Loudon, Hort. brit.: 277 (1830).
Mimosaceae (Leguminosae - Mimosoideae)
2n = 24, 26
Mimosa biglobosa Jacq. (1763), Parkia africana R.Br. (1826), Parkia clappertoniana Keay (1955), Parkia filicoidea auct. non Welw. ex Oliv.
African locust bean (En). Néré, arbre à farine, caroubier africain (Fr). Farroba (Po).
Origin and geographic distribution
Parkia biglobosa occurs in a belt between 5°N and 15°N, from the Atlantic coast in Senegal to southern Sudan and northern Uganda. The belt is widest in West Africa (maximum 800 km) and narrows to the east. It was probably introduced to São Tomé and Principe. Trial plantations have been established in Tanzania, and African locust bean was introduced to the Caribbean region over 200 years ago, probably as a consequence of the slave trade, and later possibly to Guyana. The use of the fermented beans of African locust bean dates back many centuries and was already described in the 14th Century.
African locust bean is a multipurpose tree that is as highly valued as shea butter tree (Vitellaria paradoxa C.F.Gaertn.). Fermented seeds (‘soumbala’, ‘dawadawa’, ‘netetu’) serve primarily as a condiment for seasoning sauces and soups. Roasted seeds are used as a coffee substitute known as ‘Sudan coffee’ or ‘café nègre’. Ground seeds are mixed with Moringa oleifera Lam. leaves to prepare a sauce, and are also used to make doughnuts. The mealy pulp from the fruits is eaten or is mixed with water to make a sweet and refreshing drink rich in carbohydrates. Boiled pods are used to dye pottery black; the ash is applied as a mordant. The bark is rich in tannins and may be used for tanning hides, but the resulting leather is often of moderate quality especially with regard to colour, which is often reddish, uneven, and darkens when exposed to light.
The leaves are sometimes eaten as a vegetable, usually after boiling and then mixed with other foods such as cereal flour. Young flower buds are added to mixed salads.
In West Africa the bark, roots, leaves, flowers, fruits and seeds are commonly used in traditional medicine to treat a wide diversity of complaints, both internally and externally, sometimes in combination with other medicinal plants. The bark is most important for medicinal uses, followed by the leaves. Medicinal applications include the treatment of parasitic infections, circulatory system disorders, such as arterial hypertension, and disorders of the respiratory system, digestive system and skin. In veterinary medicine, a root decoction is used to treat coccidiosis in poultry. Green pods are crushed and added to rivers to kill fish. The nutritional value of the fish is not adversely affected so long as they are cooked or dried.
The fruit pulp is used as an ingredient of feed for pigs and dogs. The seeds are added to poultry feed after treatment to remove their antinutritional properties. The leaves are a useful, but not very palatable fodder. They should be mixed with other feed because the concentrations of phosphorus, magnesium and sodium are too low. The wood is suitable for making kitchen implements, such as mortars, pestles and bowls, and handles of hoes and hacks, and it is occasionally also used for house building, mainly for indoor construction. It is also used as firewood, and may be suitable for paper production. The fibres of pods (husks) and roots are used as sponges, strings of musical instruments and for the production of small baskets. Burnt pod husks are used in Senegal as an adulterant of, or additive to, tobacco (adding pungency).
African locust bean has a reputation for soil improvement; its leaves are applied as green manure. It is also important in apiculture, being a good source of nectar and suitable for the placement of hives. It may serve as a decorative avenue tree.
African locust bean is very important in West African culture. It plays a role in all major rituals, including those associated with birth, baptism, circumcision, marriage and death.
Production and international trade
In northern Nigeria the annual production of seeds is estimated at 200,000 t. The products of African locust bean are not important in international commercial trade. However, local trade is important in West Africa, especially in the Sahel region, where the dried or fermented seeds are often transported far from the sites of production, often across country borders.
The yellowish fruit pulp is very rich in carbohydrates (ca. 80%), which makes it an excellent energy source. The seeds of African locust bean contain antinutritional factors and have to be processed before use as food or livestock feed. Boiled and fermented seeds contain 35% proteins, 29% lipids, 16% carbohydrates and have good organoleptic properties and a positive effect on intestinal flora. The seeds are good sources of protein, fat and calcium, but contain a non-toxic oil of variable composition. Some sources indicate arachidic acid as the most abundant fatty acid, accompanied by behenic, stearic, palmitic and linoleic acids; other sources mention oleic acid as the most important component (35–50%) with, in addition, equal amounts of behenic, oleic, palmitic and stearic acids.
An alcoholic extract of crude seeds showed anti-hypertensive activity and contractile effect on smooth muscles of the intestine, and increased the tonus and mobility of the uterus. Ichthyotoxic and molluscicidal activities have been recorded for the seeds due to the presence of saponins.
The bark, leaves and pod husks are rich in tannins, which in general have anti-diarrhoeal and activities. In tests with mice, analgesic and anti-inflammatory activities have been demonstrated for bark extracts. The aglycone flavonoids in the leaves have spasmolytic activity on smooth muscles, and also vasodilatory and antiseptic effects. Coumarin derivatives in leaf extracts have anticoagulant activity.
The wood is relatively hard and solid, but not very durable, whitish to yellowish or dull brown. The sapwood is often indistinctly demarcated from the slightly darker heartwood. The density is 550–650 kg/m³ at 15% moisture content.
Adulterations and substitutes
Fermented seeds of pigeon pea (Cajanus cajan (L.) Millsp.), baobab (Adansonia digitata L.) and red sorrel (Hibiscus sabdariffa L.) are used as a substitute for fermented Parkia biglobosa seeds in Burkina Faso; in Benin, those of Prosopis species are used.
Medium-sized tree up to 20(–30) m tall; taproot often present, lateral roots up to 10(–20) m spreading from bole; bole usually straight and robust, cylindrical, up to 130 cm in diameter, often branching low; bark distinctly longitudinally fissured, often with more or less regular scales between the fissures, thick, ash-grey to greyish-brown, slash fibrous and reddish-brown, exuding an amber gum; crown dense, wide spreading and umbrella-shaped, consisting of heavy branches. Leaves alternate, bipinnately compound, up to 30(–40) cm long; stipules absent; petiole 4–12.5 cm long, swollen at base and there with an orbicular gland; rachis with a caducous awn at apex, bearing up to 17 pairs of pinnae, with a gland between the terminal pinnae; pinnae with 13–60 pairs of leaflets; leaflets sessile, oblong, 8–30 mm × 1.5–8(–10) mm, very unequal at base with a proximal auricle, rounded or obtuse at apex, glabrous but slightly ciliate near apex. Inflorescence a pendulous head arranged racemosely; peduncle 10–35 cm long; turning salmon-pink, many-flowered. Flowers bisexual, male or sterile, sessile but pseudopedicellate by the fusion of the bases of calyx, corolla and stamens, calyx and corolla tubular, 5-lobed; bisexual flowers in the distal portion of the capitulum, 10–17 mm long, with 10 stamens long exserted and a superior, 1-celled ovary, style filiform, stigma cup-shaped; male flowers in the basal portion of the capitulum, 6–7 mm long, with stamens not exserted, nectariferous; sterile flowers at the extreme base of the basal portion of the capitulum, 6–7 mm long, with rudimentary stamens. Fruit a linear-oblong pod 12–35 cm × 1.5–2.5 cm, slightly falcate, with stipe of 1–4 cm at base, subcylindrical, glabrous and smooth, usually brown when ripe, 5–23-seeded. Seeds embedded in yellowish endocarp, globose-ovoid, slightly compressed, 0.5–1.5 cm long, with distinct pleurogram on lateral face, testa hard, smooth, glossy dark brown.
Other botanical information
Parkia comprises about 30 species and has a pantropical distribution. Only 3 species, all belonging to the section Parkia, occur in continental Africa, and a fourth one on Madagascar. The African Parkia species seem to be closely related. Parkia biglobosa is found in savanna woodland of the Sudanian region, whereas the other 2 continental African species (Parkia bicolor A.Chev. and Parkia filicoidea Welw. ex Oliv.) are principally rain forest species.
- Macroscopic characters:
Heartwood yellowish to pale brown, usually indistinctly demarcated from the whitish to pale yellowish sapwood. Grain straight or slightly interlocked. Texture moderately coarse and uneven. Wood with unpleasant odour when fresh.
- Microscopic characters:
Vessels diffuse, often in pairs, large. Parenchyma abundant, paratracheal aliform and confluent and apotracheal in marginal bands.
Growth and development
The seedling shows semi-hypogeal germination, the testa splitting but remaining associated with the fleshy, pale green cotyledons. The first leaf is a cataphyll, and subsequent juvenile leaves are bipinnate with usually 3 pairs of pinnae. The whitish to yellowish taproot develops first during germination and gives rise to lateral roots. Growth is comparatively fast: seedlings may reach a height of 1 m in 1 year, and young trees of superior provenances can reach 7 m in 6-year-old plantations. Tree development is in accordance with Champagnat's architectural model: the trunk is formed by superposition of renewal shoots from lateral buds; the new shoot is initially orthotropic but later becomes plagiotropic; the phyllotaxy is spiral.
Trees start flowering at 5–7 years while still comparatively small. They reach their maximum height after 30–50 years, and can reach an age of 100 years. African locust bean flowers in the dry season in the Sahel region from December to April, slightly earlier in less dry regions. Flowering coincides with loss of leaves; new foliage develops after peak flowering. The flowering period lasts 3–8 weeks depending on the region. Mature fruits develop by April to May. However, 2 periods of flowering and fruiting per year may occur.
Anthesis commences during the afternoon; pollen is shed at dusk and secretion of nectar also reaches a maximum then. Flowers begin to wilt in the night. Bats are the main pollinators, but insects, such as bees and, less often flies and moths, also frequently visit the capitula and pollinate flowers. The flowers are protandrous, which facilitates cross-pollination.
Although humans are probably the main dispersers of seeds today, parrots, hornbills, monkeys, goats, antelopes, squirrels and other rodents also play an important role in seed dispersal.
African locust bean is protected and planted in agricultural fields and wasteland in savanna regions. It tolerates a wide variety of climatological conditions, the principle constant being a dry season of 5–7 months/year. It may grow in regions with an annual rainfall of 500–800 mm in the Sahel, but occurs in regions with much higher rainfall as well, e.g. 2200 mm in Guinea Bissau, and it has even been recorded in regions with over 3500 mm in Sierra Leone and 4500 mm in Guinea. It prefers regions with a mean annual temperature of 26–28°C, but tolerates lower temperatures and occurs up to 1350 m altitude. Although it prefers deep soils with good drainage and fertility, African locust bean can also be found on shallow lateritic soils, stony slopes and rocky hills.
Propagation and planting
Propagation is mainly by seeds, and these are orthodox. The seeds, with a number of 4500–5000/kg, are still viable after 8.5 years with a germination rate of 78.5% when kept at 4°C and 60% relative humidity. The seeds may be treated with concentrated (97%) sulphuric acid for 10 minutes to break dormancy, and subsequently immersed in water for 24 hours. Germination at an average rate of 95% for freshly collected seeds starts 48 hours after sowing, usually in pots. Small farmers usually soak seeds in water overnight. Seedlings need watering twice a day, and weeding once every 2 weeks. After sowing in seed-beds, young seedlings of 3 days old can be transplanted into pots. Seedlings reach 20–25 cm tall after 20 weeks in the nursery, and are then planted out into the field. Direct sowing is possible, but the success rate depends on soil moisture and the degree of insect and rodent damage, these pests being attracted by the strong smell of germinating seeds.
Preliminary ploughing of the soil contributes to proper establishment of seedlings in the field, with a success rate up to 82% four years after planting. Spacing is usually 10 m × 10 m.
Vegetative propagation of African locust bean is also possible. Grafting, cuttings taken from seedlings, and marcotting of 11–25 years old trees showed good results in Burkina Faso and Nigeria. Experimental in-vitro propagation by meristems of young seedlings has given a success rate of 72% in the United Kingdom.
Thinning of older trees is practised in Burkina Faso, Benin, Mali and Nigeria to promote fruit production and reduce the effect of shade on associated agricultural crops. In Burkina Faso, a decline in millet and sorghum yields occurred when cultivated under African locust bean trees. In some regions of Burkina Faso, regular weeding, and establishment of fire breaks, are customary in plantations of African locust bean.
Diseases and pests
Fungal infections of leaves by Cercospora sp. have been recorded in Guinea, and by Hypoxylon rubiginosum and Phyllachora leonensis in Sierra Leone. Attacks by a basidiomycete of the genus Phellinus may cause desiccation of trees. Infection by loranthaceous hemiparasites of the genera Tapinanthus and Agelanthus is widespread and may eventually result in the death of heavily infected trees.
Fruits are normally collected in April and May. Harvesting is either done from the ground using long-staked cutters, or by climbing the trees. When seeds are collected for the production of young plants, 25–30 individual trees of superior stature, good health and at least 100 m apart are selected.
The annual production of fruits varies between 25–130 kg/tree, depending on year and site. Average annual production of seeds is 900 kg/ha, of pulp 2.2 t/ha and of husks 1.9 t/ha. The production of trees planted in agricultural fields is on average higher than that of trees growing in wasteland.
Handling after harvest
The fruits collected for plant production are transported in jute sacks. The fruit valves are opened by removing the fibrous strand extending from the base to the apex, and the seeds with adherent pulp are removed. These are pounded and sieved through a coarse mesh, and subsequently washed to remove the pulp completely. Floating elements are eliminated. The seeds are then dried and impurities removed. The methods for seeds without pulp are boiled for 24 hours, subsequently cleaned, and boiled a second time for 0.5–2 hours. The seeds are then fermented for 2–4 days in a container covered by leaves or plastic. Fermentation is usually a spontaneous bacterial fermentation under alkaline conditions. main bacteria involved are species of Bacillus, but others include species of Lactobacillus, Micrococcus and Staphylococcus. The final product is obtained after sun drying for one day. During drying, salt or ash can be added to improve the flavour.
Seed collecting missions were organized by the Centre National de Semences Forestières (CNSF), Burkina Faso, in 1990 and 1995 in 12 countries (Senegal, Guinea, Côte d'Ivoire, Mali, Burkina Faso, Ghana, Togo, Benin, Niger, Nigeria, Cameroon and Chad). This resulted in the establishment of a seedbank in Burkina Faso, and in a study of the morphological and genetic variability of Parkia biglobosa, which showed that the species has a comparatively high genetic diversity and an important intraspecific morphological variability, mainly present within populations. This enables the conservation of maximum phenotypic diversity by sampling a large number of specimens in a few populations of different parts of the area of distribution.
African locust bean is one of the comparatively few tropical plant species which has been subject to thorough studies concerning its biology and utilization. It has considerable socio-economic importance, and therefore its weakly organized local management deserves more attention, as well as initiatives to improve its products. It is, for example, desirable that appropriate technology be developed for industrial processing of the seeds and pulp. An evaluation of the genetic constitution and production capacity of Parkia biglobosa populations within the entire area of distribution is needed as a basis for developing sustainable management systems while meeting the demand for the products.
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Sources of illustration
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Correct citation of this article:
Sina, S. & Traoré, S.A., 2002. Parkia biglobosa (Jacq.) R.Br. ex G.Don. Record from Protabase. Oyen, L.P.A. & Lemmens, R.H.M.J. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, the Netherlands.
Parkia biglobosa – wild and planted
1, leaf; 2, branchlet with inflorescences; 3, bisexual flower; 4, male flower; 5, branchlet with fruit; 6, seed
Redrawn and adapted by M.M. Spitteler
sectioned inflorescence, red anthers protruding at onset anthesis at 17.00 hours
‘soumbala’, fermented seeds sold for cooking