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Acacia seyal Del. |
 
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Leguminosae
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Author: Le Houérou
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Small, slender tree, reaching 6-15 m in height, with a stem diameter up to 60 cm, develops a characteristic umbrella-shaped canopy in adult individuals, usually thin and rather scarce foliage. Bark is usually smooth, pale green to greenish yellow when young or orange on exposure after the old bark has sloughed off. Bark smooth, peeling, rust-red or pale-green (both types may coexist in any population), covered with a pruinous, rusty, powdery coating. Bright red mottled slash, exuding a yellowish gum. Twigs with many small reddish glands and paired axillary thorns, up to 7 cm long, narrow and straight, vulnerant-sharp-ended and grey in color. Leaves dark green, with 4-12 pairs of pinnae having each 10-22 pairs of leaflets. Rachis up to 8 cm long clustered by 2 or 3. Flowers clustered by 2-3 with bright yellow globose heads ca 1.5 cm in diameter on peduncles about 3 cm long starting from the leaves axils. Pods hanging, slightly curved, dehiscent, light brown when mature, 10-15 cm long by 1 cm wide at the bottom, containing 6-10 seeds each. It is a gregarious species, occasionally forming impenetrable thickets of almost pure stands. Usually found in the 400 to 800 mm MAR belts. A. seyal grows on fine-textured soils, it may tolerate periodical floodings. Widespread in northern tropical Africa, extending to Egypt. A. seyal is a typical tree of the South Sahelian and North Sudanian ecozones, across the whole Sahel from the Atlantic Ocean to the Red Sea and beyond to the South Arabian Peninsula and East and South Africa. In East Africa, however, there is a particular variety, var. fistula (Schweinf.) Oliver, with myrmecophilous, perforated, hollow, swollen-based thorns, or "ant-galls" reminding those of A. drepanolobium, (the whistling thorn), but with elongated bilobate whitish fistulae in A. seyal, whilst those of A. drepanolobium are spherical and blackish ; both, however, are characteristic of clay soils. var fistula, is not unknown to the Rep.of Sudan (Rashad, Umm Ruwaba, Sennar, Gedaref and to the South of El Obeid). Var. fistula is particularly tolerant to flooding (Wickens, in Litt., 2000). In the Sahara and North Sahel A. seyal has been confused for decades with A. ehrenbergiana which looks quite similar. Planting has been little developed as native stands are still common place. If some control is necessary, repeated burning or a basal bark spray with 2,4,5-T will help but will not give full control (Ivens, 1970). The bark is the most valuable part of Acacia seyal. It is extensively used for feeding cattle, goats and sheep during the dry season. The bark is thick, smooth and relatively soft when fresh. In the dry months of February and March in Kenya, thick branches are thrown to the ground and animals browse the bark and eat the leaves, which, however, are relatively few at that time. Often the whole tree is cut to a height of 1.5 to 2 m and new growth arises from the previous cut. As animals often browse the bark of standing trees, deformation is common. Round service-wood, poles, posts, building material, fuel wood, fuel is subject to wood borers and readily reduced to dust when stored, "Zeribas" (= "Bomas") building, fencing, dead and live fencing, browsing of leaves, twigs and pods, branches are often pollarded by shepherds. A. seyal, also produces a gum which, in spite of being of an inferior quality than that of A. senegal, is still marketed in the Rep. of Sudan (3,000-6,000 t/a). The smoke of A. seyal's wood is said to be insect-repellent. In human medicine, A. seyal leaves, gum and bark are used in phytotherapy for haemorrhage,, colds, diarrhoea, gastro-intestinal disorders, jaundice, biliary diseases, syphilis, headaches and as emollient, astringent, for burns and ophtalmia. Nutritional Quality and Animal Production Animals will eat up to 5.5 kg. of bark a day, sufficient for maintenance and the production of 4.5 litres of milk. The crude protein content of the bark is 10.6 percent in February and 4.1 percent in August. The calcium values are very high, with over 4 percent in February, but the phosphorus content of under 0.1 percent was low (Dougall and Bogdan, 1958). CP in pods and leaves is ca 18 % on the DM, net energy is around 6.5 MJ / kg DM, P content is ca. 0.14 % in leaves and 0.34 % in pods.
Berhaut 1975 ; El Amin 1973 ; El Amin 1990 ; Giffard 1974b ; Geerling 1982/88 ; Kerharo & Adam, 1974 ; Cissé 1980a, Cissé 1980b ; Baumer 1983 ; Von Maydell 1983/86 ; Dommergues et al. 1999. |