Phylogeny of Hymenophyllum subg. Mecodium (Hymenophyllaceae), with special focus on the diversity of the Hymenophyllum polyanthos species complex

Hymenophyllum subg. Mecodium (Hymenophyllaceae) is represented by ca. 35 epiphytic species. Past reports suggest that Hymenophyllum polyanthos (Sw.) Sw., a pantropical species, does not represent a monophyletic grouping as it is recognized today. This research focuses on the H. polyanthos species complex, while comparing it to other species of subg. Mecodium using molecular and morphological traits. Here, chloroplast gene sequences of the atpB, atpB–rbcL–accD, rps4–trnS, and matK regions of 132 samples are compared under phylogenetic analyses and the resulting trees are discussed according to distributional and morphological differences. As a result, two big clades can be observed within Mecodium: one represented by plants distributed through Malesia, Australia, Pacific islands, Indian Ocean, and southern South America, and the other represented by plants occurring in Central and South America, Africa, and Asia. Hymenophyllum polyanthos samples appear interspersed in the phylogeny, evidencing its polyphyletic status. Main lineages identified here as H. polyanthos include: (1) plants from the Neotropics, closely related to species like H. myriocarpum Hook. and H. undulatum Sw., and probably representative of the type lineage for the species; (2) several independent lineages within the Asian samples; and (3) two distinct lineages distributed from Malesia and Pacific regions to South and Central America. The combination of distributional patterns and a morphological analysis of seven leaf traits suggests that these lineages are mostly sympatric and show a morphological variation that overlaps with each other.