The yam family, Dioscoreaceae is represented in the Caribbean by two genera, Rajania L. (ca. 25 species) and Dioscorea L. (ca.400 spp. worldwide). Rajania, a Caribbean endemic genus is distinguished from Dioscorea on the basis of gross fruit morphology. The fruit of Rajania is a samara, and that of Dioscorea a trilocular capsule. Rajania is distributed from the Lesser Antilles to the Bahamas, with species diversity concentrated in Cuba. Dioscorea species in the Caribbean include six endemics and four species with extra-Antillean distributions in the Americas. Recent phylogenetic studies by Caddick et al (2000) suggest that Rajania was derived from within Dioscorea but its relationship to other Caribbean Dioscorea species was not evaluated, nor was the monophyly of the endemic genus tested. Here we present an expanded sample of the Caddick et al. rbcL data set including Caribbean and other New World yam species not previously evaluated. In preliminary analyses Rajania is strongly supported as monophyletic. It is a member of a larger clade that is comprised primarily of Old World Dioscorea species but that also includes Dioscorea altissima Lam. and D. trifida L. both of which occur in the Caribbean and in South America. The remaining Caribbean Dioscorea species comprise at least two South American lineages only distantly related to Rajania, a conclusion also supported by tuber morphology. Sequence data from the nuclear 5S-NTS are being used to evaluate relationships and biogeographic patterns within Rajania. In the context of the present molecular phylogeny the samara is seen as an innovation upon the Dioscorea groundplan. Comparative anatomical data from developing fruits of both genera are presented and the structural changes involved in the transformation of the fruit type are characterized.

Key words: 5S-NTS, Caribbean, Dioscorea, fruit anatomy, Rajania, rbcL