Acacia, commonly known as the wattles or acacias, is a large genus of shrubs, lianas and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially it comprised a group of plant species native to Africa and Australia, with the first species A. nilotica described by Linnaeus. Controversy erupted in the early 2000s when it became evident that the genus as it stood was not monophyletic, and that several divergent lineages needed to be placed in separate genera. It turned out that one lineage comprising over 900 species mainly native to Australia was not closely related to the mainly African lineage that contained A. nilotica the first and type species. This meant that the Australian lineage (by far the most prolific in number of species) would need to be renamed. Botanist Les Pedley named this group Racosperma, which was inconsistently adopted. Australian botanists proposed that this would be more disruptive than setting a different type species (A. penninervis) and allowing this large number of species to remain Acacia, resulting in the African lineage being renamed to Vachellia. This was officially adopted, but many botanists from Africa and elsewhere disagreed that this was necessary.
A number of species have been introduced to various parts of the world, and two million hectares of commercial plantations have been established. The heterogeneous group varies considerably in habit, from mat-like subshrubs to canopy trees in forest.