1. Family: Fabaceae Lindl.
    1. Genus: Senegalia Raf.
      1. Senegalia senegal (L.) Britton

        Gum arabic is harvested from Senegalia senegal because it has superior properties over other 'acacias', and hence it is this gum that has dominated international trade. Currently the biggest markets for Senegalia senegal gum are the European Union, North America (mainly the USA) and the Indian Subcontinent (mainly India). The UK imported 1,253 tonnes in 1998. Sudan, Nigeria and Chad are the three biggest sources of this gum.

    [KSP]

    Kew Species Profiles

    General Description
    Gum arabic has been used for at least 4,000 years in the preparation of food, in human and veterinary medicine, in crafts and as a cosmetic.

    Harvested from Senegalia senegal, gum arabic has superior properties over other 'acacias', and hence it is this gum that has dominated international trade. Currently the biggest markets for Senegalia senegal gum are the European Union, North America (mainly the USA) and the Indian Subcontinent (mainly India). The UK imported 1,253 tonnes in 1998. Sudan, Nigeria and Chad are the three biggest sources of this gum.

    Gum arabic is traded in large quantities, and is grouped into three grades. Grade 1 (the best) is in large, round or worm-shaped pieces and is white/pale or brownish yellow. Grade 2 gum is in rounded, worm-shaped or branched pieces, and is smaller in size and generally darker in colour than the top quality. The poorest grade gum (Grade 3) is in the form of small brown grains.

    Species Profile
    Geography and distribution

    Acacia senegal is found growing in Mauritania, Senegal, The Gambia, Ghana, Burkina Faso, Côte d'lvoire, Mali, Niger, Nigeria, Cameroon, Democratic Republic of the Congo, Central African Republic, Rwanda, Chad, Sudan, Ethiopia, Somalia, Uganda, Kenya, Tanzania, Mozambique, Angola, South Africa, Namibia, Oman, Pakistan, and India. It has been introduced to Egypt, Australia, Puerto Rico, the Virgin Islands and elsewhere.

    This species can grow on light sandy soil, slightly loamy sand and skeletal soils (lithosols) but it prefers coarse-texture soils such as fossil dunes, with a 300 to 400 (maximum 700) mm annual rainfall. It can also grow in areas that receive 100 to 950 mm annual rainfall, but these extremes reduce the production of gum. It can tolerate five to eleven months of drought. It can survive temperatures of 45˚C, dry wind and sandstorms, but cannot withstand frost. The best sites for the species have a pH of 5 to 8. The altitude ranges from 100 to 1,700 m above sea level in the Sudan to 1,950 m around Nakuru in Kenya.

    Description

    Overview: A low branching shrub or small tree to 7 m high (maximum 15 m). The tree flowers during the rainy season and loses its leaves during the dry season. When water is only available at great depth, deeply penetrating tap roots can develop, and the tree will grow considerably larger than normal.

    The bark of Acacia senegal is yellow to brown and smooth in young trees, becoming dark grey, gnarled and cracked on older trees. It is armed with recurved prickles just below the nodes, in pairs or in groups of three.

    Leaves: The leaves are 3.5 to 8 cm long, with 3 to 8 pairs of pinnae. The rachis (main stem of the compound leaf) sometimes bears prickles. The pinnae are 1.5 to 2.5 cm long with 5 to 25 pairs of leaflets per pinna. The leaflets are 1 to 9 mm long, 0.5 to 3 mm wide, elongated-oval shape, sparsely hairy or smooth on both surfaces.

    Flowers: The flowers are borne on spikes 3 to 8.5 cm long.

    Fruits: The hairy fruits are yellow-brown, flat and papery, 1.8 to 9 cm long, 1.2 to 3.4 cm wide, 2 mm thick and open on maturity to discharge the seeds.

    There are four varieties of A. senegal . These differ in the presence or absence of hair on the axis of the flower spike, colour of the axis, shape of pod tips, number of pinnae pairs, trunk branched or not branched from the base and shape of the crown, as well as their geographical distribution.

    The germination of seed is slow and young plants usually have to contend with competition from grass and browsing stock. Those which survive will begin to yield gum at three to four years of age. The best yields in West Africa come from trees 12 to 15 years old and up to 20 cm diameter. In Kordofan trees aged four years are opened for tapping, which continues to the age of 20 or older, but elsewhere in Sudan six to 18 years is usual. The best yields come from trees in areas with an annual rainfall of only 250 to 300 mm. Trees die at an age of 25 to 30 years, by which time they will have succumbed to borers and termites.

    Many common names

    SEPASAL records 196 local names for this plant. Common names include: tur, tulh, harheyr (Jibbali); temmar (Dhofari arabic); Sudan gum, Kordofan gum (English); gommier, gommier vrai, gomme blonde, gomme blanche (French); khor (Punjab); kumta (Rajputana); Senegal gum, Somali gum (in the trade industry).

    Threats and conservation

    Other than in the case of Sudan, where pressure for cultivated land, droughts and fuelwood collecting is a threat, Acacia senegal is generally well managed as its cultivation is very important. There are a number of pests that may damage it however. The buffalo treehopper ( Stictocephala bubalus ) may destroy seed crops. Spiders ( Cyclops sp.) can smother young growing tips. The larval stages of beetles ( Coleoptera - bruchids), moths and butterflies, and bees and wasps ( Hymenoptera ) can damage the seeds. Locusts ( Acridium melanorhodon ) can defoliate vast areas overnight.

    Acacia senegal is also attacked by the fungi Cladosporium herbarium , Fusarium sp., Ravenelia acaciae-senegalae and R. acaciocola .

    Locusts and browsing goats and camels are major enemies. Herdsmen lopping off branches to make cattle enclosures can also be a threat

    Uses

    The use of gum arabic (or gum acacia), which is derived from an exudate from the bark, dates from the first Egyptian Dynasty (3400 B.C.). It was used in the production of ink, which was made from a mix of carbon, gum and water. Inscriptions from the 18th Dynasty refer to gum as ‘komi’ or ‘komme’. Gum arabic has been used for at least 4,000 years by local people for the preparation of food, in human and veterinary medicine, in crafts, and as a cosmetic. Acacia senegal produces the only acacia gum evaluated toxicologically as a safe food additive.

    Nowadays the gum is present in a wide range of everyday products. 60-75% of the world production of gum arabic is used in the food industry and in human and animal medicine.

    Food 

    In the food industry gum arabic is used as a flavour fixative and emulsifier, to prevent crystallisation of sugar in confectionery, as a stabiliser in frozen dairy products, for its viscosity and adhesive properties in bakery products, and as a foam stabiliser and clouding agent in beer.

    The dried and preserved seeds of  A. senegal  are used as vegetables. The leaves and pods are browsed by sheep, goats, camels, impala and giraffe. The seeds are sometimes eaten as a vegetable in India.

    The flowers are a good source of honey, an important source of nutrition and income generation to support rural livelihoods in marginal lands.

    Medicine

    In pharmaceuticals, it is used as a stabiliser for emulsions, a binder and coating for tablets, and as an ingredient in cough drops and syrups. A soothing and softening agent, gum arabic is extensively employed in folk medicines. Among many other uses, it is used internally for coughs, diarrhoea, dysentery, haemorrhage, and externally to cover inflamed areas.

    Cosmetics

    Gum arabic is used in cosmetics as an adhesive for face masks and powders, and to give a smooth feel to lotions.

    Fuel

    Acacia senegal wood is locally valued for fuel wood and charcoal, although biomass yield per unit of land area is not sufficient to plant it for this.

    Construction

    Industrially, gum arabic is applied as an adhesive, as a protective colloid and safeguarding agent for inks, sensitiser for lithographic plates, coating for special papers, sizing agent for cloth to give body to certain fabrics, and coating to prevent metal corrosion. Gum arabic is also used in the manufacture of matches and ceramic pottery.

    In construction the wood is used locally for poles and fence-posts, the light-coloured wood for tool handles and dark heartwood for weaver's shuttles. Strong ropes are made from the bark fibres of the long surface roots. Where the trees are large (for example near the River Niger) they are cut into planks at least 12 cm thick for making canoes for hunting hippopotamuses. The wood is hard and heavy and takes a beautiful polish, with the sapwood being yellowish white and the heartwood nearly black and irregular. The wood is made into throwing-sticks which, in contrast to the Australian boomerang, can be made to fly straight and used for hunting and pageantry.

    Sand dune stabilisation

    Acacia senegal can help prevent desertification, through sand dune stabilisation and by acting as a wind break.

    Millennium Seed Bank: Seed storage

    Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.

    A collection of Acacia senegal seeds is held in Kew’s Millennium Seed Bank based at Wakehurst in West Sussex.

    See Kew's Seed Information Database for further information on Acacia senegal seeds

    Cultivation

    Gum arabic reaches 4 to 7 m tall with a taproot up to 30 m in depth. It grows on sandy soils and requires strong light. It is drought and heat resistant, but sensitive to waterlogging. The tree is able to fix nitrogen from the air.

    When propagating this species by seed it is important to note that the seeds are hard coated and must be scarified (subjected to mechanical abrasion or hot water treatment) before sowing.

    In agroforestry the seed should be harvested before pods have dried for easy collection and to avoid insect attack. Seed is easily extracted by hand. Freshly extracted seed should immediately be dusted with an insecticide. Seed will remain viable for three to four years if kept in opaque, airtight containers. There are 10,000 to 30,000 seeds per kg. Fresh seed requires no pre-treatment if sown immediately after harvest. Seed collected in previous seasons, however, requires pre-treatment to break seed dormancy. Soaking seed in water for 12 to 24 hours gives good results and is simple to apply. Seeds can also be nicked (a small cut made into them).

    Acacia senegal is raised in plant nurseries in polyethylene pots, two to four seeds per pot, thinned to one seedling after four to six weeks. Direct seeding (five to eight seeds in 30 x 30 x 30 cm pits or larger) can also be used. Strict protection from fire and livestock grazing, and efficient control of weed competition during at least the first two years is important for seedling survival. Minimum spacing for block planting is 4 x 4 m. At 10 x 10 m spacing, agricultural intercropping is possible, for example, inter-planting with millet, beans, or groundnuts.

    When trees are near well watered locations, they grow taller but they do not produce any gum. The tree has to be under stress, diseased, ill-nourished and cut off from water before it will produce gum.

    Distribution
    Angola, Burkina Faso, Cameroon, Central African Republic, Ethiopia, Ghana, India, Kenya, Mali, Mozambique, Namibia, Niger, Oman, Rwanda, Somalia, South Africa, Tanzania, Uganda
    Ecology
    Dry savanna (grassland) and Sahel (desert edge), scattered, often in thickets, and sometimes in extensive pure stands.
    Conservation
    None of the four varieties of this species are threatened. Least Concern according to IUCN Red List criteria.
    Hazards

    None. Senegalia senegal produces the only acacia gum evaluated toxicologically as a safe food additive.

    [FWTA]

    Mimosaceae, Hutchinson and Dalziel. Flora of West Tropical Africa 1:2. 1958

    Habit
    Small tree, to 25 ft. high
    Bole
    Short bole grey and fissured
    Bark
    Bark of twigs yellowish, soon peeling
    Flowers
    Flowers cream, in spikes usually longer than the leaves.
    [FTEA]

    Leguminosae, J. B. Gillett, R. M. Polhill & B. Verdcourt. Flora of Tropical East Africa. 1971

    Habit
    Shrub or tree up to 12 m. high; bark grey, scaly, rough.
    Branches
    Young branchlets densely to sparsely pubescent, soon glabrescent.
    Stipules
    Stipules not spinescent.
    Prickles
    Prickles just below nodes, either in threes, up to 7 mm. long, the central one hooked downwards, the laterals ± curved upwards, or else solitary, the laterals being absent.
    Leaves
    Leaves:petiole glandular or not (gland about 0.5–0.75 mm. in diameter); rhachis ± pubescent, glandular between the top 1–5 pairs of pinnae, prickly or not; pinnae (2–)3–6 pairs, 0.5–1.5 (–2.4, very rarely to 4) cm. long; leaflets 8–18 pairs, 1–4(–7) mm. long, 0.5–1.75 mm. wide; linear- to elliptic-oblong, ciliate on margins only or ± hairy on surface, or wholly subglabrous, lateral nerves not visible or sometimes somewhat prominent beneath, apex obtuse to subacute.
    Flowers
    Flowers white or cream, fragrant, sessile, in spikes 2–10 cm. long on peduncles 0.7–2 cm. long, normally produced with the leaves; axis pubescent to glabrous.
    Calyx
    Calyx 2–2.75(–3.5) mm. long, glabrous to somewhat pubescent.
    Corolla
    Corolla 2.75–4 mm. long, exceeding the calyx, 5-lobed, glabrous outside.
    Stamens
    Stamen-filaments 4.5–7 mm. long, free; anthers 0.2–0.25 mm. across, with a caducous gland.
    Ovary
    Ovary glabrous, very shortly stipitate.
    Fruits
    Pods (Fig. 14/17, p. 52) usually grey-brown, sometimes pale or dark brown, dehiscent, densely to sparsely appressed-pubescent to -puberulous, oblong, straight, venose, rounded to acuminate at apex, (3–)4–14 cm. long, (1.3–)2–3.3 cm. wide.
    Seeds
    Seeds ± subcircular-lenticular, 8–12 mm. diam.; central areole small to medium, 2.5–6 × 2.5–5 mm., markedly impressed.
    [FZ]

    Leguminosae, J.P.M. Brenan. Flora Zambesiaca 3:1. 1970

    Habit
    Shrub or tree up to 13 m. high; bark grey to brown or blackish, scaly, rough; young branchlets densely to sparsely pubescent, soon glabrescent.
    Stipules
    Stipules not spinescent.
    Prickles
    Prickles just below the nodes, either in threes, up to 7 mm. long, the central one hooked downwards, the laterals ± curved upwards, or else solitary, the laterals being absent.
    Leaves
    Leaves: petiole glandular or not (gland c. 0·5-0·75 mm. in diam.); rhachis ± pubescent, glandular between the top 1-5 pairs of pinnae, prickly or not; pinnae (2)3-6(12) pairs, 0·5-1·5(2·4, very rarely to 4 or more) cm. long; leaflets 7-25 pairs, 1-4(9) x 0·5-1·75(-3) mm., linear-to elliptic-oblong, ciliate on the margins only or ± hairy on the surface, or wholly subglabrous, lateral nerves not visible or sometimes somewhat prominent beneath, apex obtuse to subacute.
    Flowers
    Flowers white or cream, fragrant, sessile, in spikes 1·5-10 cm. long on peduncles 0·7-2 cm. long, normally produced with the leaves; axis pubescent to glabrous.
    Calyx
    Calyx 2-2·75(3·5) mm. long, glabrous to somewhat pubescent.
    Corolla
    Corolla 2·75-4 mm. long, exceeding the calyx, 5-lobed, glabrous outside.
    Stamens
    Stamen-filaments 4·5-7 mm. long, free; anthers 0·2-0·25 mm., across, with a caducous gland.
    Ovary
    Ovary glabrous, very shortly stipitate.
    Fruits
    Pods usually grey-brown, sometimes pale- or dark-brown, dehiscent, (1·8)4-19 x (1·2)2-3·4 cm., densely to sparsely appressed-pubescent to -puberulous, oblong, straight, venose, rounded to acuminate at the apex.
    Seeds
    Seeds ± subcircular-lenticular, 8-12 mm. in diam.; central areole small to medium, 2·5-6 x 2·5-5 mm., markedly impressed.
    [KSP]
    Use
    Food, medicinal, crafts, cosmetics.
    [UPPd]
    Digestive System Disorders
    A decoction of the bark is drunk to treat diarrhoea and stomach disorders Bark - Medicinal Plants of East Africa. Second edition Root decoction is slightly purgative and is drunk in the case of constipation or stomach ache Roots (incl. Rhizomes etc) - Medicinal Plants of East Africa. Second edition
    Charcoal
    Charcoal. Unspecified plant parts - Useful trees and shrubs of Kenya
    Gums Resins
    Emulsifiers Exudates - Survey of Economic Plants for Arid and Semi-Arid Lands (SEPASAL) database Adhesives - 'Gum arabic' used as a glue. Exudates - Useful trees and shrubs of Kenya
    Gums, Mucilages or Resins
    Exudates - Field guide to trees of Southern Africa 'Gum arabic' used as food stablizer. Exudates - Useful trees and shrubs of Kenya
    Fuelwood
    Firewood. Unspecified plant parts - Useful trees and shrubs of Kenya
    Other Animal Food Type
    Goats - Leaves as fodder for goats. Leaves - Useful trees and shrubs of Kenya Goats - Pods as fodder for goats. Other plant parts - Useful trees and shrubs of Kenya Camels - Pods as fodder for camels. Other plant parts - Useful trees and shrubs of Kenya Camels - Leaves as fodder for camels. Leaves - Useful trees and shrubs of Kenya
    Herbage
    Other Animals - Black Rhino Leaves - Field guide to trees of Southern Africa
    Infections & Infestations
    Root decoction is used for the treatment of gonorrhoea Roots (incl. Rhizomes etc) - Medicinal Plants of East Africa. Second edition
    Erosion Control
    Soil conservation and sand stabilization. Live plant (in situ) - Useful trees and shrubs of Kenya
    Unspecified Medicinal Disorders
    Veterinary medicine. Unspecified plant parts - Useful trees and shrubs of Kenya 'Gum arabic' has pharmaceutical uses. Exudates - Useful trees and shrubs of Kenya

    Images

    Distribution

    Found In:

    Angola, Benin, Botswana, Burkina, Cameroon, Central African Repu, Chad, Eritrea, Ethiopia, Gambia, Ghana, India, Ivory Coast, Kenya, KwaZulu-Natal, Malawi, Mali, Mauritania, Mozambique, Namibia, Niger, Nigeria, Northern Provinces, Oman, Pakistan, Rwanda, Saudi Arabia, Senegal, Somalia, Sudan, Swaziland, Tanzania, Uganda, Yemen, Zambia, Zaïre, Zimbabwe

    Introduced Into:

    Haiti, Leeward Is., Taiwan

    Common Names

    English
    Gum arabic

    Senegalia senegal (L.) Britton appears in other Kew resources:

    First published in N.L.Britton & P.Wilson, Sci. Surv. Porto Rico & Virgin Islands 6: 538 (1930)

    Accepted in:

    • [3] (2012) Smithsonian Contributions to Botany 98: 1-1192

    Literature

    • [1] Darbyshire, I., Kordofani, M., Farag, I., Candiga, R. & Pickering, H. (eds.) (2015) The Plants of Sudan and South Sudan . Kew publishing, Royal Botanic Gardens, Kew
    • [2] (2012) Nelumbo 54: 39-91
    • [4] Kalema, J. & Beentje, H. (2012) Conservation checklist of the trees of Uganda . Kew Publishing, Royal Botanic Gardens, Kew
    • [5] Mannheimer, C.A. & Curtis, B.A. (eds.) (2009) Le Roux and Müller's field guide to the trees and shrubs of Namibia , rev. ed.: 1-525. Macmillan Education Namibia, Windhoek
    • [6] (2008) Strelitzia 22: 1-279. National Botanical Institute, Pretoria
    • [7] Nelson Sutherland, C.H. (2008) Catálogo de las plantes vasculares de Honduras. Espermatofitas . SERNA/Guaymuras, Tegucigalpa, Honduras
    • [8] (2007) Scripta Botanica Belgica 36: 1-220
    • [9] Spicer, N., Barnes, R. & Timberlake, J. (2007). Acacia Handbook. DFID Forestry Research Programme, U.K.
    • [10] de Lourdes Rico-Acre, M. (2007) A checklist and synopsis of American species of Acacia (Leguminosae: Mimosoideae) . CONABIO, México D.F.
    • [11] Akoègninou, A., van der Burg, W.J. & van der Maesen, L.J.G. (eds.) (2006) Flore Analytique du Bénin . Backhuys Publishers
    • [12] Fagg, C. W. & Allison, G. E. (2004). Acacia senegal and the gum arabic trade. FRP (Forestry Research Programme). Oxford Forestry Institute, Department of Plant Sciences.
    • [13] Kumar, S. & Sane, P.V. (2003) Legumes of South Asia. A Checklist . Royal Botanic Gardens, Kew
    • [14] Timberlake, J., Fagg, C. W., Barnes, R. (1999). Field Guide to the Acacias of Zimbabwe. CBC Publishing, Harare.

    • [15] Burkill, H. M. (1995) . The Useful Plants of West Tropical Africa: Vol. 3 Families J-L. Royal Botanic Gardens, Kew.
    • [16] Jones, M. (1991) A checklist of Gambian plants . Michael Jones, The Gambia College
    • [17] Lebrun, J.p., Toutain, B., Gaston, A. & Boudet, G. (1991) Catalogue des Plantes Vasculaires du Burkina Faso . Institut d' Elevage et de Médecine Vétérinaire des Pays Tropicaux, Maisons Alfort
    • [18] Lock, J.M. (1989) Legumes of Africa a check-list . Royal Botanic Gardens, Kew
    • [19] Peyre de Fabregues, B. & Lebrun, J.-P. (1976) Catalogue des Plantes Vascularies du Niger . Institut d' Elevage et de Médecine Vétérinaire des Pays Tropicaux, Maisons Alfort
    • [20] Berhaut, J. (1975) Flore illustrée du Sénégal 4: 1-625. Gouvernement du Sénégal, Ministère du développement rural direction des eaux et forêta, Dakar
    • [21] (1970) Flora Zambesiaca 3(1): 1-153. Royal Botanic Gardens, Kew
    • [22] Guillemin, J. B. A. Icones Lithographicae Plantarum Australasiae Rariorum. Paris (Treuttel et Wurtz), London, Strasbourg.

    Sources

    Kew Names and Taxonomic Backbone
    The International Plant Names Index and World Checklist of Selected Plant Families (2017). Published on the internet at http://www.ipni.org and http://apps.kew.org/wcsp
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