Acacia trees are without a doubt the most iconic trees in Africa (besides baobabs, a close runner-up). They're an icon of the African savanna, but various species of acacias occur in many other warm, tropical, and desert-like regions of the world, too. They are found on the rocky grounds of Africa's grasslands and in areas with annual rainfall as low as 4 cm.
Until recently, they all belonged to the same genus, Acacia. Today botanists have renamed many of the species, grouping them in five separate genera. Acacia trees are not just one species, and there are many species of the Acacia in Africa.
Acacias can be tall trees or low-growing shrubs. Acacia are gnarled. The stem of the tree is used to treat asthma, and diarrhea.
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From my father making a fire for the braai on a Friday night... To me running in the field and stepping into one of those dreaded long thorns. Oh my those were the days.
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The Zoo and Safari Park have long cultivated acacias for their beauty and their shade-and because they are popular browse for many of the hoofed mammals! We grow 38 taxa of acacias and they are one of our accredited plant collections. A knobthorn acacia Senegalia nigrescens stands guard at Safari Base Camp at the Safari Park.
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The African acacia is self-protecting in many ways. First, most species have long, sharp thorns, which prevent (most) animals from eating their leaves. Second, sometimes stinging ants live inside hollowed-out thorns, which provides another disincentive for predators. And furthermore, the trees create poisonous chemicals when they detect an “assault.” Not only can these chemicals be fatal to animals, but the trees “warn” nearby acacias to start making their own poison.
How it works: When the leaves begin to fill with poison, they release ethylene gas, which drifts out of their pores and toward other acacias (within 50 yards).
Key Characteristics and Adaptations
Acacia trees thrive in areas with extreme temperature fluctuations, enduring scorching heat during the day and freezing temperatures at nights. The Umbrella Thorn prevent water loss. This adaptation helps it get the water during the dry spells. Its taproot, which can reach 115 ft under the ground.
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In many varieties from dry areas, though, compound leaves are replaced by flattened leaf stalks, called phyllodes, that look like long, simple leaves. The reduced surface area of a phyllode is an adaptation for conserving water. They are able to absorb large amounts of sunlight with the smallest possible leaves.
People admire the feathery, compound leaves of some acacias; small leaflets are arranged in rows, one on each side a leaf's midrib, and each of those leaflets is further divided in the same fashion. This gives the leaves of these acacias a delicate, fern-like look.
In many acacias, long, sharp thorns hide among the leaves. shorter, hooked thorns that grow alongside each other. While thorns may discourage some predators, they're no match for the talented tongue of a giraffe.
Acacias bloom in clusters of small, yellow or whitish flowers. of flowers that grow on the Acacia. They also produce long and 1 mm wide. pods.
The Vachellia tortilis is widespread in Africa, being found in countries like Tunisia, Morocco, Uganda, Angola, Zimbabwe, Djibouti, and Botswana. In extremely arid conditions, it may occur as a small, wiry bush. In good conditions, it grows up to 21 m (70 ft) in height. The tree carries leaves that grow to approx. 2.5 cm (1 in) in length with between 4 and 10 pair of pinnae each with up to 15 pairs of leaflets. Its most interesting feature is that it has pairs of thorns; one long, straight and pale, the second short, curved and dark.
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The flowers are small and white, highly aromatic, and occur in tight clusters. The plant is known to tolerate high alkalinity, drought, high temperatures, sandy and stony soils, strongly sloped rooting surfaces, and to withstand sandblasting too.
The southern subspecies heteracantha, here seen in flower, is smaller and often without a spreading crown.
Acacia erioloba, known as the giraffe thorn or camel thorn tree, is the most recognizable tree in the Kalahari desert (and elsewhere in Angola, Botswana, Mozambique, Namibia, South Africa, Zambia, and Zimbabwe).
Acacia senegal, found in Sudan and the northern Sahara, is the main source of gum arabic, which has been used for over 2,000 years in paints and watercolors.
Acacia trees are not endangered, and it is actually plentiful.
Amazing Symbiosis: Ant Army Defends Tree | National Geographic
Native to the savannas of Africa and commonly found in the Serengeti, the whistling thorn tree Vachellia drepanolobium is a tall (up to 18 feet), swollen-thorn acacia. Adorned with small white flowers, the whistling thorn sports leaves comprised of tiny leaflets, as well as seed pods and, most notably, three-inch-long spikes on its branches.
As with other African acacias, these thorns serve as protection from the hungry mouths of herbivores like giraffes and elephants.
Symbiotic Relationships
Within the swollen thorn bulbs of the whistling thorn tree, four ant species- Crematogaster nigriceps, C. mimosae, C. sjostedti, and Tetraponera penzigi-have made themselves right at home. They bore holes into the bulbs and settle in, enjoying shelter and the nectar the trees provide. In exchange, the ants have access to the tree’s nectar, and a safe place to live. It’s a win-win situation, notes Adam Graves, director of horticulture at the San Diego Zoo.
When the wind blows, the spiky appendages become natural whistles, resulting in the sound that gives the tree its common name. But the ants aren’t just providing a soundtrack to the tree’s life; they defend the whistling thorn against tree-grazing mammals. This home security system is crucial, because, unlike other acacia trees, the whistling thorn tree doesn’t have toxic chemicals that would keep snackers at bay.
“The way these organisms have evolved to help each other survive shows firsthand the amazing symbiotic relationships that can evolve in nature,” Adam explains.
Come see-and perhaps hear-for yourself.
Whistling Thorn Tree
Uses and Economic Importance
Examine the ingredients list of your favorite gum, candy, or soft drink, and you might see the term "gum arabic." This water-soluble emulsifier and stabilizer comes from the hardened sap of various African acacias, and it's just one of the many products we get from acacias.
Its hardy, termite-proof wood can be used to make tool handles and fencing, or for kindling; and the gum is sometimes collected for use as glue.
The pods and foliage, which grow prolifically on the tree, are used as fodder for desert grazing animals. The bark is often used as a string medium in Tanzania, and is a source for tannin. Gum from the tree is edible and can be used as gum arabic.
Timber from the tree is used for furniture, wagon wheels, fence posts, cages, and pens.
Acacias are fast growing, so they are often planted for land rehabilitation. Acacias provide a good source of honey in some regions. The leaves, flowers, and seedpods. shade for the animals of the savanna. makes very good charcoal and firewood.
We also use them to protect the gardens at home by placing them in between the plants so that the dogs won't mess up the garden.
| Species | Common Name | Uses |
|---|---|---|
| Vachellia drepanolobium | Whistling Thorn Tree | Shelter for ants, protection against herbivores |
| Acacia senegal | Gum Arabic Tree | Source of gum arabic for paints, watercolors, and food products |
| Acacia erioloba | Giraffe Thorn/Camel Thorn Tree | Fodder for animals, shade |
by Patricia N. All commercial rights reserved.
