Tree may reach in 10+m high. Bipinnate Leaves have spinescent stipules. Tiny actinomorphic Flowers with exserted stamens are in golden yellow spherical spikes. Fruit: distinctive ear-shaped pod.
Acacia erioloba, Vachellia erioloba, Acacia giraffe
RSA Tree No. 168.
Common names: Camel thorn – because giraffe (camel horse: Afrikaans: kameelperd) ate the leaves, kameeldoring, Giraffe Tree, Giraffe 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. Vachellia – named after George H. Vachell (1789 – 1839), chaplain and plant collector in China. These plants have a capitate inflorescence and stipules that are spinescent. erioloba refers to the fruit which is found in the ear-shaped pods.
Conservation Status: L C. (Least Concern). 2015 (L. von Staden & D Raimondo). The use of the wood for fuel may become a problem in the future.
The wide spreading umbrella-shaped or rounded crown on this Tree is usually up to 15m high but is often only 2m high in drier areas. It may also be a shrub. The Trunk has a rough, dark greyish brown to blackish Bark, which may become fissured into long strips and may flake off when old. Young branches are distinctly shiny red to purple to grey and angled between each pair of thorns. Branches may droop or are flattened and spreading.
The bipinnate (compound: twice pinnate. The central axis or rachis has lateral “branches” not leaflets and the leaflets are on these “side branches”) Leaves are densely situated towards the ends of branches. They have 1-5 pairs of hairless pinnae (sub-divisions) – each of which has to 8-18 pairs of Leaflets. Each blue-green leaflet is up to 13 x 4mm and there are spaces between them. Individual leaflets are oblong to narrowly obovate. The end pair may curve outwards. A small gland may be found at the junction of each pair of pinnae and may be difficult to see. Veins are more visible below. The Petiole (leaf stalk) is less than 1,5cm long and a petiolar gland is absent. Stipules (basal appendages of the petiole) are spinescent (having or becoming spiny) and have paired, stout, sharp, white or brownish Thorns that are usually up to 6cm long. They are strong, almost straight, and vicious. They may be swollen or even fused at the base.
The sweetly scented Flowers develop in the trees after about 10 years. They are contained in yellow or golden, capitate (formed like a head) Spikes (simple indeterminate inflorescence with sessile flowers on a single unbranched stalk). Flowers occur in scattered tufts in axils of the leaves and not in panicles at the ends of the branches as in Vachellia (Acacia) karroo (photo 122). The Calyx is up to 2,5mm long and campanulate (bell-shaped). There 4 small petals in the Corolla which is up to 4mm long. The numerous Stamens are exserted (sticking out; projecting beyond, as stamens from a perianth) with free golden filaments and are much longer than both the sepals and petals. They form the most visible part of the flower. There is a single Pistil (a unit of the Gynoecium, the female element of the flower, composed of the Ovary, Style and Stigma) and the superior Ovary has a single locule. A single small terminal Stigma and filiform (thread or filament like) style is present. Pollination is due to the flower nectar, which attracts honeybees. (Jul-Nov).
The relatively large and very distinctive Fruit is a thick, hard and indehiscent woody Pod. It is unusually wide but short and often half-moon shaped. This pod is an easy way to identify the tree. The pod is up to 2,5cm thick, 13cm long and 6,5cm wide. It is grey-velutinous (having a hairy surface that is soft and velvety) externally and spongy within. Mature pods are covered with velvety hairs and are grey coloured. These may lie on the ground for more than a year before breaking open. Youngish pods may be found together with recently opening pods from the previous year (photo 822). The Seeds are up to 14 x 10mm and are unusually scattered in indistinct rows. Seeds, which are lens-shaped, are imbedded in an initially spongy tissue. The dissected pod reveals seeds in more than the typical one row (photo 09).
Distribution & Ecology
This is an impressive Tree in the dry Kalahari (semi-arid savanna in southern Africa) including parts of Free State, Limpopo, North West, Zimbabwe, South West Mozambique, Swaziland, Southern Angola, Botswana e.g. Kgalagadi Transfrontier Park. About a quarter of this park is in the RSA. Trees occur in Namibia, often within visible red sands. In the red sand areas of southern Africa is where the tree is most conspicuous and becomes the dominant tree. Trees usually occur between an altitude of 900 and 1 100m. They are also located in the Richtersveld (mountainous desert landscape near the NW corner of the Northern Cape – here largely dependent on fog for the water supply). Here it is also a dominant tree. Trees are located further East in Sekhukuniland (South Eastern Limpopo and Mpumalanga). Hybrids exist between this tree and Vachellia haematoxylon. Giraffe consume the Leaves and Flowers. They use their long thin tongues to bypass the thorns. Rhino, elephant, gemsbok, and eland consume the Pods. Baboons eat young pods. This is an important shade tree in dry areas. The tree is home to sociable weavers that often build their massive communal nests in the trees. The trees coppices and suckers relatively easily. Like Vachellia karroo, the Roots may penetrate deeply into the soil. Vachellia erioloba has the second deepest roots ever recorded: 60m deep. The deepest roots ever recorded are those of Boscia albitrunca with a depth of 68m in the Kalahari in Botswana.
This is the Royal Tree of southern Botswana. Seeds have been used, after roasting, as a coffee bean substitute. Pods are nutritious and eaten by domestic animals and may increase milk yield. Prussic acid (Hydrogen cyanide) may be present in the pods. Green leaves may also have large quantities of prussic acid and, provided they are eaten slowly, seem to have little effect. The good quality Gum – called Cape Gum, is astringent, good tasting and is extracted from this plant. The Acacia rat (Thallomys paedulcus) consumes the gum, leaves and seeds. Wood. There is a clear distinction between the light sapwood and the much darker, reddish brown heartwood (photo 837). This wood is hard, strong and is resistant to borers and termites. The wood is used as fuel. Roots have been used by the Bushmen to make quivers for their arrows. Growing. Seeds need to be collected from dung or scarified before planting and, once germinated, should be rapidly transplanted because of the long taproot. The tree is slow growing – a maximum of 0,5m per year. Young seedlings need watering thereafter they are drought resistant. This is a street tree in Mokopane (Potgietersrus) in central Limpopo. The tree is a protected in the RSA. Planted trees are used to help in the stabilization of sand dunes and to combat soil erosion.
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