A taxonomic synopsis of Heterotis (Melastomataceae), including H. kupensis sp. nov., a threatened species endemic to Mt Kupe, Cameroon.

We provide a synopsis of the African genus Heterotis (Melastomataceae), recognising seven species and including the description of a species new to science Heterotis kupensis Sv. & Cheek (Melastomataceae) known only from Mt Kupe in the South West Region of Cameroon. It differs from all other members of the genus by its tardily caducous, oblong calyx lobes; hastate pedoconnectives on the antesepalous stamens with transversely ellipsoid ventral appendages; the hypanthium covered by hairs with thickened bases as well as filiform appendages on the upper half only; sessile leaf-blades and the yellow centre to the flower. In addition, we select lectotypes for H. prostrata (Thonn.) Benth. and H. fruticosa (Brenan) Ver.-Lib. & G.Kadereit, a second step lectotype for H. buettneriana (Cogn.) Jacq.-Fél. and designate the new name H. welwitschii (Cogn.) Sv. & Cheek to replace the illegitimate H. cogniauxiana (A.Fern. & R.Fern.) Ver.-Lib. & G.Kadereit. Morphological species delimitation between H. decumbens, H. prostrata, and H. rotundifolia is difficult and intermediate specimens are common. Heterotis rotundifolia is widely reported as naturalised and invasive, however many occurrences from outside of mainland Africa actually represent H. prostrata or have intermediate morphology. Heterotis decumbens has been introduced and naturalised in Madagascar and the Mascarene Islands. Distribution, habitat, phenology, taxonomic notes, and preliminary conservation assessments following IUCN Red List criteria are presented along with a key to the species.