The genus Boerhavia in southern Africa is revised. Eight species and one infraspecific taxon are recognized for the Flora of Southern Africa region, with Boerhavia orbicularifolia Struwig described as new. Four of the species are indigenous, with three endemic to semi-arid parts of Namibia and north-western South Africa. The eight species can be distinguished from one another by the shape and indumentum of the anthocarp. The majority of taxa have no edaphic preferences but Boerhavia repens subsp. repens is associated with high Mg levels. This is a first attempt at a comprehensive taxonomic revision for the genus in southern Africa, and includes a key to the species, complete nomenclature, and a description of all the infrageneric taxa. Taxon accounts are supplemented with geographical distribution records, notes on the ecology, soil preferences and known traditional uses. Keywords: Anthocarp, Boerhavia, Morphology, Nyctaginaceae, Soil chemistry, Southern Africa, Taxonomy.