XVI International Botanical Congess

The endemic Hawaiian species of Psychotria (Rubiaceae) are of considerable evolutionary interest. Relationships in this group were studied using analyses of nrDNA ITS sequences and RAPD markers. The Hawaiian species are monophyletic, with their closest relatives being subg. Psychotria from the western and central Pacific. Colonization was predominantly from older to younger islands, with a higher incidence of within- vs. between-island speciation. Speciation in island systems may provide a simplified form of the processes occurring in mainland populations, local speciation may be the rule for species with small effective population sizes and low levels of gene flow. The origin of new species from a widespread, basal species (by definition paraphyletic) may be a common occurrence in Psychotria.