BHARATHAN, G1*, L RAZ2, and P WILKIN3. 1Ecology & Evolution, SUNY, Stony Brook, NY 11794-5245, U.S.A.; 2New York University Department of Biology, New York, NY 100032, U.S.A.; 3Herbarium, Royal Botanic Gardens, Kew, Richmond, Surrey, TW9 3AE, U.K.. - The true yams, Dioscorea (Dioscoreaceae): phylogenetic analysis of chloroplast nucleotide sequences.
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