(Annonaceae) a new tree species with notes on its pollination biology, and the Critically Endangered narrowly endemic plant species of the Ebo Forest, Cameroon.

Background: The Ebo Forest area is a highly threatened centre of diversity in the Littoral Region of Cameroon, globally important for conservation with many threatened species including 68 threatened species of plant, yet not formally protected. The tropical African evergreen forest tree genus Engl. & Diels (Annonaceae) is characterised by unisexual, usually cauliflorous flowers with a uniseriate corolla of four petals, and two sepals. Cameroon is the centre of diversity of the genus with 14 of the 19 known species.

Methods: The herbarium collection 51 from Ebo is hypothesized to represent a new species to science of . This hypothesis is tested by the study of herbarium specimens from a number of herbaria known to hold important collections from Cameroon and surrounding countries.

Results: We test the hypothesis that 51 represents a new species to science, using the most recent dichotomous identification key, and comparing it morphologically with reference material of all known species of the genus. We make a detailed comparative morphological study focussing on three other Cameroonian species, and the sympatric . In the context of a review of the pollination biology of , we speculate that in a genus otherwise with species with dull, flesh-coloured (pink, red to brown) flowers pollinated (where known) by diptera, orthoptera and blattodea (flies, crickets and cockroaches), the glossy, pale yellow-green flowers of , with additional traits unique in the genus, may be pollinated by nocturnal moths. Based on 51, we formally name Cheek & Gosline (Annonaceae) as new to science, and we describe, and illustrate, and map it. Restricted so far to a single site in evergreen forest in the Ebo Forest, Littoral Region, Cameroon, is provisionally assessed as Critically Endangered using the IUCN, 2012 standard because the forest habitat of this species remains unprotected, and there exist imminent threats of logging and conversion to plantations.

Discussion: We show that the highest density of species of the genus (12), and of narrow endemics (5), is found in the Cross-Sanaga Interval of SE Nigeria and Western Cameroon. A revised key to the 14 Cameroonian species of is presented. We review the other seven narrowly endemic and threatened species unique to the Ebo forest of Cameroon and discuss the phytogeographic affinities of the area.

Conclusions: adds to the growing list of species threatened with extinction at Ebo Forest due to current anthropogenic pressures.