The genus Acacia Mill. consists of more than 750 species of shrubs and trees (Willis, 1966) found throughout much of the tropical, sub-tropical and warm temperate zones of the world. It is usually divided into two main sections, the Bipinnatae and the Phyllodineae. Species in the former section possess bipinnate leaves throughout their entire life-span, and are found on the Australian, African, Indian and North American continents.
In the Phyllodineae the rachis of the bipinnate leaf expands vertically to form the adult foliage of phyllodes. Some examples of transitional stages between these two foliage forms are shown in Fig. 1.1. With the exception of a few species on islands in the Indian and Pacific Oceans, the Phyllodineae is confined to Australia. (From Introduction)