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(Afrikaans) : haak-en-steek
(Arabic) : samar, sammar, samor, samra, sayyal, seyal, seyyal
(English) : karamoja, umbrella thorn
(Hindi) : Israeli babool
(Ndebele) : isanqawe, umsasane, umshishene, umtshatshatsha
(Nyanja) : mzunga, nsangu, nsangunsangu, nyoswa
(Somali) : abak, kura
(Swahili) : mgunga, mugumba, munga
(Tigrigna) : akba, akiba, alla, aqba
(Tongan) : mukoka, muzungu, ngoka
(Tswana) : mosu, mosunyana
(Zulu) : umSasane
Acacia tortilis is a small to medium-sized evergreen tree or shrub that grows up to 21 m tall; well-developed multiple boles support a flat-topped or rounded, spreading crown; bark grey to black or dark brown, rough, fissured or smooth; young branchlets densely pubescent or glabrous to subglabrous and red to brown; spines paired, 2 types-long, straight and white, or short, brownish and hooked; they range from 1.2 to 8 cm in length. Leaves glabrous to densely pubescent, glandular, short at 1.25-3.75 cm long; petiole 0.2-0.9 cm long, with a gland; rachis 0.3-2 cm long, glabrous to densely pubescent, with a small gland at the junction of the apical pair of pinnae; pinnae 2-10 pairs; leaflets 4-22 pairs per pinnae, 0.5-4 (6 max.) x 0.2-1 mm, glabrous to densely pubescent on the underside; margins with or without cilia, linear to linear oblong. Inflorescence globose heads; peduncle white, pubescent, 0.4-2.5 cm long, with involucel on the lower half; flowers white or pale yellowish-white, sessile or shortly pedicellate, scented, 0.5-1.1 cm in diameter, on axillary peduncles; calyx 1-2 mm long; corolla 1.5-2.5 mm long. Pods variable, indehiscent, spirally twisted or rarely almost straight, 7-10 cm long, 6-10 (max. 13) mm broad, longitudinally veined, leathery, glabrous to tomentellous or villous, somewhat constricted between the seeds; seeds oblique or parallel to long axis of pod, 4-7 x 3-6 mm, compressed; areole 3-6 x 2-4 mm. The generic name ‘acacia’ comes from the Greek word ‘akis’, meaning a point or a barb. The name ‘tortilis’ means twisted and refers to the pod structure.
Ecology and distributionHistory of cultivation
The species is widespread in the Sahel, in woodlands and in the savannah. It is indigenous to southern Israel, Somalia, Sudan, Yemen, parts of Kenya, Tanzania and Saudi Arabia. Distinct subspecies have been recorded in different ecological regions: A. tortilis ssp. spirocarpa in the Sahel, the Middle East, East Africa and Sudan, and A. tortilis ssp. heterantha in South Africa; A. tortilis ssp. raddiana is a comparatively new introduction to India, through the Central Arid Zone Research Institute in Jodhpur. At present it is planted extensively in northern tropical thorn forest zone in the arid areas of Andhra Pradesh, Gujarat, Haryana, Rajasthan and Tamil Nadu, and southern arid districts of Punjab.
A. tortilis is drought resistant, can tolerate strong salinity and seasonal waterlogging and generally forms open, dry forests in pure stands or mixed with other species. The long taproot and numerous lateral roots enable it to utilize the limited soil moisture available in the arid areas. It tolerates a maximum temperature of 50 deg. C and a minimum temperature close to 0 deg. C.
Native : Angola, Botswana, Egypt, Eritrea, Ethiopia, Iran, Israel, Kenya, Mozambique, Namibia, Qatar, Saudi Arabia, Somalia, South Africa, Sudan, Swaziland, Tanzania, Uganda, United Arab Emirates, Zambia, Zimbabwe
Exotic : Benin, Burkina Faso, Cameroon, Chad, Cote d'Ivoire, Gambia, Ghana, Guinea, India, Liberia, Mali, Mauritania, Niger, Nigeria, Pakistan, Senegal, Sierra Leone, Togo
Biophysical limitsAltitude: 0-1 000 m, Mean annual temperature: 23.4-31.3 deg. C, Mean annual rainfall: 100-1 000 mm. Soil type: The tree favours alkaline soils and grows in sand dunes, sandy loam, rocky soils and other soils that drain well. It also does well on light brown, sandy soil with little or no calcium carbonate, and pH ranges of between 7.95-8.30.
A. tortilis is a hermaphrodite. Gravity or propulsion from drying dehiscent pods initiates seed dispersal. In India, trees flower between May and June and fruit by mid July, and in Nigeria flowers appear in May-June and fruits in July.
Propagation and managementPropagation methodsA. tortilis can be grown from potted seedlings or by direct seeding. The seeds have a hard testa and require pretreatment before sowing. Boiling water is poured over the seeds before they are soaked in water for 24 hours. Scarification with 50% concentrated sulphuric acid for 40-50 minutes followed by washing in cold running water and then drying in the shade overnight is an alternative method. Seeds of various dimensions have varying scarification requirements. This method gives the maximum germination rate, about 95%. It is further reported that older seeds give healthier seedlings compared with fresh seeds. The pretreated seeds are sown in cylindrical metallic containers 10.2 cm in diameter and 30.5 cm long, filled with equal proportions of finely powdered farmyard manure, tank silt and soil that is sieved through a fine wire mesh. Two seeds are sowed in each container. The sowing depth should not be more than to 4 cm; otherwise, seedling emergence will be adversely affected. Germination starts on the 4th day and is mostly completed over 10 days, although it may continue for 60-70 days. Seedlings should be watered twice a day. Shade, when provided during the summer months, reduces the water requirement of the plants by 9.6% as compared with those grown in the open. Seedlings raised in metallic containers and planted in cemented beds, which are immersed in water, require 29% less water than those kept in earthen beds. In the long run, metallic containers are cheaper than the other types of containers and last longer (about 12 years). Seedlings are planted out when 0.5-1 m high and require initial weeding to facilitate growth. Plants less than 2 years old are damaged by frost and are tender to hot, desiccating winds.
Initial integrated soil and water conservation measures help check mortality and boost early growth and establishment of trees in very unfavourable conditions. The fast-growing tree develops a long lateral root system and creates problems in marshy fields, paths and roadways. It grows fairly well even on shallow soils less than 25 cm deep. However, the plant assumes shrubby growth and must be widely spaced for the lateral root growth. It responds vigorously to felling by producing numerous coppice shoots, provided there is no interference from browsing animals. Lopping of entire branches does not seem to affect the vitality of the tree. Studies conducted on its nitrogen-fixing ability, photosynthetic efficiency, seedling morphology and drought resistance have shown that it is relatively a better species than Prosopsis juliflora. A tree 6-7 years old on average yields about 5-6 kg of clean seeds. Planting is done in pits 60 cm deep dug at a spacing of 5 x 5 m and filled with weathered soil. If raised as a windbreak, 3 rows are planted spaced at 9 x 10 m, and 50 gm/plant of ammonium sulphate is applied at watering time. Plants grow to about 1.5 m in 2 years, should be protected from grazing and mulching should be practised. 2 weedings in the 1st year and 1 in the 2nd year are considered sufficient.
Seed storage behaviour is orthodox; viability can be maintained for several years in hermetic storage at 10 deg. C with 4.5-9% mc. There are about 12 000-25 000 seeds/kg.
Functional usesProductsFood: In Kenya, the Turkana make porridge from the pods after extracting the seed; the Maasai eat the immature seeds. Fodder: It is an important source of fodder for cattle in India, West Africa, Somalia and Ethiopia. Foliage and fruits form important browse. The leaves are fed green as well as dry. A 10-year-old A. tortilis yields about 4-6 kg dry leaf and 10-12 kg pods per year. Fruits are preferred for stall-fed animals and should be ground to make them more nutritious. Crude protein and digestibility coefficients of A. tortilis are about 18% and 46.2%, respectively. Over 90% of the flowers abort and drop to the ground, providing additional important forage. Fuel: A. tortilis starts producing fuelwood at the age of 8-18 years, at the rate of 50 kg/tree. Its fast growth and good coppicing behaviour, coupled with the high calorific value for its wood (4400 kcal/kg), make it suitable for firewood and charcoal. Timber: The sapwood and heartwood are white and lustrous, with the heartwood aging to reddish-brown. Growth rings are distinct and separated by brown lines. The wood is moderately soft, not very strong, and is readily attacked by decay-causing fungi and insects. It should be promptly converted after felling and subjected to rapid drying conditions. The timber is not durable in the open but moderately so under cover. It is used for planking, boxes, poles, moisture-proof plywood, gun and rifle parts, furniture, house construction and farm implements. It is believed that Noah of the Old Testament made his ark from the wood of A. tortilis. Tannin or dyestuff: The bark is reported to be a rich source of tannin. Poison: A. tortilis is a powerful molluscicide and algicide; in Sudan, fruits are placed in fish ponds to kill the snail species that carry schistosomiasis, without affecting the fish. Medicine: The dried, powdered bark is used as a disinfectant in healing wounds; in Senegal it serves as an anthelmintic. In Somalia the stem is used to treat asthma. Seeds are taken to treat diarrhoea.
Erosion control: Due to its drought hardiness and fast growth, the species is considered more useful than many indigenous species growing in the arid zone of India. It is a promising species for afforesting shifting sand dunes, refractory sites, hill slopes, ravines and lateritic soils. Shelter or shade: In India, it has been grown successfully with Azadirachta indica in shelterbelts. Nitrogen fixing: A. tortilis nodulates and hence is nitrogen fixing. Boundary, barrier or support: The thorny branches are suitable material for erecting barriers. Intercropping: Poor herbaceous growth under A. tortilis has been reported. In India clusterbean, cowpea and mothbean are said to have failed when planted in association with A. tortilis. However, yields of mungbean, and sorghum have been shown to increase when lateral roots of A. tortilis are trenched.
Pests and diseasesPowder pest beetles (Sinoxylon anale and S. crassum) are serious pests of A. tortilis timber in India. They can reduce felled timber to dust in weeks. Prophylactic treatment is recommended to protect the timber, with 1.5% lindane 20 EC water emulsion or 1.5% endosulfan 35 EC water emulsion. Other recorded pests are Callosobruchus chinensis and Caryedon gonogara (bruchid). In plantations and seed production areas, pod and seed insects can be controlled by treating individual branches with 0.25% endosulfan or fenitrothion water emulsions. Seed stored in gunny bags can be dusted with 5% folithion for short-period treatment. If the seeds are to be stored for longer periods, 10% BHC should be applied with a duster. Fumigation with carbon disulphide, aluminium phosphide or chlorosal will kill seed- and pod-boring bruchids. Pyrethrum mixed with seed in a seed-dressing drum also acts as an insect repellent. A. tortilis is also susceptible to attack by other beetles, caterpillars and blight.
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