Vepris onanae (Rutaceae), a new Critically Endangered cloud-forest tree species, and the endemic plant species of Bali Ngemba Forest Reserve, Bamenda Highlands Cameroon.

We revise and update the records of strict and near-endemic species of the Bali Ngemba Forest Reserve, the largest known surviving patch (c. 8 km in area) of submontane or cloud forest in the Bamenda Highlands, Cameroon which have lost >96 % of their original forest due to human activities. Nine strict endemics, and 11 near endemics are now documented, a drop from the number recorded after the first survey in 2004, since when five of the provisionally named species have been validly published. We test the hypothesis that a further one of the provisionally named putative Bali Ngemba new species, sp. A, an 8 – 20 m tall tree from cloud forest in the 1310 – 1700 m altitudinal band, is indeed new to science. We compare it morphologically with other multicarpellate, apocarpous, trifoliolate Cameroon tree species formerly placed in the genus Pierre until they were subsumed into by Mziray (1992). These are (Engl.) Mziray and (Pierre) Mziray. We conclude that sp. A is a new undescribed species here named as . The new species is illustrated, mapped and its conservation status assessed as Critically Endangered using the 2012 IUCN standard due to severe fragmentation and the threats of habitat clearance from agricultural pressures at its three locations all of which remain formally unprotected. appears unique among the Guineo-Congolian African oricioid species of in that it occurs in cloud forest, the other species, apart from (G.C.C.Gilbert) Mziray of the Albertine Rift, occurring in lowland forest. It also differs in the very broad, (7.8 –) 11.3 – 18 cm wide leaflets of the flowering stems which have a 6 – 18 (– 30) mm long, narrowly triangular acumen (vs leaflets <12 cm wide, acumen absent or short) and in having both subsessile and pedicellate (pedicels 0.25 – 0.3 mm long and 1 (– 2) mm long) male flowers (vs male flower pedicels all sessile, or all c. 3 mm long). We report for the first time on stage-dependent leaf heteromorphy in and characterise a level of sexual dimorphism more advanced than usual in the genus. We highlight the importance of protecting Bali Ngemba and other forest patches in the Bamenda Highlands if species such as are not soon to become extinct.