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Combretum imberbe Wawra

Protologue
Kaiserl. Akad. Wiss. Wien, Math.-Naturwiss. Kl., Anz. 38: 556 (1860).
Family
Combretaceae
Vernacular names
Leadwood (En).
Origin and geographic distribution
Combretum imberbe occurs from southern Tanzania south to northern Namibia, Botswana, Zimbabwe, Mozambique and northern South Africa.
Uses
The wood is used for fence poles, mine props, railway sleepers, mortars, walking sticks, inlay work, toys and turnery. Because of its durability, it is commonly used for the main supporting poles of huts. It is popular for sculpture and lathe work, whereas it is also used to make heavy, extremely durable furniture. The wood is favoured for use as firewood and for charcoal production; it burns slowly and with great heat. The ash from the wood has a high lime content, and is sometimes used as toothpaste and as a substitute of whitewash to decorate walls of houses.
Several plant parts are used in traditional medicine. Powdered roots or leaves and decoctions from roots and leaves are taken to treat diarrhoea. On the other hand, a leaf decoction is applied as an enema to treat constipation. A root infusion is drunk to treat schistosomiasis. Bark powder is applied externally against leprosy. Tea made from the roots or leaves is drunk to treat coughs and colds, and the smoke of burnt leaves is inhaled for the same purposes. A leaf decoction is drunk to relieve chest pain. A root maceration is taken to treat stomach-ache. The roots are used to treat infertility in women. The tree yields an edible gum. The bark has been used for tanning leather. The foliage is eaten by livestock, although it reportedly contains only 4% protein. The tree is claimed to have protective power, and several plant parts are used in ritual ceremonies. Combretum imberbe is useful as an ornamental shade tree.
Production and international trade
In southern Africa Combretum imberbe is in high demand in the carving industry, together with Berchemia spp., Olea europaea L. subsp. cuspidata (Wall. ex G.Don) Cif. and Spirostachys africana Sond. In Mozambique the wood is classified as first class for carving. In Tanzania it has replaced the wood of Bobgunnia madagascariensis (Desv.) J.H.Kirkbr. & Wiersema. In 2003 the official harvest was 3900 m³ of logs, but then a nation-wide ban on the harvest was declared.
Properties
The heartwood is dark brown and distinctly demarcated from the thin, yellow-brown sapwood. The grain is straight, texture fine. The wood is very heavy, with a density of about 1200 kg/m³ at 12% moisture content. It is difficult to work, rapidly blunting cutting edges, but it takes a very nice lustrous polish. The turning properties are excellent. The wood is very durable, even in contact with the ground.
Acetone and ethyl acetate extracts of the leaves of Combretum imberbe showed pronounced anti-inflammatory activity in the cyclooxygenase-1 bioassay, whereas an aqueous extract showed activity against Schistosoma haematobium. The pentacyclic triterpene imberbic acid has been isolated from the leaves; this compound showed potent antibacterial activity against Mycobacterium fortuitum and Staphylococcus aureus. Another pentacyclic triterpene isolated from the leaves, 1α,23-dihydroxy-12-oleanen-29-oic acid-3β-O-2,4-di-acetyl-L-rhamnopyranoside, showed strong antibacterial activity against Staphylococcus aureus and Escherichia coli, as well as strong inhibition of 3α-hydroxysteroid dehydrogenase and moderate cytotoxic activity against some human cancer cell lines. In tests the wood ash showed good results in managing cowpea weevils in stored cowpea seeds.
Adulterations and substitutes
In South Africa the wood of Combretum imberbe is commonly used to supplement the wood of Colophospermum mopane (Benth.) J.Léonard as the main constituent of palisade fences.
Description
Deciduous shrub or small to medium-sized tree up to 20(–30) m tall; bole commonly crooked, up to 100 cm in diameter; bark surface whitish to pale grey or dark grey, with deep longitudinal furrows and irregular transverse cracks; crown spreading, rounded and rather open; twigs glabrous, sometimes spiny at tip. Leaves opposite, simple and entire; stipules absent; petiole up to 1 cm long; blade elliptical to oblong-elliptical or elliptical-obovate, 2.5–8.5 cm × 1–3 cm, cuneate to rounded at base, rounded to obtuse at apex, often with short point, papery to slightly leathery, densely silvery scaly, pinnately veined with 3–7 pairs of lateral veins. Inflorescence an axillary or terminal spike up to 5(–10) cm long; main axis scaly. Flowers bisexual, regular, 4-merous, yellowish, densely scaly, scented, sessile; receptacle consisting of 2 parts, lower part c. 2.5 mm long, upper part indistinct, nearly flat; sepals ovate-triangular, c. 1.5 mm long; petals free, obovate to spatulate, c. 1 mm long, glabrous; stamens 8, free, c. 2 mm long; ovary inferior, 1-celled, style c. 2 mm long, densely glandular at base. Fruit a 4-winged nut, broadly ovoid to nearly orbicular in outline, 1.5–2 cm long, with 2–3 mm long stipe and c. 7 mm broad wings, pale yellowish green, silvery scaly, indehiscent, 1-seeded. Seedling with hypogeal germination, with stalked, nearly orbicular cotyledons.
Other botanical information
Combretum is a very large genus, comprising about 250 species and distributed worldwide in the tropics and subtropics. About 140 species occur in tropical Africa.
Anatomy
Growth rings: (1: growth ring boundaries distinct); (2: growth ring boundaries indistinct or absent). Vessels: 5: wood diffuse-porous; (7: vessels in diagonal and/or radial pattern); (9: vessels exclusively solitary (90% or more)); 13: simple perforation plates; 22: intervessel pits alternate; (23: shape of alternate pits polygonal); 25: intervessel pits small (4–7 μm); 26: intervessel pits medium (7–10 μm); 29: vestured pits; 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 42: mean tangential diameter of vessel lumina 100–200 μm; (45: vessels of two distinct diameter classes, wood not ring-porous); 46: 5 vessels per square millimetre; 58: gums and other deposits in heartwood vessels. Tracheids and fibres: 60: vascular/vasicentric tracheids present; 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 69: fibres thin- to thick-walled. Axial parenchyma: (76: axial parenchyma diffuse); (79: axial parenchyma vasicentric); 80: axial parenchyma aliform; 81: axial parenchyma lozenge-aliform; (89: axial parenchyma in marginal or in seemingly marginal bands); (92: four (3–4) cells per parenchyma strand); 93: eight (5–8) cells per parenchyma strand. Rays: 97: ray width 1–3 cells; 109: rays with procumbent, square and upright cells mixed throughout the ray; 115: 4–12 rays per mm; (116: 12 rays per mm). Mineral inclusions: 136: prismatic crystals present; 137: prismatic crystals in upright and/or square ray cells; (138: prismatic crystals in procumbent ray cells); (141: prismatic crystals in non-chambered axial parenchyma cells).
(P. Détienne & P. Baas)
Growth and development
Combretum imberbe trees grow very slowly. Under natural conditions, mean annual diameter increment rates of only 0.3 mm to 2 mm have been recorded, but under optimal conditions in cultivation young trees may reach 6 m tall in 15 years. Combretum imberbe flowers from November to March, and fruits ripen from February to August. The fruits are dispersed by wind, up to a distance of 50 m from the parent tree.
Combretum imberbe trees can become very old. Radiocarbon dating showed that some specimens were over 1000 years old. Dead trees can remain upright for as much as 80 years.
Ecology
Combretum imberbe occurs in open woodland and wooded savanna, on a wide variety of soils from sandy soils to limestone outcrops, also on alluvial soils and black cotton soils, but only occasionally on heavy clay soils, from sea-level up to 1000 m altitude. It is most common along rivers. Combretum imberbe has an important ecological value for animal species, e.g. as fodder for desert elephants in Namibia and as nesting site for Ruppell’s parrot and hornbills.
Propagation and planting
One kg contains about 11,500 fruits, with the seed accounting for about 45% of the fruit weight. Seeds should be sown while still fresh. They should be soaked in water for a few hours before being pressed into seedling trays filled with river sand. After they have been covered with a thin layer of sand, the seeds should be kept moist. They germinate in 1–2 weeks, but very low germination rates have been recorded (3–5%), as well as high mortality among seedlings. The seedlings can be transplanted into nursery bags after development of the second leaf.
Management
The trees can be managed by coppicing. The number of shoots produced from cut stems is negatively correlated with the height at which the trees are cut, but shorter shoots are produced when the tree is cut close to the ground. A cutting height of 1 m appears most advantageous. In South Africa the majority (nearly 80%) of the Combretum imberbe trees has bole diameters of less than 20 cm. In Tanzania the minimum diameter limit for harvesting has been fixed at 24 cm.
Diseases and pests
Seeds seem to be liable to attacks by insects and rodents. Seedlings are apparently often destroyed by large herbivores such as antelopes and elephants.
Harvesting
Good equipment with hardened and sharp cutting edges is needed to fell the trees and to saw and work the wood.
Genetic resources
Combretum imberbe is widespread and at least locally common. It is therefore not easily liable to genetic erosion. However, studies in Malawi have shown that the wood is in high demand for charcoal production, and that many trees are felled for this purpose. In South Africa Combretum imberbe trees of over 20 cm in bole diameter are selectively felled on a large scale for their timber, whereas smaller-sized trees are commonly cut for firewood. The extent of exploitation appears to be unsustainable in many regions with high human population pressure within the distribution area of the species.
Prospects
There is a lack of knowledge on natural regeneration of Combretum imberbe and on threats to young trees, and the response of Combretum imberbe to harvesting pressure under different environmental and anthropogenic influences is poorly understood. Research on these aspects is needed to develop models for sustainable exploitation. Protection of this slow-growing tree is becoming important, but is certainly worthwhile considering its many services to humans and animals.
Major references
• Angeh, J.E., Huang, X., Sattler, I., Swan, G.E., Dahse, H., Haertl, A. & Eloff, J.N., 2007. Antimicrobial and anti-inflammatory activity of four known and one new triterpenoid from Combretum imberbe (Combretaceae). Journal of Ethnopharmacology 110(1): 56–60.
• Exell, A.W., 1978. Combretaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 4. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 100–183.
• Herrmann, E., Milton, S. & Seymour, C., 2003. A collation and overview of research information on Combretum imberbe Warwa (Combretaceae) and identification of relevant research gaps to inform protection of the species. Department of Water Affairs and Forestry. South Africa, Contract No 2003/089. 23 pp. [Internet]. http://www2.dwaf.gov.za/ dwaf/cmsdocs/Elsa/Docs/PT/ Combretum%20Imberbe%20Report%202003.pdf. Accessed June 2008.
• Mtsweni, P., 2006. Combretum imberbe. [Internet] South African National Biodiversity Institute, Cape Town, South Africa. http://www.plantzafrica.com/ plantcd/combretimb.htm Accessed June 2008.
• Palmer, E. & Pitman, N., 1972–1974. Trees of southern Africa, covering all known indigenous species in the Republic of South Africa, South-West Africa, Botswana, Lesotho and Swaziland. 3 volumes. Balkema, Cape Town, South Africa. 2235 pp.
• Van den Eynden, V., Vernemmen, P. & Van Damme, P., 1992. The ethnobotany of the Topnaar. University of Gent, Belgium. 145 pp.
• van Wyk, B.E. & Gericke, N., 2000. People’s plants: a guide to useful plants of southern Africa. Briza Publications, Pretoria, South Africa. 351 pp.
• Vogel, J.C. & Fuls, A., 2005. The life-span of leadwood trees. South African Journal of Science 101(1/2): 98–100.
Other references
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Gelfand, M., Mavi, S., Drummond, R.B. & Ndemera, B., 1985. The traditional medical practitioner in Zimbabwe: his principles of practice and pharmacopoeia. Mambo Press, Gweru, Zimbabwe. 411 pp.
• Javaid, I. & Ramatlakapela, K., 1995. The management of cowpea weevils (Callosobruchus maculates (Fabricius)) in cowpea seeds by using ash and sand. Journal of Sustainable Agriculture 7: 147–154.
• Katerere, D.R., Gray, A.I., Nash, R.J. & Waigh, R.D., 2003. Antimicrobial activity of pentacyclic triterpenes isolated from African Combretaceae. Phytochemistry 63(1): 81–88.
• McGaw, L.J., Rabe, T., Sparg, S.G., Jäger, A.K., Eloff, J.N. & van Staden, J., 2001. An investigation on the biological activity of Combretum species. Journal of Ethnopharmacology 75: 45–50.
• Milledge, S.A.H, Gelvas, I.K. & Ahrends, A., 2007. Forestry, governance and national development: lessons learned from a logging boom in southern Tanzania. TRAFFIC East/Southern Africa / Tanzania Development Partners Group / Ministry of Natural Resources and Tourism, Dar es Salaam, Tanzania. 252 pp.
• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.
• Steenkamp, V., 2003. Traditional herbal remedies used by South African women for gynaecological complaints. Journal of Ethnopharmacology 86: 97–108.
• Wickens, G.E., 1973. Combretaceae. In: Polhill, R.M. (Editor). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 99 pp.
• Williamson, J., 1955. Useful plants of Nyasaland. The Government Printer, Zomba, Nyasaland. 168 pp.
Sources of illustration
• Coates Palgrave, K., 1983. Trees of southern Africa. 2nd Edition. Struik Publishers, Cape Town, South Africa. 959 pp.
• Exell, A.W., 1978. Combretaceae. In: Launert, E. (Editor). Flora Zambesiaca. Volume 4. Flora Zambesiaca Managing Committee, London, United Kingdom. pp. 100–183.
• van Wyk, P., 1972–1974. Trees of the Kruger National Park. 2 volumes. Purnell, Cape Town, South Africa. 597 pp.
Author(s)
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands


Editors
R.H.M.J. Lemmens
PROTA Network Office Europe, Wageningen University, P.O. Box 341, 6700 AH Wageningen, Netherlands
D. Louppe
CIRAD, Département Environnements et Sociétés, Cirad es-dir, Campus international de Baillarguet, TA C-DIR / B (Bât. C, Bur. 113), 34398 Montpellier Cedex 5, France
A.A. Oteng-Amoako
Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article:
Lemmens, R.H.M.J., 2009. Combretum imberbe Wawra. 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.

















































Distribution Map wild


1, tree habit; 2, part of leafy twig; 3, flower in longitudinal section; 4, fruit.
Redrawn and adapted by Iskak Syamsudin