Acacia

Acacia, commonly known as wattles or acacias, is a genus of about 1,084 species of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa, South America, and Australasia, but is now reserved for species mainly from Australia, with others from New Guinea, Southeast Asia, and the Indian Ocean. The genus name is Neo-Latin, borrowed from Koine Greek ἀκακία (akakia), a term used in antiquity to describe a preparation extracted from Vachellia nilotica, the original type species.

Several species of Acacia have been introduced to various parts of the world, and two million hectares of commercial plantations have been established.

Plants in the genus Acacia are shrubs or trees with bipinnate leaves, the mature leaves sometimes reduced to phyllodes or rarely absent. There are 2 small stipules at the base of the leaf, but sometimes fall off as the leaf matures. The flowers are borne in spikes or cylindrical heads, sometimes singly, in pairs or in racemes in the axils of leaves or phyllodes, sometimes in panicles on the ends of branches. Each spike or cylindrical head has many small golden-yellow to pale creamy-white flowers, each with 4 or 5 sepals and petals, more than 10 stamens, and a thread-like style that is longer than the stamens. The fruit is a variably-shaped pod, sometimes flat or cylindrical, containing seeds with a fleshy aril on the end.

The genus was first validly named in 1754 by Philip Miller in The Gardeners Dictionary. In 1913 Nathaniel Lord Britton and Addison Brown selected Mimosa scorpioides L. (≡ Acacia scorpioides (L.) W.Wight = Acacia nilotica (L.) Delille), a species from Africa, as the lectotype of the name.

The genus name comes from Neo-Latin; Gaspard Bauhin in his book Pinax (1623) writes it coming from Dioscorides; the Koine term ἀκακία akakía is the name he uses for Vachellia nilotica, the original type species growing in Roman Egypt, from ἀκακίς akakis meaning "point".

The origin of "wattle" may be an proto-Germanic word meaning "to weave". First attested about 700, Old English: watul referred to the flexible woody vines, branches, and sticks which were interwoven to form walls, roofs, and fences. Since about 1810, it has been used as the common name for the Australian legume trees and shrubs such as Acacia species proper, Castanospermum australe, and Sesbania species that can provide these branches.

The genus Acacia was considered to contain some 1352 species leading to 1986. That year, Leslie Pedley questioned the monophyletic nature of the genus, and proposed a split into three genera: Acacia sensu stricto (161 species), Senegalia (231 species) and Racosperma (960 species), the last name first proposed in 1829 by Carl Friedrich Philipp von Martius as the name of a section in Acacia, but raised to generic rank in 1835. In 2003, Pedley published a paper with 834 new combinations in Racosperma for species, most of which were formerly placed in Acacia. All but 10 of these species are native to Australasia, where it constitutes the largest plant genus.

In the early 2000s, it had become evident that the genus was not monophyletic and that several divergent lineages needed to be placed in separate genera. One lineage comprising over 900 species mainly native to Wallacea, Australia, New Guinea, and Indonesia was not closely related to the much smaller African lineage group containing the type species. This meant that the Australasian lineage, by far the most prolific in number of species, would need to be renamed. This caused controversy between South African and Australian botanists, who both claimed Acacia as a symbol of their respective nations and wished to retain the name for their respective branch.