Phylogenetic relationships within the genus Hypnea (Cystocloniaceae, Rhodophyta): convergent evolution and its implications in the infrageneric classification

Hypnea is a monophyletic genus with a complex nomenclatural and taxonomic history, and is an important commercial source of carrageenan. Phylogenies of this genus have been accessed based primarily on Asian species; however, recent studies performed in South America revealed a great diversity of species, for which phylogenetic relationships need to be evaluated. Three infrageneric sections are recognized in the genus: Pulvinatae, Spinuligerae, and Virgatae; however, morphological and molecular circumscriptions within each section lack clarity. In this study, we analyzed three distinct markers to establish phylogenetic relationships among Hypnea species. To assign each species to the correct section, morphological data were obtained from original descriptions, reference literature, and comparisons with type/topotype and herbaria specimens. Our analyses recovered robust phylogenies for the genus and provided new insights on the taxonomic status and relationships among and within Hypnea species. The combination of three genetic markers increased the resolution and support, resulting in the largest and best-resolved phylogeny of the genus to date. Single and combined analyses revealed that the three sections of the genus Hypnea are taxonomically irrelevant, as currently recognized. Morphological differences are not associated with monophyletic groups and similarities among clades could be better explained by convergent evolution in thallus habit.