Introduction

Acacia, sensu lato, is a large and cosmopolitan genus containing some 1350 described species (Ebinger et al., 2000; Orchard and Wilson, 2001; Maslin et al., 2003; Orchard and Maslin, 2003; www.worldwidewattle.com). This genus is associated in particular with savannas and open woodlands in the tropical, subtropical and warm temperate parts of the world. The highest number of species occurs in Australia, followed by the Americas and Africa, and to a lesser extent in Asia (Ross, 1981; Maslin, 2001). They are also found in parts of Indonesia and islands in the Pacific and Indian oceans, and although possibly present in New Zealand millions of years ago, only naturalized Australian species now remain there.

The acacias all belong to the family Mimosaceae. The taxonomy of the genus has been revised several times over the last 30 years, most notably by Vassal (1972) and Pedley (1978, 1986), and more recently by Seigler and Ebinger (2005) and Seigler et al. (2006). The genus was formally described in 1754, being based on the African species Acacia nilotica (Linn.). The word “acacia” was derived from the Greek word akis meaning “sharp point,” referring to the spiny stipules which are characteristic of A. nilotica. Historically their classification was based on morphological characteristics of the inflorescences and foliage; however, more recent descriptions consider chemical, pollen, seed, and germination traits (Evans et al., 1977; New, 1984).

The genus currently comprises three subgenera, Acacia, Aculeiferum, and Phyllodineae, each differing substantially in their geographic distributions and biological characteristics.