DISTRIBUTION

Global | In Australia |

Acacias are associated mostly with subhumid savannas and open woodlands in the subtropical and arid regions of the world. Of the more than 1500 species, they occur in Africa (more than 130 species), Madagascar (c. 100 species), the Americas (c. 270 species), Australia (more than 960 species) and to a lesser extent, in India (c. 18 species). They are also found (in small numbers) in parts of Indonesia and in some of the islands of the Pacific and Indian oceans.

In New Zealand they occur only as naturalised species, having become extinct there possibly some millions of years ago as evidenced by the fossil record.

Fig. 3. The global distribution of Acacia

Many of the African and American Acacia species are heavily armoured with large stipular spines. In some of the Central American species in particular, the base of these spines is enlarged and hollow and is home to, often very aggressive, ants. Known as myrmecophytic plants, they provides the ants with nectar, and in some cases, food in the form of Beltian bodies - small appendices at the apex of the pinnules. It is usually assumed that in return for the food, the ants provide protection to the plant from herbivoures and grazing animals. It has been suggested³³ that the coevolution between the ants and the myrmecophytes in Africa, Asia and the Americas has been due to the selection pressure of large grazing animals, and that the absence of myrmecophytic acacias in Australia is due to the absence of large herbivoures. However, the fossil record indicates³⁴ that Australia was well endowed with large vertebrate herbivoures until relatively recently.

Global | In Australia | The Acacia Community | South-eastern Australia | Diversity