Prota 7(2): Timbers/Bois d’œuvre 2
Prodr. 3: 13 (1828).
Silver terminalia (En).
Origin and geographic distribution
Terminalia sericea occurs from southern DR Congo and Tanzania south to Namibia, northern South Africa and Swaziland.
The tree boles of Terminalia sericea are highly valued as poles for the construction of houses and huts, e.g. in south-western Zambia and KwaZulu-Natal province in South Africa. They are said to last for at least 5 years, and are also considered valuable for fencing. The wood is used for furniture, tool handles, bows, beehives and ox yokes. It is suitable for flooring, joinery, interior trim, ship building, vehicle bodies, mine props, sporting goods, agricultural implements, railway sleepers and turnery. It is popular as firewood and for charcoal production.
The bark is used as rope, often to tie together poles for huts, and it provides a yellow dye and tannin, whereas the leaves are used as mordant in dye bathes. The flexible roots are used as cross-laths in huts. Root extracts or infusions are used in traditional medicine to treat venereal diseases, diarrhoea, dysentery, colic, pneumonia, cough, skin diseases, schistosomiasis, gonorrhoea and problems with menstruation, and applied as an eye wash to treat trachoma and ophthalmia. Pulverized bark is applied to wounds and taken to treat diabetes. Leaf extracts serve to treat diarrhoea and stomach complaints, and a leaf infusion to treat cough. Pulverized leaves are applied as a dressing to wounds. The twig juice, leaves and roots are used in Namibia and Botswana in mixtures with other plants and larvae of beetles to prepare arrow poison. The tree produces a gum that is eaten by local people. In the rainy season edible caterpillars commonly feed on the leaves. The flowers provide nectar for honey bees, whereas the leaf hairs have been used for glazing pottery. The leaves are browsed by cattle; Terminalia sericea contributes significantly to cattle diet during the hot and dry season in the northern Kalahari desert. The tree has ecological values as soil improver and for erosion control. It is locally regarded as sacred.
The heartwood is dull yellow with brownish stripes, darkening with age, and distinctly demarcated from the narrow sapwood. The grain is usually straight, occasionally interlocked, texture moderately coarse and uneven.
The wood is heavy, with a density of 840–920 kg/m³ at 12% moisture content. It air dries fairly rapidly, with moderate checking and distortion. The rates of shrinkage are moderate, from green to oven dry 3.8% radial and 6.4% tangential. At 12% moisture content, the modulus of rupture is 91 N/mm², modulus of elasticity 11,760 N/mm², compression parallel to grain 58 N/mm², shear 10.5 N/mm², Janka side hardness 9200 N and Janka end hardness 11,065 N.
The wood works well with both hand and machine tools. It planes and finishes easily, although rather dull surfaces are produced. The heartwood is fairly durable, but the sapwood is susceptible to Lyctus attack. The wood is resistant to impregnation by preservatives. The sawdust may cause inflammations of the respiratory organs and skin.
The pentacyclic triterpenoid sericic acid has been isolated from the roots, as well as its glycoside sericoside. Root extracts and sericic acid have anti-inflammatory and wound-healing properties, and showed antibacterial and antifungal activities. Root extracts are particularly active against the bacteria Staphylococcus aureus and Streptococcus pyogenes and against the fungi Candida albicans, Candida glabrata and Cryptococcus neoformans. Sericoside has anti-inflammatory activity, whereas strong lipolytic activity has also been suggested. Anolignan B is another bioactive compound isolated from the roots. It showed activity against both gram-positive and gram-negative bacteria, as well as anti-inflammatory activity. The results from tests support the ethnomedical use of the roots. However, caution is needed because in Tanzania several cases of death after application of root extracts have been recorded. In tests root extracts were toxic to brine shrimps. Root extracts showed strong cytotoxic effects against several human cancer cell lines. Methanol extracts of the leaves showed strong in-vitro activity against HIV-1 reverse transcriptase.
The nutritive value of Terminalia sericea leaves is rather low, with a crude protein content of about 11.5%; the tannin content of the leaves is low.
Deciduous shrub or small to medium-sized tree up to 16(–23) m tall; bole branchless for up to 8 m, straight or crooked, up to 50(–100) cm in diameter; bark surface cream-coloured to grey-brown, deeply grooved; crown layered, with horizontal branches; branchlets red-brown to purplish, with peeling bark, silky hairy when young. Leaves arranged spirally, clustered near ends of branchlets, simple and entire; stipules absent; petiole up to 1.5 cm long; blade narrowly elliptical-obovate, 5–13 cm × 1–4.5 cm, cuneate at base, rounded to short-acuminate at apex, silvery silky hairy especially when young, pinnately veined with 5–8(–13) pairs of indistinct lateral veins. Inflorescence an axillary spike 5–12 cm long, densely silky hairy; peduncle 2.5–5 cm long. Flowers bisexual or male, regular, 4–5-merous, greenish white; receptacle spindle-shaped, c. 5 mm long; sepals triangular, c. 2 mm long; petals absent; stamens usually 10, free, c. 4 mm long; disk annular, hairy; ovary inferior, 1-celled, style 3–5 mm long. Fruit a winged nut, broadly elliptical in outline, 3–4 cm × 1.5–2.5 cm including the wing, stipe up to 0.5 cm long, pinkish or purplish brown, finely hairy, indehiscent, 1-seeded.
Terminalia sericea grows slowly. Annual elongation of the bole results in a layered crown. Flowers develop together with young leaves, usually in September–November. The flowers have a strong and unpleasant smell, and are probably pollinated by flies. Fruits ripen 3–5 months after flowering, but they may remain on the tree for up to 1 year.
Terminalia is a pantropical genus of about 200 species. In tropical mainland Africa about 30 species occur naturally, in Madagascar about 35. It has been suggested that Terminalia sericea may hybridize with Terminalia kaiserana F.Hoffm. and Terminalia trichopoda Diels. In some regions intermediate specimens are fairly common.
The wood of Terminalia prunioides C.Lawson is used for similar purposes as that of Terminalia sericea: for building huts, houses and ships, and for implement handles. It is very heavy, with a density of about 1100 kg/m³ at 12% moisture content, and very hard and exceptionally durable. It is also used as firewood. In southern Africa the bark is chewed to treat cough, sore throat and stomach-ache, the roots are chewed to treat colds and a root decoction is taken to treat constipation, cough and colds. Terminalia prunioides is a shrub or small tree up to 15 m tall occurring in open woodland from Somalia south to Namibia, Mozambique and northern South Africa. The boles of Terminalia stuhlmannii Engl., a small tree up to 12 m tall occurring in woodland and wooded grassland from Tanzania south to Botswana, Zimbabwe and Mozambique, are also used for hut building.
Terminalia sericea occurs in open woodland and wooded grassland, often together with Brachystegia spp., at 450–1300 m altitude in areas with moderate rainfall. It is often common along wetlands, sometimes forming almost pure stands, and may be dominant in woodland degraded by fire. It seems to prefer sandy and deep, well-drained soils, and can grow on very poor soils that are generally not suitable for agriculture.
It is recommended to remove the wing of the fruit before sowing. The bole is often crooked, but lopping may result in straight boles. The preferred length of the poles used for house building in Zambia is 2.5–3 m. In KwaZulu-Natal province in South Africa, the mean diameter of poles used as main posts in houses is 6 cm and the mean length 2.2 m, and when used as roof laths 4 cm and 2.6 m, respectively. In Zambia the bark is removed and the poles are soaked in water for a few weeks, which reputedly increases the durability. The trees can be coppiced, and harvest intervals for fuelwood poles have been recommended as 4–9 years.
In the rainy season the leaves are commonly attacked by large numbers of caterpillars. The twigs often have galls. The fruits may be deformed by parasites, becoming slender, twisted and hairy.
Genetic resources and breeding
Terminalia sericea is widespread and in many regions common, and not liable to genetic erosion. On the contrary, it is often regarded as a major encroaching species, which has adverse effects on cattle production because it prevents the growth of grass.
Although Terminalia sericea is usually of too small size and grows too slowly to be of value to the international timber market, it is certainly important for wood production for local application, especially for building houses. The presence of anti-inflammatory and wound-healing compounds in the roots deserves more attention. Sericoside has already been tested in topical emulsion based formulations with promising results. In addition to the uses of the wood and in local medicine, Terminalia sericea is important for forage supply in the dry season, firewood production and soil protection, making it a true multipurpose species that deserves more research attention.
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Correct citation of this article:
Lemmens, R.H.M.J., 2009. Terminalia sericea Burch. ex DC. 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.