Abstract
Chlorellacean members are common in aquatic or subaerial habitats, and many of them have significant economic value. Taxonomic reports and organelle genome data for the Nannochloris clade, an important subgroup within this family, are limited, hindering the understanding and exploitation of this clade. In this study, a fusiform-celled strain, FACHB-3607, was isolated from a pond in China. Through examination of morphological characteristics and phylogenetic analyses of rbcL, 18S rDNA, and ITS, it was identified as a new species within the Nannochloris clade, named Koliella bifissiva sp. nov. In addition, this study provided a first insight into the organellar genomes of the genus Koliella. The K. bifissiva chloroplast had a 99.8 kb genome, and the mitochondrion had a 40.8 kb genome, which are moderate sizes within the Nannochloris clade. Phylogenomic analysis showed that K. bifissiva is most closely related to Nannochloris sp. "desiccata", followed by Marvania. In contrast, Picochlorum was the most distantly related species. The organelle genomes of the Nannochloris clade display dynamic evolution, reflected in variations in genome size, gene content and order, and selection pressure. This research enhances our knowledge of species diversity and evolutionary history in the Nannochloris clade.