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Solanum subgenus Leptostemonum (Solanaceae) in continental Africa and Madagascar contains 76 native and 10 introduced species; the native species form part of a monophyletic clade of Old World spiny solanums, while the introduced taxa are from the New World and are members of other spiny Solanum clades. Subgenus Leptostemonum (the spiny solanums) is characterized by the possession of stellate trichomes, long tapering anthers with distally directed pores, and the usual presence of epidermal prickles. African members of subgenus Leptostemonum have long been perceived as difficult due to great morphological variability and lack of modern collections. The treatment is based on the examination of over 10,000 herbarium specimens and on field work in the center of species diversity in the group. All species from the region are included in this treatment to assist with identification. The center of both richness and endemism of native species is in East Africa (with 33 endemic species, focused on Kenya and Tanzania); secondary centers of diversity occur in South Africa (12 endemic species) and Madagascar (10 endemic species). The introduced species are generally widespread and are often invasive weeds, but some are cultivated for ornament. Both a dichotomous key and a synoptic character list are presented to aid with identification of these highly variable species. Full descriptions and synonymies (including designation of lecto- and neotypes), illustrations, distribution maps, and discussion concerning similar and potentially related taxa are provided for all accepted species.
