Résumé
Background and aims – While conducting a taxonomic revision of the genera Diaphananthe and Rhipidoglossum (Orchidaceae), a new taxon from Equatorial Guinea and Cameroon was discovered, and is formally described here.Methods – A comparison of about 800 specimens with the nomenclatural types and the specimens housed at BR, BRLU, K, P, WAG and YA herbaria was undertaken in order to confirm the taxonomical status of the new taxon. Its conservation status was assessed using the IUCN Red List Categories and Criteria.Key results – Rhipidoglossum montealenense Descourvières, Stévart & P.J. Cribb sp. nov., here described and illustrated, is endemic to Río Muni (Equatorial Guinea) and southern Cameroon. The species is found in the mountainous area situated along the transition from the coastal and to the continental regions of Atlantic Central Africa. It is close to R. melianthum but differs by its decurrent petals, a small ovary and a comparatively short spur. The species also differs from R. paucifolium by its elliptical lip lacking a callus and by rounded to subacute sepals and petals, and from R. rutilum by its short leaf internodes. The species is considered as Endangered according to IUCN Categories and Criteria. Its survival in situ will likely depend on the maintenance of the subpopulation in the Monte Alén National Park.