Reticulocystis yunnanense gen. et sp. nov., a new member of freshwater Oocystaceae algae (Trebouxiophyceae, Chlorophyta)

Oocystis-like algae are diverse and found throughout the world. In this study, two new strains of algae with colonies resembling Oocystis were identified and successfully cultured in the laboratory. A polyphasic approach, including light microscopy, transmission electron microscopy and phylogenetic analyses of 18S rDNA and rbcL cpDNA, was used to characterize the strains. Observation of the two strains showed a regular colonial morphology (cells/daughter colony are parallel to each other and positioned near the edge of the mother cell wall) and a characteristic fibrillar network structure on the mother cell wall is obvious in light microscopy, which distinguished them from other Oocystis-like members described previously. Molecular analyses revealed that the two strains form an independent lineage within the subfamily Makinoelloideae (Oocystaceae, Trebouxiophyceae), separated from other genera. Therefore, we described this alga as Reticulocystis yunnanensis gen. et sp. nov. The genera of Makinoelloideae with similar colonial morphotypes were revealed as not monophyletic and the relationships between them remained undetermined. Additional taxon sampling and data from additional multiple genes are necessary to assess the taxonomy of the Makinoelloideae.