Carapa akuri Poncy, Forget & Kenfack

Authority

Forget, P.-M., et al. 2009. A new species of (Meliaceae) from Central Guyana. Brittonia. 61 (4): 366-374.

Family

Meliaceae

Scientific Name

Carapa akuri Poncy, Forget & Kenfack

Description

Species Description - Large canopy tree to 35 m tall, cm diam., glabrous. Bole cylindrical, ing high up to 20 m, base swollen, often straight, robust and rounded buttresses 0.5 m high. Bark greyish and smooth young individuals, flaking in rectangular irregular patches in adult trees, reddish slash, exudating a whitish-translucent branches spreading into a dense crown. Leaves paripinnate, crowded at the end of branches, yellowish when young, (40- )60- 115 cm long; petiole 12-28 cm long, base swollen, generally with 2 nectaries; rachis (30-)43-90 cm long, glabrous; leaflets opposite, 6-13 pairs, petiolules 1-2 cm long, lamina of basal pairs of leaflets 9-20 x 5- 10 cm, apical pairs up to 16-56 x 4.5-13 cm, oblong, discolorous, apex rounded to broadly acute, mucronate, the muero flattened laterally, thick and spatulate, glandular, base cunéate to rounded, slightly asymmetrical, midrib prominent beneath, with 8-20 secondary veins on each side, tertiary venation loose and flat. Inflorescences pendulous thyrses, in groups of 6-10 at the end of branches, in axils of undeveloped leaves up to 3 cm long, (35)60-100(120) cm long, very much ramified, lower branches up to 15 cm long, transversely scurfy; peduncle 8-14 cm long. Flowers 1-3, born in axil of a 1 mm long, scaly bract; (4)5-merous, pedicel (1.5- )2 - 3.5 mm long, often angular in section and transversely scurfy; calyx green, lobes nar- rowly triangular to broadly ovate, 1-1.5 mm long, margins ciliolate; petals whitish to yellow-green, free to the base, oblong or obovate, 4- 6 x 2-3.5 mm; staminal tube white, urceolate, 3.5-5 mm long, ca. 4 mm diam., with 10 truncate or more or less emarginate lobes; anthers or antherodes 10, oblong, sessile, alternating with lobes, included with- in the tube, ca. 0.7 x 0.4 mm in carpellate flowers, 0.7-0.9x0.4-0.6 mm in staminate flowers; nectary cushion-shaped, white, 0.7- 1.3x2-3 mm; ovary 5-locular, ovoid to globose in carpellate flowers, 1-1.7 x 1.5- 1.8 mm, conical in staminate flowers, 0.6 - 1.5 x 0.5-1.3 mm; ovules 4 per loculus; style less than 0.7 mm long in carpellate flowers, 1-1.5 mm long in staminate flowers; stigma discoid, yellow, 1.4 - 2mm diameter. Fruit a capsule, green when immature, becoming brown at maturity, globose to ovoid 7-11 x 6-17 cm, apex often conspicuously acuminate; valves with more or less developped warty excrescences and numberous extrafloral nectaries, seeds 2.5 - 4.8 x 3 - 5.5 cm, up to 4 per valve; hilum oval, 4.5 -12 x 1.5 - 6mm; testa brown and smooth. seedlings; epicotyl 30-50 cm tall, the first leaves simple, blades discolorous, the adaxial surface pale greyish green, bright.

Discussion

Distribution and endemism - Based on herbarium specimens, Carapa akuri is restricted to central Guyana, in an area already recognized as rich in narrowly endemic species (Kelloff& Funk, 2004; Funk et al., 2007) such as Dicymbe alstonii Sandwith, Chlorocardium rodiei (R. H. Schomb.) Rohwer, H. G. Rieht. & van der Werff, Vouacapoua macropetala Sandwith, Eschweilera potaroensis Sandwith and Swartzia leiocalycina Benth. (ter Steege, 2000). Within this known distribution range, C. akuri is not an abundant species and the extent of its occurrence is estimated to 4143.18 Km^2. Reports of the occurrence of Carapa guianensis in Guyana must now be considered with caution because of the possiblity of misidentification, Two of us (PMF and RST) surveyed crabwood population in forests at the Iwokrama Rainforest Reserve, Forest Ecological Reserve Mabura Hill, and Tropendos Pibri Reserve. Only C. akuri has been identified in all three forests. Inventory data from the Pibiri forest (5 º01'652 N; 58º37'696' W; unpublished report, Tropenbos Guyana Programme, Guyana; van der Hout, 1996) and the Upper Essequibo Conservation Concession (UECC) ( approximatley 3º 41' N' 58º20'W; Welch, 2002) showed densisties of 6 to 13 trees (DBH>10 cm) per hectare.

The ratio of 5 -to 4-merous flowers ranged from (0-)70-100 % for a large sample (N= 50-100 per tree) collected from the ground under isolated trees (with no crown overlap) along trails. At the Turtle Mountain trail (4° 43'57"N, 58°42'45"W), north of the Iwokar- ama field station along the Essequibo river, for instance, trees might have only 4-or 5- merous, or both 4-and 5-merous forms. Alternatively, at the Malali Hill trail (4° 37'48.7"N, 58°39'43.9"W), several kilometres south of the above mentioned C. akuri population, we only observed trees with 5- merous flowers. Thus, an apparent trend was observed for C akuri to occur as 4-merous flowered trees in aggregated populations in swampy, mono-dominant forest with a high density of Mora excelsa Benth., Eperua falcata Aubl. or Pentaclethra macroloba (Willd.) Kuntze. Alternatively, trees with merous flowers were spaced apart on well- drained, hilly terrain, associated with Dicor- ynia guianensis Amshoff and other species in mixed species-rich forests. Additional molecular studies and repeated collection within the Iwokrama Reserve are therefore needed to clarify this spatial diversity, at both local and regional scales. Two leaf characters distinguish the two 5- merous species in the Guiana region. When dried, the leaflets are conspicuously discolor- ous, tan above and brown beneath in Carapa surinamensis, including the type specimen, while they are dry green olive in C. akuri. The most constant vegetative character is the tertiary venation that is dense and raised in C. surinamensis, and loose and diffuse in C. akuri. Also, the seeds of C. akuri are generally larger than those of C. surinamensis. Regarding seed morphological traits, the first axis of PCA (Fig. 4) accounted for 61% of the total variation and had highest positive loadings for SL and SW, and highest negative loadings for the three ratios. The second axis accounted for 24% of the variation, again with SL positively correlated and ST negatively correlated. In the plane of these two first axes (Fig. 4), the seeds of the two species form a continuum but are not intermixed.

Phenology. - Carapa akuri as well as C. surinamensis flower annually during the dry season between November and February (Thomas, 1999, 2002; Forget, 1996). Fruiting occurs in the rainy season, between February and July at the community-level fruiting peak, and toward its end (Forget, 1996; RST and PMF, pers. obs.). Casual fruiting may occur in November suggesting that a second peak of flowering, though weaker in intensity, may be observed during the wet season. The documented minimum tree size to set fruits is 16 cm dbh at Iwokrama forest (Payne, 2001). Seeds of C. akuri are among the largest found in Guianan rainforests (identified as C. procera in Hammond & Brown, 1995).