In the Hawai`ian archipelago, the genus Melicope (Rutaceae) has undergone an extensive radiation. Although one of the largest angiosperm genera in the islands with ~48 species, these Melicope species have lacked any recent revisionary or phylogenetic study. Based on morphological characters, the Hawai`ian and related Marquesan species have been assigned to section Pelea by Hartley, but species delimitations within that group are unclear, as many of the taxa currently recognized as species may only be distinctive geographical forms of widespread species. Other questions of interest in this group are the number and nature of introductions of Melicope into these islands and the possible inclusion of the endemic Hawai`ian genus Platydesma as a highly derived member of Hawai`ian Melicope . We have produced an initial molecular phylogeny focussing on Hawai’ian and Marquesan taxon relationships using the nuclear ribosomal ITS spacer and the chloroplast trn L region. Four most parsimonious trees were obtained in a maximum parsimony branch-and-bound search. All four indicated a single origin for the Hawai`ian Melicope including Platydesma . The Hawai`ian islands as source area for introduction to the Marquesan archipelago, previously unconfirmed for any other taxa, also are supported by the molecular trees.

Key words: island biogeography, nuclear and chloroplast gene spacers, plant molecular systematics