Sunday 2 January 2011

Thorny Acacias

There are some 1200 different species of Acacia distributed all over the tropics and in warm temparete areas. They are found in Australia, Africa as well as in America and preferently on dry grounds. In Africa they are very important trees and shrubs of the savanna and the low bush steppe. Although the African species all are more or less thorny their leaves are still eaten by many animals. The giraffa has specilaized in feeding on Acacia species and with its long and flexible tongue it can avoid the thorns rather well.

The Whistling Acacia, Acacia drepanolobium, is a common small shrub of the East African dry savannas and steppes. It wears long whitish spines and is adorned with dark galls in the size of brussel sprout heads. The galls are hollow inside and have several small openings in the surface. They are found all over the branches. The hollow insides are inhabited by aggressive ants of the genus Crematogaster, a world wide genus sometimes called acrobat ants. The ants form a mutually beneficial partnership together with the acacia as the insects protect the plant against browsing animals by very unpleasant bites on lips and tongue, while the shrub provides housing for the ants inside the galls.

The Flat Topped Acacia, Acacia tortilis, is an abundant, extremely drought tolerant tree from grasslands and savannas in East Africa. It is a medium size tree with a height of about 15 m and has small white aromatic smelling flowers in dense clusters. The Flat Topped Acacia is an important source for shade for resting mammals and the leaves and buds are eaten by many animals. It is also used as firewood and for charcoal production by the local people.

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