Acacieae

The Mimosoideae are trees, herbs, lianas, and shrubs that mostly grow in tropical and subtropical climates. They comprise a clade, previously placed at the subfamily or family level in the flowering plant family Fabaceae (Leguminosae). In previous classifications (e.g. the Cronquist system), Mimosoideae refers to what was formerly considered the tribe Mimoseae. Characteristics include flowers in radial symmetry with petals that are valvate (twice divided) in bud, and have numerous showy, prominent stamens. Mimosoideae comprise about 40 genera and 2,500 species. Some classification systems, for example the Cronquist system, treat the Fabaceae in a narrow sense, raising the Mimisoideae to the rank of family as Mimosaceae. The Angiosperm Phylogeny Group treats Fabaceae in the broad sense. The Mimosoideae were historically subdivided into four tribes (Acacieae, Ingeae, Mimoseae, and Mimozygantheae). However, modern molecular phylogenetics has shown that these groupings were artificial. Several informal subgroups have been proposed, but not yet described formally as tribes. Additionally, the genus Acacia was recently segregated into five genera (Acacia sensu lato, Acaciella, Mariosousa, Senegalia, and Vachellia). The following fossil wood morphogenera have been described: Modern molecular phylogenetics suggests the following relationships: Acacieae (Dumort., 1829) is a wide-ranging, polyphyletic tribe of legumes in the Mimosoideae that is native to the tropics, subtropics, and warm-temperate regions. It includes five or six genera and some 1,450 species. In Bentham's 1842 circumscription of the subfamily Mimosoideae, Acacieae was one of its three constituent tribes, the others being Ingeae Benth. & Hook.f. and Mimoseae Bornn. His Acacieae tribe of 1842 included many genera that were subsequently assigned to tribe Ingeae Benth. In 1875, however, Bentham narrowed his definition of Acacieae so as to include only Acacia Mill. The only morphological character of Acacieae used to distinguish it from the Ingeae is the presence of free stamens (as in tribe Mimoseae). In the Ingeae they are fused in the form of a tube, whereas in the Acacieae only a few species have the stamens fused at the base. Several characters of the foliage, seeds, seed pods, pollen, and stipules are shared by the two tribes. The flower morphology of Acacia s.l. has characteristics in common with the genera Leucaena, Piptadenia, and Mimosa (tribe Mimoseae) and Enterolobium and Lysiloma (tribe Ingeae).