CHLOROPLAST DNA RESTRICTION SITE STUDY OF VERBESINA (ASTERACEAE, HELIANTHEAE)

Chloroplast DNA variation was examined for 79 species of Verbesina and 24 outgroups. Two independent analyses of the data were performed. An intergeneric study to elucidate the phylogenetic relationships of Ver besina used 22 genera, most of which are regarded in the literature as closely related to Verbesina. Coreopsis and Hymenoxys served as outgr oups for this analysis. The 16 6-bp (base pair) restriction endonuclea ses used in the intergeneric study revealed 263 phylogenetically infor mative sites. Wagner analyses of these characters resulted in four equ ally parsimonious trees with a length of 857 steps and a Consistency I ndex of 0.492. Results from this study indicate that Verbesina is mono phyletic, a member of the tribe Heliantheae, and that its sister taxa are the mostly Mexican genera Podachaenium, Squamopappus, and Tetrachy ron. The infrageneric study of Verbesina included species belonging to all of its infrageneric taxa, except the monotypic sect. Stenocarpha. The 17 6-bp restriction endonucleases used in the infrageneric study revealed 137 sites 77 of which were phylogenetically informative. Wagn er analyses of these characters generated 180 equally parsimonious tre es with a length of 158 steps and a Consistency Index of 0.786. The ge nera Podachaenium, Squamopappus, and Tetrachyron served as outgroups. Two major clades, which correspond to traditional divisions of the gen us based on leaf arrangement, are supported by the study. No support w as found for the monophyly of seven of the 11 sections examined; furth er sampling of sections Lipactinia, Ochractinia, Verbesina, and Ximene sia is needed. Results support a major reassessment of the traditional infrageneric classification of the genus and provide the basis for th e reevaluation of the sectional taxonomy of Verbesina. These studies s upport a North American origin for the genus with several independent introductions into South America producing significant diversity, espe cially in the Andean region.