The taxonomy of Ipomoea section Batatas is summarized with the conclusion that the alliance is composed of twelve named species, two named hybrids and one unnamed hybrid. An interpretation of evolution within the section is presented by using data from morphology, ecology, cytology, hybrids, and cluster analyses. Genetic diversity is discussed in relation to data on the phytogeography of the section. An hypothesis of the origin of the sweet potato is given with the conclusion that I. triloba and I. tifida are its closest extant relatives. A nomenclator of important binomials and their current disposition is appended.