Morphology, phylogeny, and organelle genomics of three new Rhopalodia species (Rhopalodiales, Bacillariophyceae)

Three new species of the freshwater diatom genus Rhopalodia from Yunnan province, China, have been described in this study based on a combination of morphological and molecular data. The diagnostic characteristics of Rhopalodia yunnanensis sp. nov. are the absence of secondary costae, and spines on its outer surface exhibit a flame-like morphology. Rhopalodia inflata sp. nov. is distinguished from other Rhopalodia species by the pronounced dorsal middle inflation, blunt-pointed spines, and areolae occluded by volae that consist of two or three c-shaped openings. The areolae of R. fuxianensis sp. nov. are covered by raised siliceous petal-like occlusions with one to two siliceous processes. Phylogenetic analysis based on the SSU rDNA and rbcL sequence data places the three new species within a distinct clade, clearly separated from other sequenced Rhopalodia species, including the generitype, R. gibba. In addition, the plastid, mitochondrial, and spheroid body genomes of the three novel species are presented and characterized in this paper.