Diversity, taxonomic delimitation, and character evolution of the subfamily Makinoelloideae (Oocystaceae, Trebouxiophyceae, Chlorophyta)

Abstract The subfamily Makinoelloideae (Oocystaceae) comprises a group of small green algae that was established based on molecular phylogenetic data. Members of the subfamily are morphologically diverse, which makes it an excellent group for studies of character evolution. However, there is a dearth of live samples and molecular data for this subfamily because of their rarity. Over the past decade, we have collected and isolated a large number of algal strains from all genera within the subfamily. Based on newly obtained morphological and molecular data, we (1) reconstructed the phylogenetic relationships of the subfamily Makinoelloideae and explored diversity within this group, resulting in the description of a new genus and a new species based on morphology, ultrastructure, and molecular phylogenetic data. The new genus, Campylocystis gen. nov., can be morphologically distinguished from other genera in this subfamily by its solitary curved cells. The new species, Elongatocystis gelatinosa sp. nov., can be distinguished from other members of the genus by its larger cell length and aspect ratio, significantly wider mucilaginous envelope, and fewer number of autospores. In addition, we (2) demonstrated the effectiveness of ITS2/CBCs for taxonomic delimitation of this subfamily. The presence of CBCs and hCBCs can be used to define genera and species, respectively, but they were not positively correlated with taxonomic relationships. Differences in genetic distance among ITS molecular markers can better define intraspecific, interspecific, and intergeneric relationships compared with those among rbcL cpDNA. Lastly, we (3) traced the evolution of six important morphological features in Makinoelloideae and determined their ancestral states, which enhanced our understanding of morphological evolution and species diversity in small green algae.