Numerous problematic and historically neglected plant genera in southern Africa are in urgent need of revision. This paper represents a taxonomic revision of Portulaca L., of the monogeneric family Portulacaceae, in southern Africa. Portulaca has not been revised in the study area since 1862. Both field-collected and herbarium specimens were studied in the present investigation. Ten species of Portulaca are recognised in southern Africa: three naturalised (P. grandiflora Hook., P. obtusa Poelln., and P. oleracea L. aggregate), and seven indigenous (P. hereroensis Schinz, P. kermesina N.E.Br., P. quadrifida L., P. pilosa L., P. trianthemoides Bremek., P. waterbergensis Peckover, and P. wightiana Wall. ex G.Don). Two species (P. trianthemoides and P. waterbergensis) are endemic to the region and found only in the Limpopo province of South Africa. An identification key for all southern African Portulaca species is presented, along with revised descriptions, diagnostic characters, geographic distributions, and habitat information.