The tree species Cryptosepalum korupense Burgt, sp. nov. (Leguminosae: Caesalpinioideae) is described and illustrated. Cryptosepalum korupense, sp. nov. is related to C. staudtii Harms. Cryptosepalum korupense, sp. nov. has (10-)14-21(-26) pairs of leaflets; C. staudtii has 10-14(-16) pairs of leaflets. The placement of the midvein of the small, emarginate leaflets of C. korupense, sp. nov. distinguishes the species from all other West and Central African Caesalpinioideae species. Cryptosepalum korupense, sp. nov. trees can grow to 44 m high and 88 cm trunk diameter. The new species presents ballistic seed dispersal and grows gregariously; a map of a group of 14 trees is presented. Cryptosepalum korupense, sp. nov. is endemic to the Southwest Region in Cameroon. In southern Korup National Park 18 trees over 10 cm trunk diameter were found during the mapping of c. 11.2 km² of forest. Of the trees over 50 cm trunk diameter, one tree out of c. 3100 trees is C. korupense, sp. nov. The new species was also found along the banks of the Idu River near the village Besingi, and in the lowland forests northwest of Mount Cameroon. Cryptosepalum korupense, sp. nov. is assessed as Endangered (EN) and C. staudtii as Least Concern (LC) under the criteria of the IUCN.