A revision of the genus Lasianthus (Rubiaceae) in Africa, excluding Madagascar

23 species, one subspecies and three varieties have been described or named for the pan-tropical genus Lasianthus Jack (Rubiaceae) in continental Africa. In the present revision thirteen species, five subspecies and one variety are recognized; additionally two hybrids are proposed. Of the previously named taxa, the subspecies is raised to species rank whereas two species are degraded to subspecies and variety status, respectively. Five species are synonymised including two varieties, and four are left with uncertain status, including one variety. The distribution of the genus in Africa consists of two distinct elements: one component is found in the Guineo-Congolian regional centre of endemism and one in the eastern part of Afiomontane Archipelago-like regional centre of endemism. A centre of species diversity is found in Eastern Arc Mts., where six endemic species occur together with L. laxinervis and the more widespread L. kilimandscharicus. Four of the species are strict endemics of the Uluguru Mts. In addition to the presentation of the new section: Lasianthus Sectio Membranacei, sect. nov., this revision contain two hybrids from Uluguru Mts.: L. macrocalyx × pedunculatus and L. cereifizorus × pedunculatus, and following new taxa and new combinations: L. africanus ssp. biokoensis, subsp. nov.; L. africanus ssp. mayumbensis, comb. et stat. nov.; L. kilimandscharicus ssp. glabrescens, ssp. nov.; L. kilimandscharicus ssp. glabrescens var. xanthospermus, comb. et stat. nov.; L. kilimandscharicus ssp. hirsutus, ssp. nov.; L. laxinervis, stat. nov.; L. pedunculatus ssp. angustisepalus, ssp. nov.