The tree tomatoes (Solanum section Pachyphylla; formerly genus Cyphomandra) and their close relatives (Solanum section Cyphomandropsis) include about 50 species native to the neotropics. Species boundaries within the group have been clarified, but phylogenetic hypotheses have not been postulated for intra- and intersectional relationships, and the position of the tree tomato clade within the huge genus Solanum has not been resolved. Within section Pachyphylla, Solanum betaceum is particularly engimatic. This species is thus far known only from cultivation, and its place of origin is unclear. Molecular evidence from nuclear and chloroplast sequences coupled with morphological studies and data from recent field work indicate that S. betaceum is most closely related to a complex of Bolivian species, and thus is most likely of southern Andean origin. Molecular phylogenies constructed for a subset of the taxa support the monophyly of section Pachyphylla, with section Cyphomandropsis as a paraphyletic grade. Together, the two sections form a monophyletic group, defined by very large chromosomes and large amounts of nuclear DNA. Species groups within section Pachyphylla identified by sequence data are largely congruent with those based on morphology and crossing studies. Within the genus Solanum, the tree tomatoes and their relatives are most closely related to a clade that includes the spiny solanums. The swollen anther connective and associated male euglossine bee pollination syndrome have originated or been lost more than once in the tree tomato group sensu lato.

Key words: Cyphomandra, phylogeny, Solanaceae, Solanum, tree tomato