Cylicodiscus gabunensis Harms

Cylicodiscus gabunensis (Taub) Harms

Standard trade name: Okan

Local names: Denya (Ghana), Imbeli-deli (Sierra Leone), Boucmon (Ivory Coast), Olosan, Okan, (Nigeria), Adum (Cameroons)

This large tree has a clear bole about 120 ft high and about 10 ft in diameter. Crown somewhat flat, wide-spreading, and fairly open. Buttresses short, slash pale yellow, stringy, giving an offensive smell. Young bark ashy white turning reddish brown or almost black, rough and scaly later. Saplings have brown thorns on the stems. Leaves bipinnate, pinnae 1 pair, opposite, leaflets alternate, ovate, long-pointed, glabrous above, reddish on young seedling trees. Flowers small, numerous, yellowish or greenish white, in slender spike-like and paired racemes up to 6 in long; stamens 10. Fruits up to 3 ft × 1¾ in, yellow at first, turning brown, with irregular longitudinal raised nerves and covered with rusty scales; seeds flat, up to 3 in or more long, thinly winged.

GENERAL DESCRIPTION.—The sapwood, 2–3 in wide, is pinkish and the heartwood is yellow-brown with dark brown or reddish brown streaks. The wood is exceedingly heavy, averaging about 591 lb/ft3 air dry, and about 781 lb/ft3 green (45% MC). The grain is typically interlocked, and the texture moderately coarse.

SEASONING.—Okan seasons slowly with a marked tendency to split and check. British Forest Products Laboratory kiln schedule B is recommended (FPRL, 1956).

DURABILITY.—Okan is rated very durable. The sapwood is susceptible to attack by powder-post beetles (Bostrychidae and Lyctidae). It is extremely resistant to preservative treatment. The sapwood is also resistant.

WORKING QUALITIES.—The timber is very hard and difficult to cut with machine and hand tools and dulls their cutting edges fairly quickly. The pronounced interlocked grain makes it difficult to obtain a clean finish in a number of operations. Okan stains and polishes satisfactorily but requires preboring before nailing.

USES.—It is most suitable for piling and wharf decking as it can be used without preservative treatment. Its resistance to wear is very high and it is recommended for heavy-duty flooring in factories and warehouses. Its density and interlocked grain make it unsuitable for plywood manufacture.

XYLEM ANATOMY.—Growth rings absent. Wood diffuse-porous. Vessels: mostly solitary, occasionally in multiples of 2 or 3, oval in outline; average pore diameter 224μm, range 168μm–322μm; vessel wall thickness 4μm, perforation plate simple; vessel element end wall inclination slightly oblique to transverse; intervascular pitting alternate. Imperforate tracheary elements: fiber tracheids, average length 420μm, range 294μm–630μm. Vascular rays: predominantly biseriate but with few uniseriate, bi-seriate rays 8 to 55 cells high, uniseriate rays 5 to 15 cells high. Axial parenchyma: paratracheal, sometimes vasicentric, conspicuously banded. Tanniniferous material present in some vessels and ray cells.