Tree may reach 14m high. Short, paired thorns are curved. Leaves are bipinnate. Small creamy to yellowish, actinomorphic Flowers are in spikes with exserted stamens. Fruit: a flat pod with compressed Seeds.
Acacia caffra, Senegalia caffra, Mimosa caffra, Acacia fallax, Acacia multijuga
RSA Tree No. 162.
Common names: Common Hook-thorn, Cat thorn, Wag-‘n-bietjie, White Thorn.
Family: Fabaceae or Leguminosae (Pea, bean or legume family). After the Orchidaceae and the Asteraceae, the Fabaceae is the third largest Angiosperm (flowering plants) family with 700+ genera and close to 20 000 species. Local genera include Acacia (Vauchellia, Senegalia), Albizia, Bauhinia, Bolusanthus, Burkea, Calpurnia, Colophospermum, Cyclopia, Erythrina, Erythrophleum, Faidherbia, Indigofera, Philenoptera and Schotia. The Fabaceae are recognisable by their fruit and by their pinnately compound Leaves. Leaves may also be simple and usually have stipules – some of which may be spinescent. Leaflets are usually entire. Flowers are bisexual and bracteate. Regular flowers usually have 4-5 sepals and the same number of petals. Irregular flowers have 4-5 sepals and 5 or less petals. Stamens have anthers that have 2 pollen sacs and there are usually at least twice the number of stamens as petals – often 10. The superior Ovary has one locule that may contain 1 or more ovules. The Stigma and Style are simple. The single carpel develops into the Fruit, which is usually a pod. The pod dehisces on both sides and may break into segments. Seeds vary.
Name derivation: Acacia – typically thorny. Senegalia – from Senegal. These plant usually do not have spinescent stipules. caffra – from the Cape.
Conservation Status: L C. (Least Concern). 2009 (Raimondo et al.).
The usually fast growing Tree is up to 14m high with a roundish spreading crown. In harsh environments, it may remain a bushy shrub. The Trunk is often twisted. It ends in a spreading, partially branched often-rounded crown. The Bark is brown to blackish and vertical fissures may be present. The small recurved or almost straight Thorns are up to 9mm long and end in a sharp tip. They are grey brown to black and occur in pairs just below the nodes. Older branches often have less or no thorns.
This deciduous tree may be one of the first to produce new Leaves in spring. These new Leaves are bright green and this The large drooping leaves are up to 23cm long and are bipinnate (compound: twice pinnate. The central axis or rachis has lateral “branches” not leaflets and the leaflets are on these “side branches”). They have up to 26 pairs of lateral pinnae (sub-divisions) – each of which has up to 50 pairs of Leaflets (usually less). These leaflets are jugate (having leaflets in pairs) and they may, or not, be hairy. The Petiole (leaf stalk) is up to 3cm long and grooved on the upper surface. A small gland sits on top of the groove more than half way up the petiole. The groove extends up the rachis (axis bearing the leaflets). Additional glands are usually found on the groove between the first 4 pairs of pinna. Petiolules (base of leaflets) are very short. Lateral veins are prominent on the lower surface of the leaflet. Stipules (basal appendages of the petiole) are not spinescent and fall early.
The creamy to yellowish white Flowers occur in hanging Spikes (simple indeterminate inflorescence with sessile flowers on a single unbranched stalk). These spikes are up to 13cm long and usually many of them emerge from leaf axils. Flowers have a strong perfume and are one of the first trees to flower in spring. The Calyx is up to 3mm long and the initially greenish–yellow buds turn reddish later. The Corolla is up to 3,5mm long and has 4 united Petals. The many relatively long Stamens have free Filaments and are clearly white, becoming yellowish with age. They are distinctly exserted (sticking out; projecting beyond, as stamens from a perianth) and provide the white colour to the flowers. There is a single Pistil (a unit of the Gynoecium, the female element of the flower, composed of the Ovary, Style and Stigma). Here the superior Ovary has a single locule. A small filiform (thread or filament like) Style is present. This style elongates and extends the single terminal Stigma beyond the now old stamens. This delayed development helps to ensure cross-pollination. (Sep-Nov).
The long, velvety, flat, pale or dark brown Fruit is a dehiscent Pod. It is up to 19 x 1,5cm and may be straight or sickle shaped. The compressed Seeds are up to 12 x 8mm. Seeds may be damaged by parasitic insects (photo 579). (Dec-Mar). Open pods may remain on the tree for some time.
Distribution & Ecology
Distribution and ecology: Older trees are resistant to fires, drought and frost. Growth rate is between 0,5 and 1m per year. The tree naturally grow in woodlands, along rivers and between grassland and forests including coastal scrub up to an altitude of about 1 500m. They also grow occur amongst boulders and termite mounds. Trees occur in pockets round the Western Cape but are more common from Port Elizabeth, up the East Coast into KwaZulu-Natal, Gauteng, Limpopo, Mpumalanga, North West, Swaziland, Mozambique, Botswana, Zimbabwe and Botswana. Flower Perfume attracts bees. The butterfly larvae Van Son’s Playboy (Deudorix vansoni) feed on the Leaves. The larvae of the butterfly – Pennington’s Playboy (Deudorix penningtoni) may cause stem galls on the Twigs.
The close grained and dense Wood has a dark heartwood and lighter sapwood. It is used for fence posts, making baskets and for fuel. The sapwood is not termite resistant. Leaves and Pods may be poisonous but are grazed by stock. This tree is frost and drought resistant. A number of biggish trees survive because the twisted nature of the wood makes it unsuitable for planks. Xhosa women make use wood from the Roots for making smoking pipes. The Roots can be invasive. It is not a great shade tree and, as a result, allows plants including grass to grow close to the trunk. It is a good tree to grow as a Bonsai.
Boon, R. 2010. Pooley’s Trees of eastern South Africa. Flora and Fauna Publications Trust, Durban.
Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of Southern Africa, edn 3. Struik, Cape Town.
Lawrence, G. H. M, 1951. Taxonomy of Vascular Plants, The Macmillan Company, New York. Tenth Printing 1965.
Palmer, E. & Pitman, N. 1972. Trees of southern Africa, Balkema, Amsterdam, Cape Town.
Ross, J. H. A conspectus of the African Acacia Species. 1979. Botanical Research Institute.
Schmidt, S. Lotter, M. & McCleland, W. 2002. Trees and Shrubs of Mpumalanga and the Kruger National Park.
van Wyk, B. & van Wyk, P. 1997 Field guide to Trees of Southern Africa, Struik, Cape Town.