</jats:italic> gen. nov. Based on the molecular and morphological data, two to three species were recognized in each genus, including one new species, <jats:italic>I. pauromitos</jats:italic>. In addition, <jats:italic>Cd. deasonii</jats:italic>, which was previously assigned to subgroup “<jats:italic>Pleiochloris</jats:italic>,” was included in the genus <jats:italic>Ixipapillifera</jats:italic> as <jats:italic>I. deasonii</jats:italic> comb. nov.</jats:p>