Morphological variation and its taxonomic and evolutionary significance in the Hawaiian Psychotria (Rubiaceae)

Morphological evidence resulting from a taxonomic revision of the genusPsychotria in the Hawaiian Islands supports previous work which recognized sectionsPelagomapouria andStraussia. The differences between these sections in inflorescence architecture, flower size, anther attachment, and pyrene anatomy, strongly support the contention that at least two introductions to the Hawaiian Archipelago were responsible for the origin of these sections. Whereas the taxa in sectionPelagomapouria are quite distinct from one another morphologically, those in sectionStraussia demonstrate almost continuous morphological intergradation.Straussia taxa also tend to become less distinct when followed from the older to the younger islands of the archipelago. Morphological variation within several complex species is illustrated. The morphological evidence supports the hypothesis thatStraussia has had a shorter tenure in the Hawaiian Islands than hasPelagomapouria and is in a relatively early evolutionary stage of adaptive radiation and speciation.