Acmadenia kamdeboo (Rutaceae: Diosmeae)—A new species endemic to the Kamdebooberge, Sneeuberg Massif (Eastern Cape, South Africa)

• A new species of Acmadenia is described from the Eastern Cape, South Africa. • The new species is endemic to the Kamdebooberge, Sneeuberg. • This is the first species of Acmadenia found on the Great Escarpment. • The species is recommended as South African Red Category of Rare. Acmadenia Bartl. & H.L. Wendl. (Rutaceae: Diosmeae) is a genus of 33 aromatic shrub species, which—with the exception of at least three species—is endemic to the Core of the Greater Cape Floristic Region and contributes to the exceptional richness of the Core of the Greater Cape Floristic Region, which is also part of a biodiversity hotspot. We describe the 34 th known species, A. kamdeboo V.R. Clark & J.D. Vidal—a narrow endemic confined to the Kamdebooberge (Camdeboo Mountains) in the south-western Sneeuberg massif, near Aberdeen (Eastern Cape, South Africa). Morphologically, it is closest to A. sheilae I. Williams, but differs by the smaller, obovate-lanceolate leaves; alternate phyllotaxy; adpressed to patent leaf insertion; shorter sepals and bracts; and a rounded apical anther gland. Also, Acmadenia kamdeboo occurs primarily on Karoo Supergroup dolerites—rather than on Cape Supergroup sandstones. Acmadenia kamdeboo contributes to a local node of endemism in the western Sneeuberg—including the other, highly localised Kamdebooberge endemic Faurea recondita Rourke & V.R. Clark—and is the only Acmadenia found north of the Great Karoo, on the Great Escarpment. Acmadenia kamdeboo is the second Eastern Cape endemic in the genus—both being in summer/bimodal autumn–spring climates—out of three species recorded in the province. The Kamdebooberge deserves further botanical exploration and may contain further novelties.