Phylogenetic relationships among seven freshwater red algal genera in the Batrachospermaceae (Batrachospermales, Rhodophyta) using complete chloroplast genome data

Systematics studies within the freshwater red algal order Batrachospermales have used only one to a few genes to infer evolutionary relationships. The phylogenetic trees presented in these studies recovered monophyletic genera with strong support, but the relationships among genera were often not well supported. Chloroplast genome sequencing may provide the necessary data to obtain a fully resolved, strongly supported phylogeny. In order to test the efficacy of this approach, we focused on a subclade of seven genera and sequenced chloroplast genomes from 10 species. Utilizing new and previously published data, a phylogeny was constructed from 132 chloroplast-encoded genes. The relationships among all seven genera had strong statistical support. The phylogeny and gross morphology of genera showed concordance. Lemanea and Paralemanea with tube-like pseudoparenchymatous gametophytes formed a clade, and five genera-Batrachospermum, Lympha, Sirodotia, Tuomeya, and Volatus-with beaded gametophytes formed a second clade. Within the clade of five genera, Batrachospermum with pedicellate carposporophytes was sister to the other three genera with axial carposporophytes and Sirodotia with prostrate carposporophytes along the axis. The results highlight the potential for chloroplast genome data to clarify evolutionary relationships in the Batrachospermales, offering a promising approach for future studies aimed at understanding the broader evolutionary history of this group.