Dioecy, the occurrence of separate female (pistillate) and male (staminate) plants in a species, has evolved in about 15% of the world's flowering plants. Schiedea and Alsinidendron of the carnation family (Caryophyllaceae) provide an excellent opportunity to study the evolution of dioecy on the Hawaiian Islands. Eight of the 22 species of Schiedea show varying stages in the evolution of dioecy (collectively these breeding systems are termed diclinous). The apparently high frequency of dicliny on remote oceanic islands has been used to support several contrasting hypotheses about the evolution of dioecy. Distributional data alone are difficult to decide the matter, without knowing whether dicliny has evolved in situ on the islands and whether it has evolved multiple times there. Drs. Weller and Sakai of the University of California at Irvine will study evolutionary relationships in these two genera using morphological, chromosomal, and molecular data. The use of DNA analyses to reconstruct phylogenetic relationships will provide an independent assessment uncomplicated by convergent evolution of floral morphology that may be associated with breeding systems. A phylogeny of Schiedea and Alsinidendron will increase understanding of the basic evolutionary forces associated with adaptive radiation in these diverse genera and help in interpreting novel features found in the group, including specialized floral nectaries, vines, and fleshy fruiting structures. Information on the evolution of dicliny is also of general interest because of the potential importance of these breeding systems in crop species. A number of species of Schiedea and Alsinidendron are believed extinct in Hawaii, and the information obtained in this research will be useful for interpreting relationships among breeding systems, rarity, and the likelihood of extinction in plants.
