General Info

Tree to 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.

Description

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 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. 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.

Tree

This 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.

Leaves

The bipinnate (compound: twice pinnate.  The central axis or rachis has lateral “branches” not leaflets and the leaflets are on these “side branches”).  These Leaves are noticeably concentrated towards the ends of branches.  They have up to 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 distinct 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.

Flowers

The tiny sweetly scented Flowers develop in the trees after about 10 years.  They are contained in attractive 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 (photo 122) and not in panicles at the ends of the branches as in Vachellia (Acacia) karroo.  The Calyx is up to 2,5mm long and is campanulate (bell-shaped).  The Corolla has 4 small petals 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 (photos 226).  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 single small terminal Stigma and filiform (thread or filament like) Style is present.  Pollination is enhanced by the flower nectar, which attracts honeybees. (Jul-Nov).

 

Fruit

The relatively large and very distinctive Fruit is a thick, hard Pod.   It is wide but short and often half-moon shaped, almost woody and is indehiscent.  This makes it easy to identify this tree.  The pod is up to 2,5cm thick, 13cm long and 6,5cm wide.  It is externally grey-velutinous (having a hairy surface that is soft and velvety) and spongy within.  These pods may lie on the ground for more than a year before breaking open to release the seeds.  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.  This is different from most acacia.  The horse-shoe shaped marking are visible on the shiny lens-shaped seeds (photo 40).  These seeds are imbedded in the initially spongy tissue.  The dissected pod reveals seeds in more than the typical “one row acacia pod” (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, 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 also 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 forth-deepest roots ever recorded: 60m deep.  This is only 1m less than Juniperus monosperma in the Colorado plateau and a eucalyptus tree in Australia.  The deepest roots ever recorded are those of Boscia albitrunca with a depth of 68m in the Kalahari in Botswana.

Ethnobotany

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 extractable from this plant.  It is astringent and good tasting.  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.  Bushmen to make quivers for their arrows from the Roots.  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).

References

Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of Southern Africa, edn 3. Struik, Cape Town.

Ginn, P.J. McIlleron, W.G. Milstein, S. 1989. The Complete Book of Southern African Birds. Struik Publishers (PTY) LTD. Third impression 1991.

Lawrence, G. H. M, 1951. Taxonomy of Vascular Plants, The Macmillan Company, New York. Tenth Printing 1965.

Ross, J. H. A conspectus of the African Acacia Species. 1979. Botanical Research Institute.

Palmer, E. & Pitman, N. 1972. Trees of southern Africa, Balkema, Amsterdam, Cape Town.

van Wyk, B. & van Wyk, P. 1997 Field guide to Trees of Southern Africa, Struik, Cape Town.

Jennings CMH (1974) The hydrology of Botswana. PhD thesis, University of Natal, South Africa.

 

http://redlist.sanbi.org/species.php?species=15470-5

https://en.wikipedia.org/wiki/Vachellia_erioloba

http://plantzafrica.com/plantab/acaciaeriol.htm

http://jacanaent.com/Library/Trees/CamelThorn.htm

http://tropical.theferns.info/viewtropical.php?id=Vachellia+erioloba

http://posa.sanbi.org/flora/browse.php?src=SP

https://en.wikipedia.org/wiki/Root