Tree may reach 9m high with many short, curved, vicious thorns. Leaves are bipinnate with non-spinescent stipules. The creamy-white Flower colour is due to many exserted stamens. Fruit: pod with up to 3 seeds.
Acacia mellifera, Senegalia mellifera subsp. detinens, Acacia detinens, Acacia tenax
RSA Tree No. 176, 176.1
Common names: Black thorn, Beira-boom, Hook Thorn, Blouhaak, Swarthaak, Black-thorned acacia.
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 Tree genera include Acacia (Vauchellia, Senegalia), Albizia, Bauhinia, Bolusanthus, Burkea, Calpurnia, Colophospermum, Cyclopia, Dichrostachys, Erythrina, Erythrophleum, Faidherbia, Indigofera, Mundulea, Peltophorum, Philenoptera, Schotia and Xanthocercis. 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. This pod dehisces on both sides and may break into segments. Seeds vary.
Name derivation: Acacia – typically thorny. Senegalia – from Senegal. These plants usually do not have spinescent stipules. mellifera – sweet honey-bearing (blossoms). subsp. detinens – referring to the many, paired, vicious, curved thorns that holds one fast.
Conservation Status: L. C. Least Concern: 2015.
This single stemmed Tree may be up to 9m high. It can also be a multi-stemmed obconical (resembles an inverted cone) shrub. The Crown is approximately spherical. Young Branches are olive brown or reddish to greyish brown and have clearly visible, pale lenticels (a usually raised corky oval or elongated area on the plant that allows the interchange of gases with the environment – photo 884). Branches tend to develop close to the ground. The Trunk remains greyish brown or become purplish black and longitudinally fissured. The blackish Prickles (a short-pointed outgrowth on the bark or epidermis of a plant; a small thorn) occur in pairs below each node. They curve towards the trunk. Prickles are 2,5-6mm long and are very numerous – more so than in other Acacia species. They are often almost parallel to each other. Single curved thorns may occur on the trunk and old branches (photo 884 & 882). This is one of the few “acacias” to have hooked thorns and a ball shaped inflorescence.
The Leaves are bipinnate (compound: twice pinnate. The central axis or rachis has lateral “branches” not leaflets and the leaflets are on these “side branches” or pinna). There is usually a gland present on the upper surface of the short (up to 1,2cm long) hairy Petiole (leaf stalk). Young leaves are bright green but become dull greyish-green with time. The petiole and rachis may be glabrous or pubescent. The length of the leaf Rachis (main axis) varies between 0,2 and 4cm long. Up to 3 pairs of Pinnae are usually present and a there may be a gland at the base of the 1-2 pinnae pairs. Up to 3 pairs of large, blue-green Leaflets are present. The asymmetric leaflets are either single or in pairs but seldom in threes. Veins are visible on both sides of the relatively large leaflets – up to 15 x 12mm. The Stipules (basal appendage of the petiole) are not spinescent and are soon lost. Leaves are usually shed after the first frost.
The sweet-scented, creamy white to yellowish-white Flowers open before the leaves appear. Occasionally the flowers may be pink. In the first the photo below the new leaves are beginning to appear. The buds may have a purplish or pinkish tinge. Flowers occur in very short Spikes (simple indeterminate inflorescence with sessile flowers on a single unbranched stalk) and are usually globose. In some cases, the spikes are longer. The Pedicels (stalks of single flowers in a cluster) are relatively short – up to 1,5mm long. The green Calyx is very short and the Corolla is up to 3,5mm long. (Sep-Nov).
The fast developing Fruit occurs in dehiscent papery Pods. Young pods are reddish and mature to a greenish-white, straw coloured or a pale brown colour. They are usually up to 8 x 2,5cm. The pods narrow slightly at both ends. The 2 to 3 Seeds are up to 10 x 8mm and fallen pod may still have attached seeds. (Jan-Apr).
Distribution & Ecology
The trees are located in the northwest of the Northern Cape, Western Free State, Gauteng, North West, Limpopo, Mpumalanga and northwards to include eastern and southern Botswana, north-west and south west Mozambique, Namibia, Tanzania, Sudan and Egypt. They survive in the semi-desert and are common in bushveld areas. They also grow in mixed deciduous woodlands and in brackish flat ground. The tree can spread by coppice growth (cutting or burning stems causes regrowth from the stump or roots) and by seeds. These trees can form impenetrable tangled, thorny growth. This tree it is a valuable for both shade and fodder. The leaves and stems have a high percentage of protein. The Pods are very nutritious and sought after by both game e.g. kudu and livestock. Black rhino, Elephants, Eland, Impala, Kudu, Steenbok and Giraffe, consume the Leaves. Nectar attracts Bush babies and bats and they aid in pollination. Its deep taproot enables it to survive further away from streams and rivers compared to some of its competitors.
The tree provides good shade for stock but this plant may form impenetrable thickets – especially in overgrazed areas. The heartwood is dark brown to greenish-black and makes good furniture and, when oiled, turns black. It is termite resistant and is used for fence posts and hut construction. The sapwood is thick and whitish. Although small, the many Thorns are wicked and an unwary traveller can be caught up in them. Extensive use is made of Wood for fuel and charcoal manufacture. Twigs are chewed. They are also used to clean teeth. Goats consume Leaves. The leaves contains DMT – a hallucinogenic drug. The Gum is edible. It may be mixed with clay to make floors. Soaking seeds in hot water in the morning and planting them the following day can be enhanced germination. Growth is about 0,5m per year. Best growth occurs in deep sandy soil in frost-restricted areas.
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Ross, J. H. A conspectus of the African Acacia Species. 1979. Botanical Research Institute.
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