Systematics of the tropical shrub genus Psychotria L. (Rubiacaeae): Origins, speciation and breeding systems

Phylogenetic relationships of Psychotria and relatives in the tribe Psychotrieae were examined using nuclear ribosomal ITS sequence data, in the first explicitly phylogenetic analysis of the genus. Results indicated that Psychotria is a broadly paraphyletic group, with species currently assigned to the genus comprising at least five independent lineages. Species assigned to subg. Heteropsychotria are more closely related to other genera in the tribe Psychotrieae than they are to other members of the genus Psychotria. Reorganization of the genus to reflect natural groups supported by the phylogenetic analysis include restriction of Psychotria sensu stricto to include members of subg. Psychotria, subg. Tetramerae and the subtribe Hyndophytinae; elevation to generic rank of the neotropical section Notopleura and the Heteropsychotria + Palicourea clade. Additionally, the Hawaiian Psychotria form a monophyletic group and their closest ancestors can be identified as subg. Psychotria from the western and central Pacific. Systematic relationships within the Hawaiian Psychotria were investigated using phylogenetic analysis of ITS and RAPD markers. Three major lineages which were unresolved at the base could be identified, suggesting extremely rapid radiation of the Hawaiian lineage. Two major clades were identified within sect. Straussia, the greenwelliae and the mariniana clade. A pattern of colonization from oldest to youngest islands was inferred from the phylogeny as well as a much higher incidence of within-island versus inter-island speciation. Lastly, breeding systems of the Hawaiian Psychotria were characterized in the field, and the evolution of breeding systems was inferred using a phylogeny obtained from ITS and RAPD data. Contrary to previous reports, the Hawaiian Psychotria exhibited either hermaphroditic, monomorphic or gynodioecious breeding systems. The ancestral breeding system was hypothesized to be either monomorphic or gynodioecious, based on floral morphology of the Hawaiian Psychotria and breeding systems of species of Psychotria occurring in source areas for the Hawaiian islands. These findings negate the use of the Hawaiian Psychotria as an example of dioecy arising from distyly.