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Solanum section Petota, the potato and its wild relatives, contains about 200 wild species distributed from the southwestern United States, to central Argentina and adjacent Chile. Although most species occur in South America, a secondary center of diversity peaks at 20 degrees north in the central Mexican highlands, including diploids (2n = 2x = 24), tetraploids (2n = 4x = 48), hexaploids (2n = 6x = 72), and triploid and pentaploid nothospecies. This treatment covers the wild potatoes of North and Central America (United States to Panama). It is a summary of recent morphological and molecular studies of species limits and their interrelationships. We collected herbarium and germplasm samples from all countries harboring wild potatoes in this region and now have access to germplasm of every species. A comprehensive treatment in 1990 recognized 33 species, 12 subspecies, and five nothospecies from the region, partitioned into eight formal taxonomic series. We recognize 25 species and four nothospecies from the region, partitioned into eleven informal species groups. It provides the first formal typification of many of these names, an extensive list of georeferenced localities, a geographic information systems based diversity analysis, and illustrations and maps of all the species.

Species boundaries were assessed by phenetic analyses of morphological data for Solanum sect. Petota series Demissa: S. brachycarpum, S. demissum, S. guerreroense, S. hougasii, S. iopetalum, and S. schenckii. These six hexaploid (2n = 6x = 72) wild potato species grow in Mexico and Guatemala and constitute all the taxa of series Demissa except three pentaploid hybrids involving crosses with species from other series. We also analyzed two species, S. albicans (series Acaulia) and S. verrucosum (series Tuberosa), that are morphologically very similar to some members of series Demissa. We chose these species because S. verrucosum has been hypothesized to be a progenitor in the hybrid origin of all species in series Demissa, and because S. albicans is very similar to S. demissum. The results show that S. albicans, S. brachycarpum, S. demissum, S. schenckii, and S. verrucosum are supported by multivariate analyses, but are inconclusive regarding species boundaries of the rare taxa S. hougasii, S. guerreroense, and S. iopetalum, and more collections are needed to resolve their taxonomic status. Extensive overlap of species-specific character states shows the difficulty of the preparation of keys, diagnosis of taxa, and cladistic analyses in this group. The results also show that S. demissum is phenetically more similar to S. albicans than to other species in series Demissa and that S. verrucosum is similar to S. schenckii, and they question the assignment of these species into series.