Prota 14: Vegetable oils/Oléagineux
Journ. Bot. (Hook.) 4(30): 330 (1842).
Mimosaceae (Leguminosae - Mimosoideae)
n = 7, 2n = 26
African oil bean, Atta bean, Owala oil tree, Congo acacia, nganzi (En). Owala, mubala, arbre à semelles, acacia du Congo (Fr). Sucupira, marroné (Po).
Origin and geographic distribution
Pentaclethra macrophylla occurs in the forest zone of West and Central Africa, from Senegal to south-eastern Sudan and to Angola and on the islands of São Tomé et Príncipe.
Pentaclethra macrophylla is planted or retained along the edges of home gardens and farms mainly for its seed from which an edible oil can be extracted. Throughout the forest zone of West Africa the seeds are eaten boiled or roasted. They are also fermented to yield a snack or condiment with a meaty taste, very popular in south-western Nigeria where it is called ‘ugba’. The empty dry pods are used as fuel for cooking. Farmers protect this species on farms because its open crown does not severely affect crop growth and because some trees are leafless during the growing season. The leaves also contribute to soil fertility. Pentaclethra macrophylla wood, called ‘mubala’ or ‘ovala’, is suitable as fuel wood and for charcoal making. As few trees develop a straight trunk of harvestable size, timber of larger sizes is only occasionally available. The wood is hard and difficult to work, but suitable for poles, railway sleepers and general carpentry. Traditionally, pestles and mortars have been made from it. Ash from wood or pods is used as a mordant in the dyeing industry. In DR Congo the edible caterpillars of the giant silkworm moths Nudaurelia oyemensis (called ‘minsangula’) and Imbrasia obscura (called ‘minsendi’) feed on the leaves. Bees forage the flowers for honey. Pentaclethra macrophylla is used in Africa in traditional human and veterinary medicine. The ripe fruits are applied externally to heal wounds. Extracts of the leaf, stembark, seed and fruit pulp have anti-inflammatory and anthelmintic activity, and are used to treat gonorrhoea and convulsions, and also used as analgesic. The root bark is used as a laxative, as an enema against dysentery and as a liniment against itch. In Cameroon an infusion of the bark is used as an abortifacient. Pentaclethra macrophylla is occasionally planted along roads. It plays a role in various traditional ceremonies.
Production and international trade
Most production is for home or local consumption and no information on production and trade of oil, ‘ugba’ or timber is available.
Unfermented seed contains per 100 g: water 3–10 g, energy 2330–2540 kJ (557–607 kcal), protein 17–22 g, fat 35–52 g, carbohydrate 12–43 g, crude fibre 2.5 g. The fatty acid composition of the oil is: palmitic acid 3–4%, stearic acid 0–2%, arachidic acid 4%, behenic acid 5–6%, lignoceric acid 11–12%, oleic acid 19–29%, linoleic acid 42–54%, linolenic acid 0–3%; in addition 2 unusual long-chain fatty acids are present: hexacosanoic acid 5% and octacosanoic acid 1%. The seed contains the growth-retardant alkaloid paucine (caffeoyl-putrescine). When the seed is fermented to ‘ugba’ it is detoxified. The fermentation causes a marked reduction in protein content, and a slight increase in carbohydrate, oil and ash contents.
The heartwood is reddish brown and not always distinctly demarcated from the whitish or grey sapwood. The grain is interlocked and texture coarse. At 12% moisture content the density is 910 kg/m3. The rates of shrinkage are high, 11–16.5% volumetric. Logs should be quarter sawn before drying. At 12% moisture content, the modulus of rupture is 130–226 N/mm2, modulus of elasticity 16,000–21,150 N/mm2, compression parallel to grain 75.2–83.6 N/mm2, Janka side hardness 11,020 N, Chalais-Meudon side hardness 8.5–14.1. The wood is hard and strong, but difficult to work. It is susceptible to marine borers and occasionally attacked by termites. The silica content is less than 2%.
Medium-sized to fairly large tree up to 35 m tall; bole up to 100 cm in diameter, often crooked and low branching, with irregular, thick buttresses up to 3 m high, or without buttresses; outer bark greyish to reddish brown, thin, flaking irregularly, inner bark fibrous, yellow to orange; twigs brown stellate-hairy. Leaves alternate, bipinnately compound, 20–45 cm long; stipules needle-shaped, 3–5 mm long, caducous, with basal gland; petiole 3–6(–8) cm long, swollen and jointed at base, channeled; pinnae opposite, in 9–13 pairs, (8–)10–14 cm long, at base markedly jointed, with (6–)8–14(–20) pairs of leaflets; leaflets opposite, sessile, obliquely oblong to elliptical, 12–25 mm × 5–10 mm, apex rounded, glabrous except for scattered hairs on margins and midrib below. Inflorescence a terminal or axillary panicle up to 30 cm long, consisting of spikes, many-flowered, densely covered with brownish stellate hairs. Flowers bisexual, regular, 5-merous, small, fragrant, sessile; calyx campanulate, with broadly elliptical lobes, c. 0.5 mm long; petals oblong-lanceolate, c. 3 mm long, basally swollen and fused for c. 1 mm, yellow; stamens 5, c. 5 mm long, yellow, anthers with large gland between the thecae, staminodes 10–15, filiform; ovary superior, sessile, 1-celled, glabrous at first, upper part hairy, style extending during flowering, stigma indistinct. Fruit an obliquely linear-oblong pod up to 50 cm × 10 cm × 2 cm, woody, dark brown, tapering to the base, apex rounded, sides longitudinally ribbed, long-persistent and opening explosively on the tree and then recurving strongly, 5– 8-seeded. Seeds elliptical in outline, flattened, 3.5–7 cm × 2.5–3.5 cm × c. 1 cm, smooth, purplish brown. Seedling with hypogeal germination; cotyledons remaining in the testa; hypocotyl not developing, epicotyl 8–10 cm long, with several scales; leaves alternate, first leaf bipinnate.
Other botanical information
Pentaclethra comprises 3 species, 2 in Africa and 1 in South America. The other African species, Pentaclethra eetveldeana De Wild. & T.Durand, can be distinguished by its smaller leaflets and simple hairs. The American Pentaclethra macroloba (Willd.) O.Kuntze yields timber traded as ‘gavilán’ and is an important medicinal plant.
Growth and development
The bole is often gnarled and twisted and forked at a low level and the base is often damaged by elephants, but trees with a longer straight trunk are occasionally found. Watershoots around the base are common and the tree coppices well. The crown has been described as heavily branched and dense, but also as open and allowing crops to grow well below the tree. Some specimens are leafless during the rainy season, though the species is mostly evergreen. Pentaclethra macrophylla nodulates and fixes atmospheric nitrogen. The main flowering season in West Africa is March–April, with smaller flushes in June and November; in Liberia trees flower in February–April and fruit in September–December. The flowers are strongly fragrant, very rich in nectar and much visited by honeybees.
Pentaclethra macrophylla is common in primary forest and secondary forest and coastal savanna, often in the vicinity of creeks and rivers. It is most common at altitudes up to 500 m, although growth can be good at higher elevations where rainfall is adequate and temperatures are never cooler than 18°C. It requires a mean annual rainfall of (1000–) 1500–2000(–2700) mm and a mean annual temperature of about 25°C. It prefers medium loamy, well-drained soil. The natural distribution suggests that it is adapted to relatively acid soils. It tolerates waterlogging.
Propagation and planting
The seed is recalcitrant and should be planted immediately. Storage at 15°C can extend longevity to about 3 months. There are 50–80 seeds per kg. Mechanical scarification and soaking in water for 24 hours enhances germination. Pentaclethra macrophylla can also be propagated by cuttings, air-layering or budding. Only juvenile stem cuttings will root and are best treated with a growth hormone. Cuttings may produce seed after 4 years, budded trees after 3 years. Although direct sowing is common, better planting material is obtained from seedlings produced in nurseries and hardened off before planting.
Trees of Pentaclethra macrophylla are commonly protected and often tended in farm land, e.g. in DR Congo where it is grown on farms and on abandoned farm land to improve bush fallow. An area around the stem may be clean-weeded to facilitate collection of the seeds.
Diseases and pests
No serious diseases or pests of Pentaclethra macrophylla are known, but many insect species and pathogens attack the pods and seeds. The major insect pests are Cossus cadambae, Sitophilus spp., Spodoptera exempta and several giant silkworms. Some of the insect pests skeletonize the green pods, some bore into the pods and seeds; others lacerate the pods, causing lesions that allow fungal and bacterial pathogens to invade the seeds.
Fruits are available at most periods of the year because the large woody pods are persistent. Harvesting pods is an arduous and dangerous task and collectors may charge as much as half of the yield as their fee.
Handling after harvest
The seeds of Pentaclethra macrophylla are roasted or boiled, or fermented to produce ‘ugba’. The seeds are boiled for 3–12 hours; then the seedcoat is removed. When the cotyledons are cooled to room temperature they are sliced into small pieces of 4–5 cm × 1–2 mm and washed with water. The slices are boiled for 1–2 hours, cooled and soaked in water for 10 hours. Then the slices are drained in a basket lined with banana leaves. The drained slices are wrapped in blanched leaves of banana or Mallotus oppositifolius (Geiseler) Müll.Arg. and incubated at ambient temperature for 4–6 days when prepared for use as a snack or sidedish, or for 7–10 days when prepared as a condiment for soups. The fermentation is proteolytic and proceeds under alkaline conditions. It is caused mainly by Bacillus subtilis, but other Bacillus spp. are also involved, while other bacteria may be present as contaminants.
Although not immediately endangered by genetic erosion, numbers of Pentaclethra macrophylla have declined strongly in some areas. In Nigeria stands are now largely confined to the south-eastern region and even there regeneration rates seem inadequate. No collections of genetic resources exist. However, the National Centre for Genetic Resources and Biotechnology and the Forestry Research Institute of Nigeria have initiated the study, collection and conservation of edible plant resources, including Pentaclethra macrophylla.
The domestication of Pentaclethra macrophylla as a tree crop in agroforestry has been recommended. Selection of trees with non-shattering pods or with pods that shatter simultaneously and the development of pruning methods that make harvesting easier are desirable.
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Sources of illustration
• Villiers, J.-F., 1989. Leguminosae - Mimosoideae. Flore du Gabon. Volume 31. Muséum National d’Histoire Naturelle, Paris, France. 185 pp.
• Wilks, C. & Issembé, Y., 2000. Les arbres de la Guinée Equatoriale: Guide pratique d’identification: région continentale. Projet CUREF, Bata, Guinée Equatoriale. 546 pp.
Correct citation of this article:
Oboh, G., 2007. Pentaclethra macrophylla Benth. In: van der Vossen, H.A.M. & Mkamilo, G.S. (Editors). PROTA 14: Vegetable oils/Oléagineux. [CD-Rom]. PROTA, Wageningen, Netherlands.
1, base of bole; 2, leaf; 3, inflorescence; 4, fruit; 5, seed.
Redrawn and adapted by Achmad Satiri Nurhaman
fruit and inflorescence
open fruit with seeds