Prota 7(1): Timbers/Bois d’œuvre 1
Bot. Jahrb. Syst. 15: 135 (1892).
Sterculiaceae (APG: Malvaceae)
Egyptian plane tree, large-leaved star chestnut, large-leaved sterculia (En). Mbalamwezi, mkwera nyani, mukungu, mukulamishi, mulende (Sw).
Origin and geographic distribution
Sterculia quinqueloba occurs from eastern DR Congo, Burundi and Tanzania south to Zambia, Namibia, Zimbabwe and Mozambique.
The wood of Sterculia quinqueloba is used in Zambia for furniture and mine props. In Malawi it is used for coffins and light construction. It is also suitable for flooring, interior trim, joinery, turnery, poles, veneer, plywood and pulpwood. It is also used as fuelwood and for making charcoal.
The seeds are edible. Trees are tapped for the gum, which is traded as ‘gum karaya’ together with the gum of other Sterculia spp. and used as thickener, emulsifier, laxative and denture adhesive. The bark is used to make floormats and yields fibres that are used to make ropes, mats and sacks. Sterculia quinqueloba is planted as an ornamental and roadside tree.
A decoction of leaves and bark of thin branches is drunk to cure stomach-ache. A decoction of the bark from branches is recorded to be given as enema as remedy for diarrhoea, whereas boiled bark is reportedly used as enema against constipation. A decoction of leaves and roots is drunk to cure malaria.
Production and international trade
In Tanzania Sterculia quinqueloba is classified as a lower value timber species. It is unknown if any of its timber or gum is traded in the international market.
The heartwood is pinkish red when freshly cut, darkening to mid-brown on exposure, and distinctly demarcated from the pale yellow, up to 6 cm wide sapwood. The grain is straight, texture medium to coarse. The numerous very broad rays visible on tangential surfaces give a speckled effect.
The wood is moderately heavy, with a density of 690–880 kg/m³ at 12% moisture content. Air drying is very slow and must be done carefully to avoid surface checking, splitting, cupping and collapse. Boards 2.5 cm thick need 6 months to air dry to 18% moisture content and 2 months more to 14% moisture content. Boards 5 cm thick need 14 months to air dry to 25% moisture content, and further drying progresses only at a rate of 1% moisture content per month. Kiln drying is very difficult or impossible. The rates of shrinkage from green to oven dry are about 3.0% radial and 7.0% tangential. Once dried, the wood is moderately stable in service.
The strength of the wood is rather low. At 12% moisture content, the modulus of rupture is 71–75 N/mm², modulus of elasticity 9500–10,200 N/mm², compression parallel to grain 40–42 N/mm², shear 9–11.5 N/mm², cleavage 60 N/mm radial and 59 N/mm tangential, and Janka side hardness 5960 N.
The wood saws easily and power demand is low. Planing and moulding are easy. The wood finishes to a good polish, and it bores and drills fairly well. Nailing properties are poor; the wood tends to split and pre-boring is recommended.
The wood is moderately durable to durable, being moderately resistant to termites. The sapwood is susceptible to Lyctus borers. The heartwood is extremely resistant to impregnation with preservatives, the sapwood is permeable.
Carefully harvested and graded gum meets the requirements of commercial ‘gum karaya’ (normally derived from the Indian species Sterculia urens Roxb. and having the European code E 416): a maximum of 200 g/kg moisture content and 30 g/kg of insoluble matter; it also has low levels of aluminium, manganese and cobalt. The high tannin content of the gum of Sterculia quinqueloba, however, limits its usefulness in foods and pharmaceuticals. The gum of Sterculia quinqueloba possesses solubility and viscosity properties similar to commercial gum arabic from Acacia spp., especially in having a rather low viscosity which is similar in hot and cold water. However, Sterculia quinqueloba gum does not meet all specifications required of gum arabic and much higher amounts of the gum are needed to obtain similar results.
Deciduous small to medium-sized tree, up to 20(–40) m tall; bole branchless for up to 4.5 m or more, up to 100 cm in diameter, usually straight and cylindrical; bark surface grey to pale greenish brown, smooth, flaking, inner bark mottled red and fibrous; young twigs with triangular bud-scales. Leaves alternate, simple; stipules early caducous; petiole 6–18 cm long; blade orbicular in outline, 8–36 cm × 10–34 cm, with 5 triangular, acuminate lobes, deeply cordate at base, soft hairy with stellate hairs on lower surface. Inflorescence an axillary, narrow panicle 15–35 cm × 6–11 cm, sticky hairy; bracts 3–7 mm long, caducous. Flowers unisexual, regular, 5-merous, pale or yellowish green, c. 3.5 mm long; perianth campanulate with lobes c. 1 mm × 1 mm, outside sticky hairy; male flowers with 8–10 anthers borne on a common stalk c. 1.5 mm long; female flowers with ovary consisting of 5 carpels united loosely. Fruit usually consisting of 5 woody follicles 5–8 cm × 1–1.5 cm, densely soft hairy, yellow-brown, sticky, many-seeded. Seeds ellipsoid, 7 mm × 4–7 mm, grey-black, glabrous.
Sterculia quinqueloba flowers when leaves are present.
Sterculia comprises about 150 species and occurs throughout the tropics. In tropical Africa about 25 species can be found. Sterculia quinqueloba is often confused with Sterculia appendiculata K.Schum. The latter species has a smooth, non-flaking bark, occurs in more humid regions, and is found at altitudes up to 750 m. The differences in flowers and fruits between the 2 species are distinct.
Sterculia quinqueloba is found in dry, deciduous woodland, often on termite-mounds, rocky outcrops and hills, usually in association with Brachystegia and Isoberlinia spp., up to 1650 m altitude.
Propagation of Sterculia quinqueloba can be done by sowing and with cuttings or truncheons. Seeds can be tested after collection by submersion in water; those that float are usually damaged by insects and should be discarded. Seeds should be dried to 9–12% moisture content before storage. At a storage temperature of 4°C a germination rate of 70% can be maintained for half a year. Sterculia quinqueloba tolerates pruning and can be coppiced. Star shakes may develop in storage to the full width of the log.
Genetic resources and breeding
Sterculia quinqueloba is considered not to be at risk of genetic erosion because it is widespread and tolerating a range of habitats. However, recent reports indicate that wherever exploitation of species with timber of high quality has led to their eradication, trade shifts to Sterculia quinqueloba timber, resulting in population densities dropping sharply.
Monitoring the utilization of Sterculia quinqueloba could reveal threats for the species and may indicate potential for sustainable exploitation. The potential for production of gum needs to be evaluated.
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Correct citation of this article:
Bosch, C.H. & Louppe, D., 2008. Sterculia quinqueloba (Garcke) K.Schum. In: Louppe, D., Oteng-Amoako, A.A. & Brink, M. (Editors). Prota 7(1): Timbers/Bois d’œuvre 1. [CD-Rom]. PROTA, Wageningen, Netherlands.
obtained from Zimbabweflora
obtained from Zimbabweflora
obtained from Zimbabweflora