Solanum section Aculeigerum (the Solanum wendlandii group, Solanaceae) comprises eight species ranging from Mexico and Central America to Ecuador and Peru with one species in southeastern Brazil, Paraguay and northern Argentina. One species, Solanum wendlandii, is commonly cultivated worldwide in tropical and subtropical regions, and one new species from southern Mexico, Solanum triunfense, is described here. Members of Solanum section Aculeigerum are differentiated from other sections of Solanum by a combination of plurifoliate sympodial units, branched inflorescences, presence of prickles coupled with absence of stellate trichomes, and a vine-like habit. Unlike most other prickly species of Solanum, which are placed into Solanum subgenus Leptostemonum, they lack stellate hairs, and phylogenetic studies suggest that the section is one of several potential sister groups for the spiny solanums. A key, descriptions, habitat and distribution data, preliminary conservation assessments, specimens examined and illustrations are provided for all species in Solanum section Aculeigerum. Lectotypes are designated for the following five names: S. aculeolatum M. Martens & Galeotti, S. mazatenangense Coult. & Donn. Sm., S. molinarum J. L. Gentry, S. pachyandrum Bitter, and S. sagranum A. Rich., and neotypes are designated for S. glaucescens Zucc. and S. wendlandii Hook. f.