Clarifying the Dioscorea buchananii Benth. species complex: a new potentially extinct subspecies for South Africa

The Dioscorea buchananii complex is shown to comprise three species, one of which is divided into two subspecies, based on morphological data. Two species, D. rupicola Kunth and D. multiloba Kunth, are endemic or subendemic to South Africa and of widespread occurrence in KwaZulu Natal. They differ markedly from each other in inflorescence and floral morphology and appear to be ecologically differentiated. The third species, D. buchananii Benth., is primarily found in southeastern tropical Africa, but a small number of specimens collected in South Africa in the late 19^th and early 20^th centuries are placed in an endemic subspecies, D. buchananii subsp. undatiloba (Baker) Wilkin. The latter taxon is a high priority in terms of rediscovery and conservation. Keys, descriptions, supporting information and illustrations are provided and made available online through eMonocot biodiversity informatics tools. Three nomenclatural acts are undertaken: two names are placed in synonymy and a new combination made.