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The camel thorn tree.


Here's a question: If an Acacia erioloba falls in the forest and there is no one around to hear it, does it make any sound? The answer in this case is 'No". But more on that later.

African acacias--the type specimen of the genus Acacia having been an example of Acacia nilotica from Egypt, first described in 1754--have played a significant role in the culture and economy of Africa since the get-go. The generic name comes from the Greek "akis", which means a sharp point. And those of us familiar with the African bush know all about those sharp points!

Acacias are leguminous plants, and like most legumes they form a symbiotic relationship with nitrogen-fixing bacteria on the roots, and are a significant source of atmospheric nitrogen being fixed into the soil for the subsequent use of all maimer of plant species (although some recent research suggests that erioloba, in fact, obtains most of its own nitrogen from the groundwater). Furthermore, they have a close interaction with many animal species; weaver birds nest in them, being afforded protection by the thorns, vultures and eagles use the height to gain good vantage points, and giraffe have adapted to feed largely on acacia trees. Other time-honoured uses are as forage for many species of herbivores--both for the leaves and the pods--wood for construction and fires, and medicinal use for stomach ache, as well as use as emetics, stimulants and aphrodisiacs. It's not clear what, if any, pharmacological properties the plants possess, but they do have a high concentration of tannins in the bark and roots, and the astringent properties of these may be of some use.

One of the most majestic of all the acacias is the Camel Thom, or Giraffe Thom, tree, which was formerly quite happy under in the name of Acacia erioloba. The Camel Thom is a large, spreading acacia, some 8-18 metres in height, which makes it one of Southern Africa's largest species. It is typically found in the sandy Kalahari soils of western Zimbabwe. It is difficult to mistake the Camel Thom for any of its relatives; its characteristic thorns are paired at the nodes, and the leaves are 2-5cm in width and bearing rows of 2-5 pinnae.

Common in Hwange National Park, the Camel Thom ranges from southern Angola and Namibia, across Botswana and into southwest Zambia. It is found in the north and west of South Africa, and just barely into southwestern Mozambique. Rarely growing in deep sand, the Camel Thom is found in shallow sands, often bordering on pans and vleis. Because of its interaction with other species, plant and animal, it is a true keystone species.

The Camel Thom was first the Giraffe Thom, having initially been described and named Acacia giraffae in 1808. But with the genus still being poorly understood at the beginning of the nineteenth century, the type specimen from the northern Cape was discovered by Ross in 1975 to have been a hybrid, one parent being Acacia haematoxylon. Herbarium collections were canvassed anew and the crown passed to a "new" type specimen, which had been named Acacia erioloba in 1836. Ross had suggested back in 1973 that A. erioloba, A. farnesiana (which was probably introduced into Africa), and A. coven, a South American species, were "taxonomically aberrant" enough from other Acacias that he suggested should belong to the genus Vachellia.

Camel Thom wood is dense and heavy, and is often used for firewood and some construction, such as poles for hut and fence building. It is resistant to the effects of fungi and borers like termites, but it will split as it dries.

Perhaps its most significant use is forage for browsers. The pods, which can contain as much as 20% protein, are eaten by elephant, eland and kudu, and are also used to feed domestic livestock like cattle. One large, free-standing Camel Thom at Umguza near Bulawayo has produced 500kg of pods in a year, and a hectare of Camel Thoms can yield between one and two tons of pods per year. Larvae of the Emperor moth (Gynanisa maja)--which are occasionally a human food source in Africa--feed on the foliage, as do wildlife and domestic animals.






No one knows how long these Kalahari giants can live, but estimates range from 100 to 300 years.

So, back to the Acacia erioloba falling in the forest. It can make no sound, because it no longer exists; it is bizarrely significant that a species which is impervious to fungi and insect parasites and can live for perhaps a third of a millennium should fall prey to an even more insidious bane: the modern taxonomist.

In 2013, to use the correct jargon, "retypification of the genus Acacia with the Australian A. penninervis was achieved ... with the aim of determining the placement of the African species in the new generic system". Acacia penninervis is the Australian hickory wattle, the type specimen of which was described in 1825. Acacia nilotica was described in 1754, so, because the International Code of Nomenclature stipulates that if a genus is determined to be polyphyletic, e.g. that it is descended from more than one evolutionary ancestor, the original generic name will follow the type specimen. No worries, then. Africa gets the acacias and Australia can have whatever else as soon as they make up a name for it.

But, in a sleight of hand move in the best traditions of African politics, the Aussies managed to get the 17th Annual International Botanical Congress to change the type species from A. nilotica to A. penninervis

and Africa was left with what a lot of naturalists considered an also-ran, the new genus Vachellia. It's not clear what became of the 71-year time-line lead that nilotica held over penninervis, but even die most staid of Africa's ivy-covered professors were mortified. The War of the Botanists spilled out onto the front pages of newspapers, even to the point of accusing a developed country of usurping the genus at "the expense of widespread changes across numerous developing countries that could least afford the costs of such name changes". And no, this is not made up. So, now, only a Vachellia erioloba can make a noise if it falls in the forest.

Call it what you will, the Camel Thom tree is about as iconic of southern Africa as the Big Five, so the next time you find yourself in its shade, don't fail to appreciate that you are in the presence of greatness.
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Title Annotation:African Perspectives: The Dark Continent in Discussion
Publication:African Hunter Magazine
Date:Jun 1, 2016
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