A systematic monograph is presented for Hydnora (Hydnoraceae), a poorly known genus of holoparasitic plants distributed across Africa, Madagascar and southern Arabia. Species of Hydnora are characterised by their underground habit, unusual feshy fowers and complete absence of leaves or photosynthetic tissue. This is the frst detailed monograph of the genus Hydnora since 1935 and is informed by a comprehensive survey of herbarium specimens and literature. Detailed descriptions, full synonymy, distribution maps and discussion concerning confusable taxa are provided for each species, along with notes on ethnobotany, ecology and conservation. We place particular emphasis on the taxonomic value of osmophore geometry and positioning in living and dried material, which are highly consistent within species. We also provide the frst detailed assessment of host range across the genus. Hydnora hanningtonii Rendle and H. solmsiana Dinter are reinstated from synonymy, and H. bolinii S.Hatt is newly described here. The infrageneric classifcation is reviewed and a key is provided for both living and dried material. Species are accompanied by both illustrations and photographs of living and dried material where possible. Keywords: Africa, holoparasite, host specifcity, Hydnora bolinii, Hydnora hanningtonii, Hydnora solmsiana, monograph, parasitic plant.