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

Abstract

Chlamydomonas (Cd.) 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. Chlamydomonas subg. Amphichloris 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 Chlamydomonas subg. Amphichloris, using 18S rRNA gene phylogeny, light microscopy, and mitochondria fluorescent microscopy. Molecular phylogenetic analyses revealed three independent lineages of the subgenus, separated from the type species of Chlamydomonas, Cd. reinhardtii. 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: Dangeardinia emend., Ixipapillifera gen. nov., and Rhysamphichloris gen. nov. Based on the molecular and morphological data, two to three species were recognized in each genus, including one new species, I. pauromitos. In addition, Cd. deasonii, which was previously assigned to subgroup "Pleiochloris," was included in the genus Ixipapillifera as I. deasonii comb. nov.

Chloromonas svalbardensis n. sp. with Insights into the Phylogroup Chloromonadinia (Chlorophyceae)

“…However, while 18S rRNA gene sequence analyses place Ixipapillifera as a sister lineage to Chloromonas clade 2 (Nakada et al. ), our study does not show statistical support. In contrast, the multigene phylogenetic analyses of Chloromonadinia placed Ixipapillifera as a sister lineage to clade 3 (Matsuzaki et al.…”

“…Our phylogenetic trees along with a number of previous studies (Nakada et al. , ; Remias et al. ) demonstrate that Chloromonas is paraphyletic and that the genus should be split into a number of smaller entities.…”

“…In addition, a new genus Ixipapillifera Nakada was recently proposed within Chloromonadinia based on a combination of molecular and morphological data (Nakada et al. ). Therefore, the current phylogenetic status of the phylogroup is not clear, especially the monophyly of the genus Chloromonas .…”

Molecular phylogeny, systematics, and revision of the type species of Lobomonas, L. francei (Volvocales, Chlorophyta) and closely related taxa

“…This already was shown in the phylogenetic tree based on 18S rDNA presented by Nakada et al. () and is confirmed here. The sister group relationship of this taxon with Vitreochlamys fluviatilis (strain NIES‐879), the generitype species, deserves further scrutiny.…”

“…, Nakada et al. ) and thus the phylogenetic position of Lobomonas within the Volvocales is uncertain.…”