A taxonomic revision of the Thesium goetzeanum species complex (Santalaceae) from Lesotho, South Africa and Swaziland

The genus Thesium L. is in urgent need of revision and has been identified as a priority genus for taxonomic research in South Africa. The revision of 16 morphologically similar grassland species from Lesotho, South Africa and Swaziland, here referred to as the T. goetzeanum complex, is a first step towards a comprehensive revision of the genus. All members of the complex share the following characters: (1) tepals with a prominent apical beard, (2) anthers attached to the perianth tube with post-staminal hairs, (3) stigmas usually not sessile (rarely sessile in T. gracilarioides A.W.Hill and T. gypsophiloides A.W.Hill), (4) monotelic inflorescences, (5) leaves, bracts and bracteoles leaf-like, not scale-like, (6) stems leafy, not rush-like, and (7) stems and leaves glabrous. A comprehensive study of morphology, type specimens, distribution information, available literature, as well as field observations, indicate that the number of accepted species should be reduced from 16 to 9, including the newly recognised species T. infundibulare N.Visser and M.M.le Roux sp. nov. The first comprehensive description of T. procerum N.E.Br. is also provided. A taxonomic revision of the T. goetzeanum complex is presented, including an identification key, updated nomenclature and typifications, descriptions, diagnostic characters, distribution maps and conservation notes for all nine recognised species.