Acacia gerrardii (PROTA)

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Plant Resources of Tropical Africa
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Acacia gerrardii Benth.


Protologue: Trans. Linn. Soc. London 30(3): 508 (1875).
Family: Mimosaceae (Leguminosae - Mimosoideae)
Chromosome number: 2n = 52

Synonyms

  • Acacia hebecladoides Harms (1902).

Vernacular names

  • Grey-haired acacia, red-thorn (En).

Origin and geographic distribution

Acacia gerrardii is distributed from Benin eastwards to Ethiopia and from there southwards to South Africa. A second subspecies is distributed in Israel, Iraq, Jordan and the Arabian Peninsula.

Uses

The bark is used for making rope and twine. In Kenya the leaves and pods are eaten by livestock, in Zimbabwe goats browse the leaves. From West Africa, however, it is reported that cattle rarely consume the foliage. Acacia gerrardii is considered a useful tree in grazing land as it provides only light shade and does not depress growth of the fodder species beneath. In Uganda trees are spared during land clearance for farming or for rangeland. In Zimbabwe it was found to be suitable to stabilize and reclaim mine waste and ash. In Kenya the thorny branches are used to make fences for livestock enclosures (‘bomas’). The wood is used as timber, for carvings, small furniture, poles, posts, tool handles, for charcoal production, and as fuelwood. A soup is made from the bark. Honey bees feed on the flowers. In arid regions of the United States the species is promoted as an ornamental in desert landscape designs.

The inner part of the bark is used either by chewing or in hot water to treat coughs and sore throat. The bark is emetic and used to treat diarrhoea in children. To relieve stomach-pain in Tanzania the root is pounded and taken with hot water, while in Sudan the leaves are used for the same purpose. The pounded and cooked root is mixed with porridge and eaten 3 times per day to cure schistosomiasis. In Sudan the bark and pods are used to kill snails.

Properties

The sapwood is creamy brown and is not clearly demarcated from the heartwood, although the latter is tinged pink. The texture is medium to coarse. The wood is fairly hard and moderately heavy, with a density of c. 900 kg/m³. The wood is prone to splitting and fungal staining and is moderately resistant to borers and termites. It needs careful seasoning.

The leaves contain over 17% crude protein. Acetone extracts of the bark have yielded (+)-catechin galloyl esters. Ethyl acetate extracts of Acacia species were found to kill snails. The gum is water soluble and contains 43% arabinose, 40% galactose, 1% rhamnose, 9% 4-methyl-glucuronic acid and 7% glucuronic acid.

Description

Tree up to 10(–15) m tall, less frequent a shrub; root system deep; trunk 20–30 cm in diameter; bark rough and fissured, grey to blackish brown or black; twigs grey-brown hairy or glabrous; crown flat, umbrella-shaped or irregular, usually narrow and open; branchlets with paired, grey, stipular spines usually up to 1.5 cm long, rarely up to 6 cm long, straight or hooked or recurved. Leaves alternate, bipinnately compound, with (3–)5–10(–12) pairs of pinnae; petiole 0.5–2.5 cm long; rachis (1.5–)2–7 cm long; leaflets usually in 12–28 pairs per pinna, 3–7.5 mm × 1–2 mm, hairy at least on margins near the base. Inflorescence an axillary, globose head, 1–several per leaf axil, with a pair of small bracts in basal half of peduncle; head c. 50-flowered. Flowers 4–6-merous, white or cream, scented; corolla glabrous or only slightly pubescent; stamens numerous, free, anthers glandular, at least some; ovary superior, 1-celled, style long and slender. Fruit a linear-oblong to linear, flattened pod, 4–22 cm × 6–11(–17) mm, curved or rarely straight, valves thin, velvety or glabrous. Seeds almost square in outline, flattened, 9–12 mm × 7 mm, olive-brown. Seedling with epigeal germination.

Other botanical information

Acacia is a large pantropical genus, comprising more than 1300 species; most of them are found in Australia (more than 900), more than 200 in America, and about 130 in Africa. Acacia gerrardii belongs to subgenus Acacia, which accommodates all the African Acacia species with straight spinescent stipules. Acacia gerrardii subsp. negevensis Zohary is found in Israel, Iraq, Jordan and the Arabian peninsula. In subspecies gerrardii 3 varieties (var. gerrardii, var. latisiliqua Brenan and var. calvescens Brenan) have been distinguished, based on hairiness of young branches, width of the pods and the shape of the spines. However, in Kenya, where all 3 varieties occur, the distinction between them is not felt to be meaningful, because various intermediate forms exist.

Acacia ancistroclada Brenan is a shrub or small tree up to 7.5 m tall, only occurring in southern Kenya and northern Tanzania. In Kenya the bark is used to make string. Acacia luederitzii Engl. (‘false umbrella thorn’) is a tree up to 12 m tall, with a trunk 15–30(–75) cm in diameter, often branching from the base. It is distributed in Zambia, Namibia, Botswana, Zimbabwe, Mozambique, South Africa and Swaziland. Fibres from the inner bark are used for making cordage.

Growth and development

Growth rates are moderately high where groundwater is available but slow where this is not the case. Flowering takes place just before or at the start of the rains. The species roots moderately deep and has small lateral roots. It nodulates and fixes nitrogen.

Ecology

Acacia gerrardii occurs at 450–2200 m altitude on soils ranging from loamy to clayey, most often in wooded savanna, woodland and occasionally in riverine forest. In East Africa it is sometimes common and dominant. In Zimbabwe it is sometimes found on termite mounds, often as a small, gregarious shrub.

Propagation and planting

Acacia gerrardii is easily propagated by seed. There are 10,000–15,000 seeds per kg. Seeds can be sown in pots or direct at the intended site. Germination is improved by immersing the seed in hot water, allowing it to cool and leaving it to soak for 24 hours. Germination usually takes about 5 days. Seeds can be stored for a long time in a dry place, but they are susceptible to bruchid damage. Ash is added to seeds in storage to reduce infestation and damage.

Management

Planting Acacia gerrardii close to homesteads is not recommended because of the nasty thorns. Trees can be coppiced at any height of the trunk, but the number of shoots is higher when the stump surface is larger. Where Acacia gerrardii needs to be removed, stumps can be dug out or burned, or the cut surface of the stumps can be sprayed with a picloram/2,4-D mixture.

Diseases and pests

In Saudi Arabia Acacia gerrardii subspecies negevensis is classified as susceptible to Meloidogyne javanica. Probably the same is true for the African subspecies.

Harvesting

The bark of Acacia gerrardii is harvested piecemeal and for browse branches are lopped.

Genetic resources

There are 2 accessions stored in the USDA National Plant Germplasm System collections. Efforts have been made to explore, assemble and evaluate genetic resources of 6 African Acacia species and this has resulted in a collection of 141 provenances. Acacia gerrardii was not included but would be a good choice to extend this collection.

Prospects

Acacia gerrardii is not among the most promising species of Acacia but the wide genetic variation within the species and its wide distribution are likely to be a good basis for selection for desirable traits. Analysis of the genetic variation within the Kenyan populations might be worthwhile to understand the level of differentiation between varieties of subspecies gerrardii.

Major references

  • Brenan, J.P.M., 1959. Leguminosae subfamily Mimosoideae. In: Hubbard, C.E. & Milne-Redhead, E. (Editors). Flora of Tropical East Africa. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 173 pp.
  • Burkill, H.M., 1995. The useful plants of West Tropical Africa. 2nd Edition. Volume 3, Families J–L. Royal Botanic Gardens, Kew, Richmond, United Kingdom. 857 pp.
  • Dharani, N., 2002. Field guide to common trees and shrubs of East Africa. Struik Publishers, Cape Town, South Africa. 320 pp.
  • Katende, A.B., Birnie, A. & Tengnäs, B., 1995. Useful trees and shrubs for Uganda: identification, propagation and management for agricultural and pastoral communities. Technical Handbook 10. Regional Soil Conservation Unit, Nairobi, Kenya. 710 pp.
  • Timberlake, J., Fagg, C. & Barnes, R., 1999. Field guide to the Acacias of Zimbabwe. CBC Publishing, Harare, Zimbabwe. 160 pp.

Other references

  • Arbonnier, M., 2000. Arbres, arbustes et lianes des zones sèches d’Afrique de l’Ouest. CIRAD, MNHN, UICN. 541 pp.
  • Ayoub, H.S.M., 1985. Flavanol molluscicides from the Sudan acacias. Pharmaceutical Biology 23(2): 87–90.
  • Beentje, H.J., 1994. Kenya trees, shrubs and lianas. National Museums of Kenya, Nairobi, Kenya. 722 pp.
  • Bingham, M.H., 1990. An ethno-botanical survey of Senanga West. Senanga West Agricultural Development Area, Department of Agriculture, Republic of Zambia. 27 pp.
  • Brenan, J.P.M., 1970. Leguminosae (Mimosoideae). In: Brenan, J.P.M. (Editor). Flora Zambesiaca. Volume 3, part 1. Crown Agents for Oversea Governments and Administrations, London, United Kingdom. 153 pp.
  • Grace, O.M., Prendergast, H.D.V., Jäger, A.K. & van Staden, J., 2002. Bark medicines in traditional healthcare in KwaZulu-Natal, South Africa: an inventory. South African Journal of Botany 69(3): 301–363.
  • Hegnauer, R. & Hegnauer, M., 1996. Chemotaxonomie der Pflanzen. Band 11b-1. Birkhäuser Verlag, Basel, Switzerland. 500 pp.
  • Ibrahim, A.A.M. & Aref, I.M., 2000. Host status of thirteen Acacia species to Meloidogyne javanica. Journal of Nematology 32(4S): 609–613.
  • Jurasek, P., Kosik, M. & Phillips, G.O., 1993. A chemometric study of the Acacia (gum arabic) and related natural gums. Food Hydrocolloids 7(1): 73–85.
  • Mahmoud, M.A., Khidir, M.O., Khalifa, M.A., Bashir el Amadi, A.M., Musnad, H.A.R. & Mohamed, E.T.I., 1995. Sudan: Country Report to the FAO International Technical Conference on Plant Genetic Resources (Leipzig 1996). Khartoum, Sudan. 86 pp.
  • Malan, E. & Pienaar, D.H., 1987. (+)-catechin-galloyl esters from the bark of Acacia gerrardii. Phytochemistry 26(7): 2049–2051.
  • Maundu, P., Berger, D., Saitabau, C., Nasieku, J., Kipelian, M., Mathenge, S., Morimoto, Y. & Höft, R., 2001. Ethnobotany of the Loita Maasai. Towards community management of the forest of the Lost Child. Experiences from the Loita Ethnobotany Project. UNESCO People and Plants Working Paper 8, Paris, France. 34 pp.
  • Mucunguzi, P., 1995. Effects of bruchid beetles on germination and establishment of Acacia species. African Journal of Ecology 33(1): 64–70.
  • Piha, M.I., Vallack, H.W., Michael, N. & Reeler, B.M., 1995. A low input approach to vegetation establishment on mine and coal ash wastes in semi-arid regions. II. Lagooned pulverized fuel ash in Zimbabwe. Journal of Applied Ecology 32(2): 382–390.
  • Ross, J.H., 1979. A conspectus of the African Acacia species. Memoirs of the Botanical Survey of South Africa No 44. 155 pp.
  • Shackleton, C.M., 2000. Stump size and the number of coppice shoots for selected savanna tree species. South African Journal of Botany 66(2): 124–127.
  • USDA, ARS & National Genetic Resources Program, 2011. Germplasm Resources Information Network - (GRIN). [Internet] National Germplasm Resources Laboratory, Beltsville, Maryland, United States. http://www.ars-grin.gov/. January 2011.
  • van Wyk, B. & van Wyk, P., 1997. Field guide to trees of southern Africa. Struik Publishers, Cape Town, South Africa. 536 pp.

Sources of illustration

  • Katende, A.B., Birnie, A. & Tengnäs, B., 1995. Useful trees and shrubs for Uganda: identification, propagation and management for agricultural and pastoral communities. Technical Handbook 10. Regional Soil Conservation Unit, Nairobi, Kenya. 710 pp.
  • Timberlake, J., Fagg, C. & Barnes, R., 1999. Field guide to the Acacias of Zimbabwe. CBC Publishing, Harare, Zimbabwe. 160 pp.

Author(s)

  • N. Nyunaï, Institut de Recherches Médicales et d’Etudes des Plantes Médicinales, B.P. 3805, Yaoundé, Cameroon

Correct citation of this article

Nyunaï, N., 2011. Acacia gerrardii Benth. [Internet] Record from PROTA4U. Brink, M. & Achigan-Dako, E.G. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, Netherlands. <http://www.prota4u.org/search.asp>.

Accessed 26 November 2017.