Prota 11(1): Medicinal plants/Plantes médicinales 1
Bot. Jahrb. Syst. 49: 430 (1913).
Caesalpiniaceae (Leguminosae - Caesalpinioideae).
Stachyothyrsus tessmannii Harms (1910).
Origin and geographic distribution
Pachyelasma tessmannii occurs from southern Nigeria east to the Central African Republic, and south to Gabon and DR Congo.
In Cameroon the fruit of Pachyelasma tessmannii is used to cure diarrhoea and as an abortifacient. For the latter either an extract of the ground fruits is administered as an enema or the macerated fruits are added to water and the patient takes a bath in the solution. In Gabon and DR Congo the fruits, seeds and bark are used as fish poison and the species is reported as one of the most effective fish poisons of Central Africa.
The tree is used for timber to a limited extent. The gigantic dimensions of fully-grown trees make felling and transport hazardous and conversion work difficult with the usual equipment. As a result such giant trees have generally been left standing in commercial timber operations. The timber is known in trade as ‘mekogho’, ‘eyek’ or ‘faux tali’. The wood is suitable for heavy construction, boat building, vehicle bodies, furniture and cabinet work, joinery, sporting goods and implements, interior trim, toys and novelties, and turnery. It is particularly suitable for very thin veneer.
The methanol extract of the root bark of Pachyelasma tessmannii exhibits molluscicidal properties. Four triterpene saponins, pachyelasides A–D, have been isolated from the root bark, and each of them showed molluscicidal properties.
The heartwood is reddish brown and usually distinctly demarcated from the whitish pink sapwood, which is up to 10 cm wide. The heartwood is heavy and hard. The grain is often interlocked or wavy, texture coarse. At 12% moisture content the density is 810–900 kg/m3. The rates of shrinkage are high; quarter-cutting of the logs is recommended. The wood saws well, but strength is required. It is difficult to machine and plane. The use of a filler is required to produce a smooth finish, but a filler is not easily applied. The nailing and screwing properties are good. The wood is durable and only rarely attacked by termites and marine borers, but attack by pinhole borers may occur. The sapwood is moderately resistant to impregnation with preservatives, the heartwood resistant.
The timber of Pachyelasma tessmannii can be confused with that of ‘tali’ (Erythrophleum ivorense A.Chev.).
Very large tree up to 60 m tall; bole straight and cylindrical, up to 250 cm in diameter; with buttresses; bark rough, greyish; crown dome-shaped. Leaves alternate, bipinnately compound with 2–5 pairs of opposite or rarely alternate pinnae, up to 35 cm long; stipules lanceolate-linear, soon falling; petiole 2–7 cm long, rachis 5–15 cm long; leaflets alternate, 9–14 per pinna, oblong to oblong-lanceolate, 4–11 cm × 1.5–3.5 cm, base asymmetrical, cuneate to obtuse, apex obtuse, rounded or notched. Inflorescence an axillary or terminal panicle consisting of spike-like racemes up to 18 cm long. Flowers bisexual, regular, 5-merous, malodorous; pedicel 2–3 mm long; sepals c. 2 mm × 2 mm, yellowish green; petals narrowly obovate, up to 6 mm × 3 mm, cherry-red with yellow base; stamens 10, free, c. 4 mm long; ovary superior, long woolly hairy, 1-celled, style cylindrical, c. 3 mm long. Fruit a linear-oblong or oblong-lanceolate, flattened pod, 15–35 cm × 3–4 cm, sutures thickened, indehiscent, thickly woody, pendulous, black, 10–18-seeded. Seeds ovoid, compressed, c. 20 mm × 9 mm × 6 mm.
Pachyelasma comprises a single species and is closely related to Erythrophleum.
Pachyelasma tessmannii occurs in primary rainforest.
Genetic resources and breeding
Pachyelasma tessmannii is widely distributed and not very sought after for timber. Hence no major threats of genetic erosion are envisaged although large-scale habitat destruction could have a negative impact.
The recent isolation of novel saponins from the root bark of Pachyelasma tessmannii will undoubtedly fuel interest in its pharmacology and as the fruits have the widest application in folk medicine, research should also target the fruits.
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Correct citation of this article:
Bosch, C.H., 2006. Pachyelasma tessmannii (Harms) Harms. In: Schmelzer, G.H. & Gurib-Fakim, A. (Editors). Prota 11(1): Medicinal plants/Plantes médicinales 1. [CD-Rom]. PROTA, Wageningen, Netherlands.