RAZ, LAUREN1,2*, JACQUELINE PEREZ CAMACHO3, DENNIS STEVENSON1, and KENNETH CAMERON1. 1Institute of Systematic Botany, The New York Botanical Garden, Bronx, NY 10458; 2Department of Biology, New York University, New York, NY 10003; 3Instituto de Ecologia y Sistematica, Apartado 8029, Codigo Postal 10800, Carretera de Varona Km 3.5 Capdevila, Boyeros, Habana 8, Cuba. - Systematics and biogeography of Caribbean wild yams (Dioscoreaceae).
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