Sheathia yunnanensis, a new species of freshwater red alga (Rhodophyta: Batrachospermales) from Yunnan, China

The freshwater red algal genus Sheathia is one of the most species-rich genera in the Batrachospermales, containing species with heterocortication (both bulbous and cylindrical cells covering the main axis) and homocortication (only cylindrical cells). The hidden diversity of homocorticated Sheathia species has gained research momentum. Recent studies have revised these taxa and described many new species. In this study, a new homocorticated Sheathia species is described and illustrated from Yunnan, China, based on phylogenetic analyses of DNA sequence data. Sheathia yunnanensis sp. nov is morphologically characterized by having homocortication, carpogonium with bent or slightly constricted lanceolate trichogyne, large carposporophyte and carposporangium. However, it is only distinguishable from other homocorticated species by DNA sequence data. Phylogenetic analyses based on rbcL, COI-5P, psbA and concatenated rbcL + COI-5P alignment indicated that Sheathia yunnanensis form an independent clade from other homocorticated Sheathia species with high interspecific divergence (rbcL: 3.9-4.9%/37-54 bp, COI-5P: 6.1-6.6%/36-39 bp and psbA: 2.2-3.9%/18-32 bp). Sheathia yunnanensis, as the first gametophyte of Sheathia species reported in Yunnan, differs from other Sheathia species reported only as 'Chantransia' sporophyte stage. As a result of this study, the number of Sheathia species recognized in China increased to eight, including one heterocorticate and seven homocorticated including three only known from the 'Chantransia' sporophyte stage. The description of this new species expands the diversity of Sheathia in the world.