Prota 7(2): Timbers/Bois d’œuvre 2
Mem. Mus. natl. Hist. nat., Paris n.s. 18: 260 (1944).
Origin and geographic distribution
Protorhus ditimena is endemic to northern and eastern Madagascar.
The wood of Protorhus ditimena and other Protorhus spp., known as ‘ditimena’, is used in Madagascar for construction, joinery, flooring, panelling, moulding and railway sleepers. The leaves are used in traditional medicine as sedative.
The heartwood is chestnut brown and streaked; it is distinctly demarcated from the paler, up to 6 cm wide sapwood. The grain is generally straight, texture fine. The wood is moderately heavy, with a density of 750–810 kg/m³ at 12% moisture content. It air dries easily with little checking and warping. The rates of shrinkage during drying are medium, from green to oven dry 3.4–4.6% radial and 9.1–10.3% tangential. At 12% moisture content, the modulus of rupture is 156–177 N/mm², modulus of elasticity 11, 800–14,400 N/mm², compression parallel to grain 58–70 N/mm², shear 7.5–8.5 N/mm², cleavage 21–25 N/mm and Chalais-Meudon side hardness 5.8. The wood works easily, glues satisfactorily and the nailing properties are moderate. The wood is moderately durable, with fair resistance to termites, but it is rather susceptible to fungal attacks. Impregnation with preservatives under pressure showed fairly good results. For usage as railway sleepers, it is advised to treat the wood with preservatives under pressure.
Evergreen, small to medium-sized tree up to 25 m tall; bole up to 35 cm in diameter; bark surface slightly rough, finely flaky, blackish, inner bark reddish, exuding a whitish resin; young twigs yellowish brown short-hairy. Leaves opposite to alternate, simple and entire; stipules absent; petiole 5–12 mm long; blade obovate to elliptical, 2–7.5 cm × 2–3 cm, cuneate to obtuse at base, rounded to notched at apex, leathery, brownish green above and reddish below, glabrous, pinnately veined with 15–25 lateral veins. Inflorescence an axillary short panicle, densely reddish brown short-hairy, densely flowered. Flowers unisexual, regular, 4–5-merous, whitish or yellowish, sessile; calyx lobes rounded, c. 1 mm long; petals free, ovate, 2–3 mm long, densely short-hairy; stamens c. 2 mm long; disk slightly lobed, hairy; ovary superior, hairy, 3-celled, style short, 3-branched; male flowers with rudimentary ovary, female flowers slightly larger than male ones and with rudimentary stamens. Fruit an ovoid to oblong drupe up to 3 cm long, slightly grooved, reddish brown short-hairy, with resinous pulp, 1-seeded.
Protorhus ditimena grows slowly. Trees flower in September–December and fruits mature 2–3 months later. The fruits are eaten by birds, which probably serve as seed dispersers.
Protorhus comprises nearly 20 species, all endemic to Madagascar except Protorhus longifolia (Bernh.) Engl., which is from South Africa. It has been proposed to transfer the species from Madagascar to a separate genus Abrahamia. Micronychia, an endemic genus from Madagascar, is closely related to Protorhus, but differs in sigmoid, mango-like fruits.
The wood of several other Protorhus spp. is used for similar purposes as that of Protorhus ditimena. One of these is Protorhus grandidieri Engl., a small to medium-sized tree up to 25 m tall from western Madagascar. The gum-resin, bark and leaves are used in traditional medicine, but no details are available. The wood of Protorhus sericea Engl., Protorhus louvelii H.Perrier and Protorhus thouvenotii Lecomte, all occurring in eastern Madagascar, is similar in properties and uses to that of Protorhus ditimena. A leaf infusion of Protorhus sericea is administered to treat indigestion. The leaves are also valued in traditional medicine to treat heart complaints and as disinfectant.
Protorhus ditimena occurs in evergreen forest up to 1250(–1600) m altitude. It is commonly found along watercourses.
Genetic resources and breeding
Protorhus ditimena is quite widespread, but it occurs scattered in the forest and is limited to threatened types of forest. Therefore, caution is needed in harvesting this species to prevent genetic erosion. This is even more the case in some other Protorhus spp. with limited areas of distribution.
Protorhus ditimena and other Protorhus spp. have been recommended for enrichment planting in natural forest, and as non-pioneer light-demanders that also tolerate some shade they are suited for that purpose. However, they grow slowly and long cutting cycles are needed for timber production, and therefore commercial exploitation on a sustainable basis seems to have little prospects.
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Correct citation of this article:
Lemmens, R.H.M.J., 2009. Protorhus ditimena H.Perrier. In: Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). Prota 7(2): Timbers/Bois d’œuvre 2. [CD-Rom]. PROTA, Wageningen, Netherlands.