Reevaluation and discovery of new species of the rare genus Watanabea and establishment of Massjukichlorella gen. nov. (Trebouxiophyceae, Chlorophyta) using an integrative approach.

Chlorella-like coccoid green algae are widely distributed in almost all terrestrial habitats and belong to different lineages of the Chlorophyceae and Trebouxiophyceae. The Watanabea clade of the Trebouxiophyceae shows a high genetic biodiversity. Re-investigation of the authentic strain of the rarely found W. reniformis showed several morphological differences compared to the original description. To clarify the taxonomic status of Watanabea, we compared several new isolates with similar morphology. Phylogenetic analyses of the SSU and SSU+ITS rDNA sequences revealed that all new isolates were distinct from W. reniformis. The ITS-2/CBC approach clearly demonstrated that the strains belonging to Watanabea represented species. We emended the generic diagnosis of Watanabea, and proposed four new species. One strain, SAG 2552, represented a separate lineage that we propose as a new genus Massjukichlorella with one species M. epiphytica.