CONGRUENCE AND CONSENSUS IN THE COTTON TRIBE (MALVACEAE)

We explored the evolutionary history of the Gossypieae and Gossypium u sing phylogenetic analysis of biparentally and maternally inherited ch aracters. Separate and combined data sets were analyzed and incongruen ce between data sets was quantified and statistically evaluated. At th e tribal level, phylogenetic analyses of nuclear ribosomal ITS sequenc es yielded trees that are highly congruent with those derived from the plastid gene ndhF, except for species that have a reticulate evolutio nary history or for clades supported by few characters. Problematic ta xa were then pruned from the data sets and the phylogeny was inferred from the combined data. Results indicate that 1) the Gossypieae is mon ophyletic, with one branch from the first split being represented by m odem Cienfuegosia; 2) Thespesia is not monophyletic, and 3) Gossypium is monophyletic and sister to an unexpected clade consisting of the Ha waiian genus Kokia and the east African/Madagascan genus Gossypioides. Based on the magnitude of ndhF sequence divergence, we suggest that K okia and Gossypioides diverged from each other in the Pliocene, subseq uent to their apparent loss of a pair of chromosomes via chromosome fu sion. Phylogenetic relationships among species and ''genome groups'' i n Gossypium were assessed using cpDNA restriction site variation and I TS sequence data. Both data sets support the monophyly of each genome group, once taxa known or suspected to have reticulate histories are p runed from the trees. There was little congruence between these two da ta sets, however, with respect to relationships among genome groups. S tatistical tests indicate that most incongruence is not significant an d that it probably reflects insufficient information rather than a bio logical process that has differentially affected the data sets. We pro pose thai the differing cpDNA- and ITS-based resolutions of genome gro ups in Gossypium reflect temporally closely spaced divergence events e arly in the diversification of the genus. This ''short internode'' phe nomenon is suggested to be a common cause of phylogenetic incongruence .