A new coffee species from South-West Cameroon,the principal hotspot of diversity for Coffea L.(Coffeeae, Ixoroideae, Rubiaceae) in Africa

Coffea rizetiana Stoff. & M.Noirot, sp. nov., a diploid species only known from a single wild population in South-West Cameroon, is formally described here. It is probably extinct in the wild, but is present in the germplasm collection in Bassin Martin (Réunion, France) and Meise Botanic Garden (Belgium). Phylogenetic analyses reveal a close relationship with C. montekupensis Stoff., a species endemic to the same region but occurring at higher elevations, and with C. liberica Bull. ex Hiern, a species with a wide Central and West African distribution. The new species can be distinguished from other Coffea species from Central Africa by its large black fleshy fruits with thick mesocarp. It can be differentiated from its close relative C. montekupensis by its larger less obovate leaves, longer corolla tube and larger fruits; and from C. liberica by its shorter petiole, acuminate leaf tip, cuneate leaf base, thinner leaf blade, shorter corolla tube, longer corolla lobes and black fruits with a thick fleshy pericarp. The evolutionary importance of the fruit colour is discussed, as well as the role of Mount Kupe, the Bakossi Mountains and the broader South-West Cameroon region as the principal Coffea diversity hotspot on the African continent.