Phylogenetic Systematics of Ipomoea (Convolvulaceae) Based on ITS and Waxy Sequences

Abstract

Ipomoea is a large and complex genus containing over 600 species of vines and shrubs widely distributed throughout the tropics and subtropics. The phylogeny of 40 species representing the three cur- rently recognized subgenera and nine sections within the, genus was analyzed using sequences of the internal 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. Nucleotide data from each gene or region were analyzed singly and in combination using parsimony. Exon and intron sequences from the relatively unexplored waxy gene provided appreciable levels of site mutations, and intron sequences revealed several phylogenetically informative de- letions. ITS provided greater resolution and was largely congruent with waxy. Combined analyses using Merremia and Operculina as outgroups showed strong support for two major clades, including a novel assem- blage of four Old World species and a larger clade composed of the remaining sample. Within the larger clade were numerous well-supported subclades, several of which corresponded to previously recognized taxonomic groups. Higher level hierarchical relationships within the two clades and the among the subclades did not support the most recent classification scheme, which divides Ipomoea into three subgenera, Ipomoea, Quamoclit, and Eriospermum. A striking result from this study was identifying a close relationship between species of section Pharbitis (subgenus Ipomoea) and species of subgenus Quamoclit. This clade is comprised of taxa with a broad range of morphological diversity, implying both floral and vegetative morphology may have been evolutionarily labile within the genus. The composition of three clades consisting largely of species of subg. Eriospermum suggests a novel set of relationships between New World and Australian species. Several clades identified in this study are prime candidates for future studies of character evolution, including several putative cases of independent pigment transformations of red and white flowers from purple flowers.