Phylogenetic systematics of Ipomoea (Convolvulaceae) based on ITS and waxysequences

Ipomoea is a large and complex genus containing over 600 species of vines a nd shrubs widely distributed throughout the tropics and subtropics. The phy logeny of 40 species representing the three currently recognized subgenera and nine sections within the genus was analyzed using sequences of the inte rnal transcribed spacer (ITS) region of nuclear ribosomal DNA and sequences for three exons and two introns of the 3' end of the nuclear gene waxy. Nu cleotide data from each gene or region were analyzed singly and in combinat ion using parsimony. Exon and intron sequences from the relatively unexplor ed waxy gene provided appreciable levels of site mutations, and intron sequ ences revealed several phylogenetically informative deletions. ITS provided greater resolution and was largely congruent with waxy. Combined analyses using Merremia and Opeyculina as outgroups showed strong support for two ma jor clades, including a novel assemblage of four Old World species and a la rger clade composed of the remaining sample. Within the larger clade were n umerous well-supported subclades, several of which corresponded to previous ly recognized taxonomic groups. Higher level hierarchical relationships wit hin the two clades and the among the subclades did not support the most rec ent classification scheme, which divides Ipomoea into three subgenera, Ipom oea, Quamoclit, and Eriospermum. A striking result from this study was iden tifying a close relationship between species of section Pharbitis (subgenus Ipomoea) and species of subgenus Quamoclit. This clade is comprised of tax a with a broad range of morphological diversity, implying both floral and v egetative morphology may have been evolutionarily labile within the genus. The composition of three clades consisting largely of species of subg. Erio spermum suggests a novel set of relationships between New World and Austral ian species. Several clades identified in this study are prime candidates f or future studies of character evolution, including several putative cases of independent pigment transformations of red and white flowers from purple flowers.