Freshwater "microcroissants" shed light on a novel higher-level clade within Trebouxiophyceae and reveal the genus Chlorolobion as a trebouxiophyte

Abstract

Trebouxiophyceae is a widespread and species-rich green algal class encompassing mostly coccoid algae with a simple ovoid or ellipsoidal outline. However, some poorly-sampled lineages have evolved more elaborate shapes or even complex thalli, adding to the classs morphological diversity. Led by new and previously established strains, this study additionally uncovered a clade of croissant-like trebouxiophytes. Phylogenetic analyses inferred from nuclear 18S rDNA and chloroplast rbcL sequences confirmed the monophyly of the microcroissant clade, which we propose to be classified as a new family, Ragelichloridaceae. This family includes two novel genera, Ragelichloris and Navichloris, and the previously described Thorsmoerkia. The position of Ragelichloridaceae within Trebouxiophyceae stayed unresolved but chloroplast phylogenomics showed that the family belongs to the broader incertae sedis group, which also includes Xylochloris and Leptosira. In addition, our study showed that the microcroissant-like genus Chlorolobion, previously classified within Chlorophyceae, is a genuine trebouxiophyte, potentially related to Ragelichloridaceae. HighlightsO_LIA new family-level clade uncovered within Trebouxiophyceae. C_LIO_LITwo new genera described. C_LIO_LIThe genus Chlorolobion shown to be a trebouxiophyte. C_LI