Abstract
Summary We describe Microcos rumpi (Grewiaceae) a massive new species to science from the Rumpi Hills of SW Region Cameroon, a proposed Tropical Important Plant Area. Confined on current evidence to submontane forest, the species is threatened by expanding habitat clearance for farms and is assessed as Critically Endangered. A large tree, attaining 35 – 40 m height, and 80 cm trunk diam. at 1.3 m above ground, its biomass is calculated as in the range of 7 – 8 metric tonnes. It is the third tree species of the genus recorded from Cameroon and only the fourth recorded west of D.R. Congo. A key to these four species is presented. The concept of Microcos in Africa in relation to Grewia is discussed, and three new combinations are made, transferring three species names from Grewia to Microcos : Microcos louisii (R.Wilczek) Cheek, M. evrardii (R.Wilczek) Cheek and M. schmitzii (R.Wilczek) Cheek.