Ipomoea section Pharbitis is a small group of morning glories recognizable by a three-locular capsule and herbaceous sepals. A comprehensive taxonomic revision was undertaken to improve the understanding of the systematics of these species. Phylogenetic data from two molecular markers (ITS and trnD-trnT) and morphological characters supported the monophyly of sect. Pharbitis. This study identified seven monophyletic species and two species-complexes, the focus of the revision. Relationships were unresolved for three named species. In conjunction with the revision, an artificial hybridization experiment was performed involving eight populations of the 'I. hederacea'-'I. nil' species -complex. All populations did not constitute a panmictic unit, nor did crossability follow the pattern expected for two distinct species. Differences in pollen-size and style-length resulted in reduced crossability. Together the results identified interfertile populations, genetic incompatibilities that corresponded to the named species, as well as incompatibilities within named species, and a complex pattern of pollen-style interactions.
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