Chloroplast Genome and Description of sp. nov. (Chlamydomonadales, Chlorophyta), a Rare Aerial Alga from China.

The genus is extremely rare and is the subject of limited research and reports. It currently comprises only two species, and , which differ from other globose algae due to their unique centrally radiating chloroplasts. In this study, we describe a new specimen in detail based on morphological data and phylogenetic analysis and identify it as . and exhibit a high degree of similarity, likely due to their shared characteristics of centrally radiating chloroplasts and flagella that are significantly longer than the cell body. A phylogenetic tree constructed based on the 18S rDNA sequence indicates that and form a branch that is distinct from other genera, such as , , and . Phylogenetic analysis of the ITS sequence, the L gene, and the A gene reveals that is significantly different from , in that it has oil droplets, smaller vegetative cells and zoospores, and distinct habitats. It is also different from as it has smaller vegetative cells and zoospores, turns red after cultivation, has longer flagella, and resides in different habitats. The chloroplast genomes of and further show significant differences, with the phylogenetic tree constructed based on the analysis of 49 protein-coding genes forming two separate branches. The collinearity of the chloroplast genomes in and is poor, with 15 out of the 31 homologous modules displaying inversions and complex rearrangements. Given these differences, we classify this alga as a new species and named it sp. nov.