Umbrella Thorn [Acacia tortillis]
The bark has a rough feel and is grey to black in colour. The tree has a combination of one straight thorn with a small hooked thorn alongside. The thorns are thin and grow in pairs. The flowers form in clusters on old wood. The flowers themselves are creamy, white, balls. The pods are a distinctive pale, gold brown colour and are curled and twisted. The leaves are very small giving the umbrella a soft, feathery appearance.
Browsing animals eat the leaves together with the thorns, the latter more easily when young and soft. The older, hardened thorns can be a deterrent to over-browsing. The thorns are sharp and white, with some straight and others hooked. They are arranged singly or in pairs. The tree flowers in December (summer) with dense, packed white florets, but the flowering can be sporadic depending upon rain.
It has the classic, umbrella-shaped canopy associated with thorn trees. It reaches heights of between 5-20 m in nature. Many bird species take advantage of this protection and build their nests in the canopy. It is fairly slow growing and reaches a final height of between 3-5 m with a spread of 8-13 m.
Flowers and Fruit
Acacia tortilis (Umbrella Thorn) produces a large number of pods that are eaten by wild and domestic animals, and sometimes by man. The pods are tightly coiled spirals, pale brown and fall to the ground unopened. They accumulate in large numbers and are eaten with relish by such animals as Kudu, Impala, Rhino and Elephant.
This is the manner in which the seeds of the unopened pod are dispersed for propagation and better germination after passing through an animal's stomach. The pods of some other acacia trees split before falling to the ground, thus dispersing the seeds by scattering.
The timber is used for fenceposts, firewood, furniture, and wagonwheels. The prolific pods make good fodder for desert grazers and the foliage is also palatable, being one of the major dry season fodder trees for the Sahara-Sahelian belt. The bark is used for string in Tanganyika. Gum from the tree is edible and is used as a poor man's gum. It is the tree most recommended for reclaiming dunes in India and Africa.
The thorny branches are used to erect temporary cages and pens. Bark said to be a good source of tannin. Africans once strung the pods into necklaces. Senegalese use the roots for spear shafts, Lake Chad natives use the stems for fish spears. African nomads often use the flexible roots for frameworks of their temporary shelters. The pods and leaves are high in nutrition and are browsed by game and livestock. Vervet Monkeys and Baboons eat young green pods; other animals eat the pods which fall to the ground.
Acacia tortilis occurs from sand dunes and rocky scarps to alluvial valley bottoms, avoiding seasonally waterlogged sites. A very drought resistant species, the umbrella thorn grows in areas with annual rainfall as low as 40 mm and as much as 1200 mm, with dry seasons of 1-12 months. The tree favors alkaline soils but will colonize saline and gypseous soils.
Where they are found
The Umbrella Thorn is one of the most widely distributed Acacia's. This tree can be found in Mozambique, Botswana, Swaziland, Tranvaal, Orange Free State and the Cape. The tree has been described in Egypt and Arabia 200 years ago. It is said that stands of this tree show areas of good soil and good grasses.