Keetia gordonii sp. nov. (Rubiaceae - Vanguerieae) a new species of threatened forest liana from the littoral forest of Gabon

Abstract

Keetia gordonii sp. nov. (Rubiaceae - Vanguerieae) a new species of forest liana from the littoral forest of Gabon is formally described and illustrated as the first endemic species of the genus from that country. On current evidence, the species appears to have three locations and is threatened by forest clearance. It is provisionally assessed using the IUCN 2012 standard as Endangered (EN B2a,b(i-iv). The new species is extremely distinctive within the genus, showing several character states previously unrecorded in Keetia. Keetia gordonii is currently unique in its genus for the massively thick, coriaceous leaf blades seen in the fruiting axillary branches (in this respect resembling a Psydrax Gaertn., vs papery or rarely thinly coriaceous in other Keetia species), and also for the globose, smooth pyrenes (vs ovoid, colliculose in other species), in which the lid crest is so vestigial that it is almost imperceptible (vs lid crest conspicuous in other species). The tanniferous seed endosperm shows a new character state for the genus being present in a continuous, solid layer in the outer part of the seed, rather than being in radial bands or diffuse as in other species of the genus. However, there is no doubt that this taxon is best placed in Keetia as opposed to Psydrax due to the disc concealed deep inside the calyx tube (vs exposed), the presence of a pyrene cap (vs none) and the stipules that lack a well-developed keel (vs keel present). Further, the presence of tanniniferous seed endosperm is not recorded in any other genus of the tribe. Keetia gordonii is currently assigned to the K. hispida species group of Guineo-Congolian Africa.