Taxonomy of Wiborgiella (Crotalarieae, Fabaceae), a Genus Endemic to the Greater Cape Region of South Africa

A taxonomic revision of the recently described genus Wiborgiella is presented. Nine species are recognized within the genus, two of which are newly described, W. dahlgrenii and W. vlokii. The genus is endemic to the Cape region of South Africa and most species are highly localized and rare. Wiborgiella species can be distinguished from other genera in the tribe Crotalarieae by a combination of brown young branches (early formation of bark in the stems of the perennial species), laminar trifoliolate leaves, glabrous petals, a 4 + 6 anther arrangement, and oblong, wingless, inflated fruit. Anatomical studies revealed that all species of the genus have dorsiventral leaves (mesophyll differentiated into palisade parenchyma adaxially and spongy parenchyma abaxially) with mucilage cells in the epidermis which distinguishes Wiborgiella from other closely related genera, such as Calobota which has isobilateral leaves without mucilage cells. The fruits of Wiborgiella species are all thin-walled, have highly sclerified mesocarps and mucilage cells are present in some species. These fruit character states are also present in other genera of the Crotalarieae. The taxonomic treatment of the genus includes a key to the species, descriptions, illustrations, nomenclature, typification, and geographical distribution of each species.