Cape stinkweeds: Taxonomy of Oncosiphon (Anthemideae, Asteraceae)

A taxonomic revision of the southern African endemic genus Oncosiphon Källersjö (Asteraceae: Anthemidae) is presented. The genus includes annuals or short-lived perennials with discoid or rarely radiate capitula, a conspicuously swollen corolla tube, and 4 ribbed, non-myxogenic cypselas. The Afrikaans vernacular name stinkruid (stinkweed) is commonly applied to species of this genus in reference to their strong, unpleasant odour. Three of the species are recognised as important herbal remedies in Khoi-San and Cape Dutch enthnobotany. We recognise seven species of Oncosiphon, and report the occurrence of occasional hybrids between O. suffruticosus and O. grandiflorus. The species are distinguished by their vestiture, leaf division, inflorescence structure, floral characters and the indumentum of the involucral bracts. A key to the species, the complete nomenclature, species descriptions, diagnostic characters, and distribution and ecological details are provided.