Cynometra alexandri (PROTA)

Plant Resources of Tropical Africa Introduction

List of species

General importance
Geographic coverage Africa
Geographic coverage World
Carbohydrate / starch
Medicinal
Timber
Fuel
Ornamental
Auxiliary plant
Climate change

Cynometra alexandri C.H.Wright

distribution in Africa (wild)

1, base of bole; 2, leafy twig; 3, flowering twig; 4, flower; 5, fruits. Redrawn and adapted by Iskak Syamsudin

wood in transverse section

wood in tangential section

wood in radial section

Protologue: H.H.Johnst., Uganda Prot. 1: 325 (1902).

Family: Caesalpiniaceae (Leguminosae - Caesalpinioideae)

Vernacular names

• Tuna (Sw).

Origin and geographic distribution

Cynometra alexandri occurs from DR Congo east to western Uganda and western Tanzania.

Uses

The wood, traded from Uganda as ‘muhimbi’ or ‘Uganda iron wood’, is used for heavy construction, heavy flooring, ship building, vehicle bodies, mine props, railway sleepers, furniture, cabinet work, sporting goods, toys, novelties, agricultural implements, tool handles, draining boards, carving and turnery. It has a high resistance to abrasion and is very suitable for heavy-duty flooring. The wood is also used as firewood and for charcoal production.

In Uganda Cynometra alexandri is planted to control erosion and occasionally as an ornamental shrub. Flowering trees are a source of pollen for honey bees. The bark serves to make baskets and is also used as an arrow poison. In DR Congo bark powder is applied to wounds. Caterpillars feeding on the leaves are collected in DR Congo to serve as bait for fishing.

Production and international trade

The wood of Cynometra alexandri is used locally and only occasionally traded on the international market, mostly as flooring blocks and strips. Trade statistics are not available. Much Cynometra alexandri timber has been exported in the 1950s and 1960s from western Uganda to Europe.

Properties

The heartwood is pinkish brown, darkening upon exposure to reddish brown with darker streaks. It is distinctly demarcated from the 5–7.5 cm wide, greyish white sapwood which turns pale yellow upon exposure. The grain is usually interlocked, texture fine.

The wood is moderately heavy to heavy, with a density of 760–940 kg/m³ at 12% moisture content. It air dries slowly with only slight distortion, but checking and end splitting may occur. Drying should therefore be done with care, especially kiln drying. The rates of shrinkage are moderate, from green to 12% moisture content about 2.5% radial and 4.5% tangential, and from green to oven dry 4.3% radial and 7.8% tangential. Once dry, the wood is only moderately stable in service.

At 12% moisture content, the modulus of rupture is 109–202 N/mm², modulus of elasticity 10,900–17,500 N/mm², compression parallel to grain 51–72 N/mm², shear 17–23 N/mm², cleavage 22 N/mm, Janka side hardness 11,300–11,830 N, Chalais-Meudon side hardness 5.4 and Janka end hardness 13,160 N.

The wood is difficult to saw and work, and has severe blunting effect on cutting edges and saw teeth; the use of tungsten-tipped cutting edges is recommended. Resin may build up on saw teeth. In planing operations a 15° cutting angle is recommended to obtain a good finish, and cutting edges should be kept sharp. The wood takes a fine polish. Boring and mortising properties are less favourable with a tendency of splitting at exits. Pre-boring is needed for nailing and screwing, but the wood holds nails and screws well. It glues moderately well and can be stained satisfactorily requiring little filling. It turns well. The steam bending properties are moderate. The wood is durable, being resistant to termite and Lyctus attacks, but occasionally liable to pinhole borer and longhorn beetle attacks. It is also durable in water and resistant to marine borers. The heartwood is resistant to impregnation with preservatives, but the sapwood is permeable.

Description

• Evergreen medium-sized to large tree up to 50 m tall; bole branchless for up to 25 m but often shorter, straight and cylindrical or twisted, up to 150(–180) cm in diameter, with large, thin plank buttresses up to 5 m high; bark surface smooth but irregularly flaking, grey to reddish grey or pale brown, inner bark reddish brown; crown flattened with spreading branches; twigs short-hairy but becoming glabrous.
• Leaves arranged spirally, paripinnately compound with 2(–3) pairs of leaflets; stipules linear, 0.5–1 cm long; petiole up to 0.5 cm long, rachis up to 3.5 cm long, widely grooved above; leaflets opposite, sessile, obliquely lanceolate to elliptical or ovate, 1–10 cm × 0.5–4 cm, upper ones largest, acuminate at apex, glabrous.
• Inflorescence an axillary or terminal panicle up to 6 cm long, short-hairy, with densely crowded flowers; bracts small.
• Flowers bisexual, nearly regular, whitish or sometimes pinkish, fragrant; pedicel up to 1.5 cm long, glabrous, jointed near apex and persistent after shedding of flowers; sepals 4(–5), c. 4.5 mm long, reflexed; petals 5, free, obovate-lanceolate, 5–6 mm long; stamens usually 10, free, 6–8 mm long, slightly unequal; ovary superior, c. 2.5 mm long, with stipe c. 2 mm long, hairy, 1-celled, style 3–4 mm long.
• Fruit an obliquely oblong to obovate, flat pod 5–10 cm × 3–5 cm, with 0.5–1 cm long stipe, rounded or short-pointed at apex, smooth and brown, dehiscent with 2 woody, twisting valves, few-seeded.
• Seeds rounded, flat, 1.5–2 cm in diameter, brownish.
• Seedling with epigeal germination; hypocotyl 4–11 cm long, epicotyl 5.5–13 cm long, short-hairy; first 2 leaves opposite, with 4 leaflets, subsequent leaves alternate.

Other botanical information

Cynometra comprises about 90 species and occurs in the tropical regions of the world. Approximately 25 species can be found in mainland tropical Africa and about 10 in Madagascar. Tropical Asia and tropical America have about 25 species each.

Cynometra webberi

Cynometra webberi Baker f. also occurs in East Africa, where it is restricted to coastal dry evergreen forest in south-eastern Kenya and eastern Tanzania. It is a small tree up to 12 m tall with short bole. The pinkish brown, heavy and durable wood is used for heavy construction and furniture. Cynometra webberi is included in the IUCN Red List as vulnerable.

Anatomy

Wood-anatomical description (IAWA hardwood codes):

• Growth rings: 2: growth ring boundaries indistinct or absent.
• Vessels: 5: wood diffuse-porous; 13: simple perforation plates; 22: intervessel pits alternate; 23: shape of alternate pits polygonal; 24: intervessel pits minute (≤ 4 μm); 29: vestured pits; 30: vessel-ray pits with distinct borders; similar to intervessel pits in size and shape throughout the ray cell; 41: mean tangential diameter of vessel lumina 50–100 μm; 47: 5–20 vessels per square millimetre; 48: 20–40 vessels per square millimetre; 58: gums and other deposits in heartwood vessels.
• Tracheids and fibres: 61: fibres with simple to minutely bordered pits; 66: non-septate fibres present; 70: fibres very thick-walled.
• Axial parenchyma: (78: axial parenchyma scanty paratracheal); (79: axial parenchyma vasicentric); 80: axial parenchyma aliform; (81: axial parenchyma lozenge-aliform); (82: axial parenchyma winged-aliform); 83: axial parenchyma confluent; 86: axial parenchyma in narrow bands or lines up to three cells wide; (91: two cells per parenchyma strand); 92: four (3–4) cells per parenchyma strand; 93: eight (5–8) cells per parenchyma strand.
• Rays: 96: rays exclusively uniseriate; 97: ray width 1–3 cells; 104: all ray cells procumbent; (106: body ray cells procumbent with one row of upright and/or square marginal cells); 116: ≥ 12 rays per mm.
• Storied structure: 118: all rays storied; 120: axial parenchyma and/or vessel elements storied; 121: fibres storied.
• Mineral inclusions: 136: prismatic crystals present; 142: prismatic crystals in chambered axial parenchyma cells; (143: prismatic crystals in fibres).

(P. Mugabi, P. Baas & H. Beeckman)

Growth and development

Young plants require shade until they are established. Trees grow slowly. In natural forest in western Uganda, it has been estimated that trees reach a bole diameter of 60 cm after about 80 years.

Older trees have large, widely spreading buttresses and spreading roots, making establishment on shallow soils and slopes more easy. Trees lose their leaves irregularly. In DR Congo they flower in March–May. In the Budongo forest reserve in western Uganda, chimpanzees have a preference for Cynometra alexandri trees to build their nests. The presence of vesicular-arbuscular mycorrhizae has been recorded.

Ecology

Cynometra alexandri occurs in evergreen and semi-deciduous forest at 700–1200(–1400) m altitude. In Budongo forest reserve in western Uganda, where dense stands of Cynometra alexandri occur, the temperature range is 11–30°C, mean temperature 21°C and mean annual rainfall about 1500 mm, with a pronounced dry season in January–February. Forest dominated by Cynometra alexandri is considered a climax vegetation type. Cynometra alexandri is susceptible to forest fires.

Propagation and planting

Natural regeneration of Cynometra alexandri is good in natural forest in western Uganda with different histories of logging and other disturbances. Cynometra alexandri is normally propagated by seeds and wildings. There are about 290 seeds per kg. Seeds are usually collected during the raining season from the ground, and sown in pots. Pretreatment of seeds before sowing is not necessary. Storage of seeds is difficult due to insect infestation; it is recommended to add ash or apply insecticides.

Management

In the 1950s and 1960s when intensive logging took place in forest in western Uganda, Cynometra alexandri was often considered an undesired species and treated with arboricides. The reason was that in later stages of forest succession, the slow-growing Cynometra alexandri suppressed more highly valued timber species such as Lovoa trichilioides Harms, Milicia excelsa (Welw.) C.C.Berg, Khaya anthotheca (Welw.) C.DC. and Entandrophragma spp. However, in several forests, such as the Budongo forest reserve, Cynometra alexandri is still the most dominant tree species. Trees can be managed by coppicing, pruning and pollarding.

Harvesting

Cynometra alexandri is not easy to cut because of the often large and high buttresses, the hard and heavy wood, and the often hollow boles in large trees.

Genetic resources

Cynometra alexandri is fairly widespread and locally common to even dominant in the forest. It does not appear to be liable to genetic erosion.

Prospects

The low growth rate, the hard and heavy wood, and the often poor bole shape of Cynometra alexandri are serious drawbacks for commercialization efforts. However, its fair regeneration rate in natural forest, and the high natural durability and high resistance to abrasion of the wood offer possibilities for commercial timber production for special purposes such as heavy-duty flooring, as long as long rotation cycles are acceptable. Further research is recommended on the growth rates under favourable conditions and appropriate management systems.

Major references

• ATIBT (Association Technique Internationale des Bois Tropicaux), 1986. Tropical timber atlas: Part 1 – Africa. ATIBT, Paris, France. 208 pp.

• Bolza, E. & Keating, W.G., 1972. African timbers: the properties, uses and characteristics of 700 species. Division of Building Research, CSIRO, Melbourne, Australia. 710 pp.

• Brenan, J.P.M., 1967. Leguminosae, subfamily Caesalpinioideae. In: Milne-Redhead, E. & Polhill, R.M. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 230 pp.

• Eggeling, W.J. & Dale, I.R., 1951. The indigenous trees of the Uganda Protectorate. Government Printer, Entebbe, Uganda. 491 pp.

• Fouarge, J., Quoilin, J. & Roosen, P., 1970. Essais physiques, mécaniques et de durabilité de bois de la République Democratique du Congo. Série technique No 76. Institut National pour l’Etude Agronomique du Congo (INEAC), Brussels, Belgium. 40 pp.

• Katende, A.B., Birnie, A. & Tengnäs, B., 1995. Useful trees and shrubs for Uganda: identification, propagation and management for agricultural and pastoral communities. Technical Handbook 10. Regional Soil Conservation Unit, Nairobi, Kenya. 710 pp.

• Takahashi, A., 1978. Compilation of data on the mechanical properties of foreign woods (part 3) Africa. Shimane University, Matsue, Japan. 248 pp.

Other references

• Chikamai, B.N., Githiomi, J.K., Gachathi, F.N. & Njenga, M.G., undated. Commercial timber resources of Kenya. Kenya Forestry Research Institute (KEFRI), Nairobi, Kenya. 164 pp.

• Dawe, M.T., 1910. The forests of Uganda. Journal of the Royal African Society 9(34): 120-128.

• Liben, L., 1970. Répartition géographique de trois Caesalpiniaceae forestières d’Afrique équatoriale. Bulletin du Jardin botanique national de Belgique 40: 295–298.

• Mwavu, E.N. & Witkowski, E.T.F., 2009. Population structure and regeneration of multiple-use tree species in a semi-deciduous African tropical rainforest: implications for primate conservation. Forest Ecology and Management 258: 840–849.

• Neuwinger, H.D., 2000. African traditional medicine: a dictionary of plant use and applications. Medpharm Scientific, Stuttgart, Germany. 589 pp.

• Plumptre, A.J., 1996. Changes following 60 years of selective timber harvesting in the Budongo Forest Reserve, Uganda. Forest Ecology and Management 89(1–3): 101–113.

• Sheil, D., Jennings, S. & Savill, P., 2000. Long-term permanent plot observations of vegetation dynamics in Budongo, a Ugandan rain forest. Journal of Tropical Ecology 16(6): 765–800.

• Tailfer, Y., 1989. La forêt dense d’Afrique centrale. Identification pratique des principaux arbres. Tome 2. CTA, Wageningen, Pays Bas. pp. 465–1271.

• Terashima, H. & Ichikawa, M., 2003. A comparative ethnobotany of the Mbuti and Efe hunter-gatherers in the Ituri forest, Democratic Republic of Congo. African Study Monographs 24(1–2): 1–168.

• Terashima, H., Ichikawa, M. & Sawada, M., 1988. Wild plant utilization of the Balese and the Efe of the Ituri Forest, the Republic of Zaire. African Study Monographs, Supplement 8. The Center for African Area Studies, Kyoto University, Kyoto, Japan. 78 pp.

• Wilczek, R., Léonard, J., Hauman, L., Hoyle, A.C., Steyaert, R., Gilbert, G. & Boutique, R., 1952. Caesalpiniaceae. In: Robyns, W., Staner, P., Demaret, F., Germain, R., Gilbert, G., Hauman, L., Homès, M., Jurion, F., Lebrun, J., Vanden Abeele, M. & Boutique, R. (Editors). Flore du Congo belge et du Ruanda-Urundi. Spermatophytes. Volume 3. Institut National pour l’Étude Agronomique du Congo belge, Brussels, Belgium. pp. 234–554.

Sources of illustration

• Eggeling, W.J. & Dale, I.R., 1951. The indigenous trees of the Uganda Protectorate. Government Printer, Entebbe, Uganda. 491 pp.

Author(s)

• J.R. Cobbinah, Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

• E.A. Obeng, Forestry Research Institute of Ghana (FORIG), University P.O. Box 63, KNUST, Kumasi, Ghana

Correct citation of this article

Cobbinah, J.R. & Obeng, E.A., 2011. Cynometra alexandri C.H.Wright. [Internet] Record from PROTA4U. Lemmens, R.H.M.J., Louppe, D. & Oteng-Amoako, A.A. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands.

Accessed 22 April 2026.

• See the Prota4U database.