Raphia gabonica Mogue, Sonke & Couvreur, 2018

Kamga, Suzanne Mogue, Niangadouma, Raoul, Stauffer, Fred W., Bonaventure Sonke, & Couvreur, Thomas L. P., 2018, Two new species of Raphia (Palmae / Arecaceae) from Cameroon and Gabon, PhytoKeys 111, pp. 17-30 : 18-19

Raphia gabonica Mogue, Sonke & Couvreur sp. nov. Figures 1 , 2

Type.

Gabon. Moyen Oogoué: 5 km from Alèmbé on national road in the direction to la Lope, 0.07916S, 11.00836E, 228 m a.s.l., 18 November 2015, Mogue K.S. 22 (holotype: WAG; isotypes: LBV, YA).

Diagnosis.

Raphia gabonica closely resembles R. gentiliana by its solitary stem with curly fibres and the shape of the partial inflorescences. Raphia gabonica differs from R. gentiliana in being a mainly tierra firme species (vs. a swamp species), the shape of its fruits being globose, deltoid or ovoid (vs. ellipsoid) with 11 or 12 rows of scales (vs. 9-11) and a thick mesocarp measuring>8 mm.

Description.

Stem 3-7 m tall, 20-30 cm in diameter, solitary; dead leaf sheaths persistent; trunk covered by fibres and old leaf sheaths; fibres formed through disintegration of leaf sheath margins ca. 1-2 mm in diameter, curly, dark brown to grey. Leaves 7 or 8, 8-13 m long in total, horizontal, then arching downwards towards the apex; sheath 80-140 cm long, 15-30 cm wide basally, channelled, smooth, margin fibrous, light brown with black and grey spots; petiole 1.7-4 m long, 7-10 cm in diameter basally, channelled, smooth, brown with dark and grey spots, green at younger stages; rachis 5-7 m long, channelled basally and keeled towards the apex, smooth, no spines on keel, light brown to brown, spotted black and grey; pinnae 170-195 per side, irregularly arranged in 4 planes, arching downwards towards the apex, extreme basal pinnae 55-70 cm long, 1.2-1.3 wide, filiform, middle pinnae 1.10-1.20 m long, 4.5-5 cm wide, linear, apical pinnae 9-23 cm long, 0.6-2.4 cm wide, linear, midrib prominent adaxially, brown spines along pinnae midrib and margins, older pinnae bearing spines more basally, younger ones throughout the pinnae, pinnae adaxial surface dark green, abaxial surface waxy green. Leaves next to inflorescence reduced with split sheaths. Inflorescences 5, pendulous, 1.2-1.8 m long, 9 - 10 cm (young) to 30-35 cm (mature) in diameter at base (including rachillae); light brown to brown; prophyll tubular, bearing 2 keels merging to form a pointed beak; peduncle 20-25 cm long, 7-8 cm in diameter, dorsi-ventrally compressed, smooth dark brown abaxially; penduncular bracts 8-20, tubular with triangular apices, smooth, dark brown abaxially; rachis 1.40-1.60 m long, bearing numerous bracts rarely empty, 50-70 first order rachillae, moniliform in shape, circular, alternating in 2 rows on each side of the rachis, smooth, prophyllar bract at the base of first order rachillae, tubular, bearing 2 keels at the side, smooth; basal first order rachillae 30-40 m long, 1.5-2 cm in diameter excluding rachillae, 25-30 cm including second order rachillae, bud flattened; prophyllar bract at the base bearing 2 keels on both sides, other bracts bearing flowers, rarely empty; second order rachillae ca. 38 per side, basal second order rachillae 15-19 cm long, 0.3-0.5 cm in diameter, middle second order rachillae 9-12 cm long, 0.4-0.5 cm in diameter, apical second order rachillae 2.5-5 cm long, 0.3-0.4 cm in diameter, circular, alternating in 2 rows on each side of first order rachillae, bud 1.5-1.7 cm long, flattened, smooth; middle first order rachillae 27-30 cm long, 1.5-2 cm in diameter excluding rachillae, 20-22 cm including second order rachillae, bud flattened; prophyllar bract at the base bearing 2 keels on both sides, other bracts bearing flowers, rarely empty; second order rachillae ca. 33 per side, basal second order rachillae 14-15 cm long, ca. 0.5 cm in diameter, middle second order rachillae 8.5-9 cm long, ca. 0.5 cm in diameter, apical second order rachillae 2.5-3 cm long, ca. 0.5 cm in diameter, circular, alternating in 2 rows on each side of first order rachillae, bud flattened, smooth; apical first order rachillae: 17-20 cm long, 1-1.5 cm in diameter excluding rachillae, 7-10 cm including second order rachillae, bud flattened; prophyllar bract at the base bearing 2 keels on both sides, other bracts bearing flowers rarely empty; second order rachillae 20 per side, basal second order rachillae 4-7 cm long, 0.2-0.3 cm in diameter, middle second order rachillae 4-5 cm long, 0.2-0.3 cm in diameter, apical second order rachillae 2.5-3.5 cm long, 0.2-0.3 cm in diameter, circular, alternating in 2 rows on each side of first order rachillae, bud flattened, smooth, light brown. Flowers: only very old or very young flowers observed, solitary, exerted, arranged in one row (sometimes two) on each side of second order rachillae, staminate flowers distal, pistillate flowers basal, stamens 6. Fruit: ca. 4 cm long, 3.5 cm in diameter, beak 0.5 cm; globose, deltoid or ovoid; scales arranged in 11 or 12 rows, shallowly furrowed, dark green to brown when young, turning orange-red at maturity; mesocarp ca. 0.8 cm thick, yellow; seeds 1-3, circular covered in a white coating.

Ecology.

Raphia gabonica occurs in lowland rain forests, growing on hill sides on tierra firme and also near streams. Seen occurring together with Sclerosperma mannii H.Wendl. and Elaeis guineensis A.Chev.

Distribution.

Lower Guinea subcentre of endemism ( White 1979). Raphia gabonica is restricted to the northern part of the Ngounié region in Gabon occurring in very small populations in forests. Altitude 76-228 m (Fig. 3 ).

Preliminary conservation status.

Endangered: EN B2ab(ii): Raphia gabonica is a rare species collected from two close locations in central Gabon (Fig. 3 ). Its minimal area of occupancy (AOO) is estimated to be 8 km2 (within the limits for Critically Endangered status under criterion B2). To date, two locations are known within the limits of the Endangered status. Both collections were made recently (2015) along important road axes (e.g. Nationale 1) and in unprotected areas (Fig. 3 ). For each location, several individuals were seen indicating no immediate threat. However, we project that the ongoing loss of its natural habitat linked to increased human activity will induce an important decline of its EOO and AOO. Raphia gabonica is therefore assigned a preliminary status of EN B2ab(ii), joining the almost 5% of continental African palms under this category ( Cosiaux et al. 2018)

Uses.

No uses have been reported for this species.

Notes.

Raphia gabonica appears to belong to the moniliform section of Otedoh (1982) linked to the shape of its partial inflorescences. However, the solitary trunk with curly fibres could also suggest a resemblance to species within the temulentae section (e.g. Raphia hookeri G.Mann & H.Wendl. or R. sese De Wild.).

Additional specimen examined.

Gabon. Ngounié: Zamata village along national road N1, 1.03044S, 10.51881E, 76 m a.s.l., 19 Nov 2015, Mogue K.S. 23 (LBV, WAG,).

Figures

Figure 1. Raphia gabonica, illustrations. A Habit (bar = 1 m) B Details of trunk - notice curly fibres C Detail of full inflorescence D Detail of base of inflorescence E Penduncular bracts F Partial inflorescence with old flowers G Detail of basal part of rachillae with old female flower H Detail of apical part of rachillae with old male flowers (Scale bar: 1 cm) I Partial inflorescence with fruits J Fruit K Longitudinal section of fruit. Drawings based on A from Mogue 22 B-J Mogue 23. Drawings by Hans de Vries.

Figure 2. Raphia gabonica in natural habitat (Alembe, Gabon). Notice dry land habitat, not growing in colonies, single stem with curly fibres and long pendulous inflorescences. Photo: Thomas L. P. Couvreur.

Figure 3. Distribution of Raphia gabonica and R. zamiana.