The origin and evolution of Dioscorea, the pantropical genus of true yams, are fascinating topics from historical, biogeographic, and morphological points of view. For instance, Burkill (1960) hypothesized an early split within the genus into New World and Old World lineages based on current non-overlap between species ranges in the two regions. However, a recent study of Dioscorea, based on rbcL sequences (Caddick et al. 2000), shows that some species in the New World are more closely related to those in the Old World. This suggests either that lineages with species in both regions have persisted, or, alternatively, that dispersal accounts for the appearance of Old World relatives in the New World. The present study extends sampling to other parts of the chloroplast genome (intergenic spacer between trnT and trnL genes, and ndhF gene) and other sections of the genus (in particular, the putative 'basal' section Stenophora and nested genus Rajania). Our findings are largely congruent with other results and are discussed in the context of the biogeographic hypotheses outlined above.

Key words: chloroplast, Dioscorea, phylogeny, trnTL