Sericanthe etugei and S. onanae (Coffeeae Rubiaceae) new cloud forest tree species Endangered in Southwest Cameroon & Bioko (Equatorial Guinea).

Abstract

Two new species of cloudforest tree are described and illustrated from the Cross-Sanaga Interval within the Lower Guinea Domain. Sericanthe etugei Cheek from South West and Littoral Regions of Cameroon is species from the Cameroon Highlands, and Sericanthe onanae Cheek from South West Region, Cameroon, and Bioko (Equatorial Guinea). Sericanthe etugei is similar to Sericanthe leonardii (N. Halle) Robbr. of DRC (Kivu) and Rwanda, differing in the stipular awn 0.25 mm long (vs 1 - 4 mm), the adaxial leaf midrib and secondary nerves glabrous (vs hairy), the tertiary nerves conspicuously scalariform with the naked eye (vs not visible). The species is also similar to Sericanthe testui var. testui, differing in being a tree (vs liana), with stems not decorticating (vs decorticating), the calyx truncate in bud (vs closed) and in the pubescent ovary (vs glabrous). Sericanthe onanae is similar to S. mpassa Sonke & Robbr. of lowland forest in Gabon, differing from that species in that the leaves have an acumen (0.5 - )0.7 - 0.8(- 1.2) cm long vs 0.3 - 0.5 cm, secondary nerves are 7 - 10 (- 12) on each side of the midrib (vs 4 - 6 in S. mpassa), and that the stipules are 5 - 6.5( - 7) x 3 - 5(- 6) mm ( vs 2.5 mm long) and truncate (vs overtopped by an awn c. 1 mm long). It is also similar to S. jacfelicis (N. Halle) Robbr., differing in that the leaves are smaller (<15 cm long vs 16 - 20 cm long), the abaxial surface of the leaf blade has 7 - 10( -12) lateral nerves on each side of the midrib (vs 5 -7) and has a glossy surface and papery texture (vs matt, coriaceous), the petioles are hairy (vs glabrous), the stipules are 5 - 6.5( - 7) mm long, truncate, lacking an awn or arista, (vs 3 -4 mm long, with an arista 0.5 - 1 mm long). These two new species are both provisionally assessed as Endangered EN B2ab(iii) with the 2012 IUCN standard. The new species are briefly discussed in the context of other newly discovered submontane species from the Cross-Sanaga Interval. We speculate that the seeds of these species may be primate-dispersed.