Diversity and revised classification of Polysiphonia sensu lato from the San Juan Islands based on morphology and molecular evidence

Abstract

The large red algal group Polysiphonia sensu lato dominantly represents the Streblocladieae and Polysiphonieae tribes. The segregation of 12 genera under the Streblocladieae tribes further suggests the taxonomic update of this group. Specimens believed to be Polysiphonia were collected during low tide for this study at different locations throughout San Juan and Lopez Island and processed at Friday Harbor Laboratory (FHL) in June 2023. Initially, the fresh specimens were separated under a dissecting scope, selected for DNA extraction, and representative specimens were pressed between the herbarium sheets. The branching patterns, presence or absence of trichoblast cells, rhizoidal attachment, number of pericentral cells, and reproductive features were considered for anatomical study. A total of 36 specimens were sequenced, amplifying the rbcL gene, and sequenced data were aligned with worldwide representative species, and maximum likelihood (ML) was performed for the phylogenetic analysis. Our results revealed six species belonging to four genera. Four species, namely: Eutrichosiphonia confusa (Hollenberg) Savoie & G.W. Saunders; Polysiphonia determinata Hollenberg; Vertebrata hendryi (N.L.Gardner) Savoie & Saunders and Savoiea robusta (N.L.Gardner) M.J.Wynne was confirmed based on the anatomy and molecular phylogeny. Additionally, Eutrichosiphonia sp. and Polysiphonia sp. formed separate clades with their representatives, where Polysiphonia sp. had 2% genetic distance from P. determinata. S. robusta is a new record, and Polysiphonia sp. might be a new species. However, Multi-gene analysis with different localities might resolve the species identity. Finally, species belonging to Polysiphonia sensu lato within the San Juan Islands have been updated. Keywords: Maximum