(pronounced /əˈkeɪʃə/ or /əˈkeɪsiə/), known commonly as mimosa, acacia, thorntree or wattle,[2] is a polyphyletic genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae.

The genus Acacia constitutes, in its traditional circumspection, the second largest genus in Fabaceae[3] (Astragalus being the largest), with roughly 1,300 species, about 960 of them native to Australia, with the remainder spread around the tropical to warm-temperate regions of both hemispheres, including Europe, Africa, southern Asia, and the Americas (see List of Acacia species).

The genus now called Acacia represents the majority of the Australian species and a few native to southeast Asia, Réunion, and Pacific Islands.

The two final genera, Acaciella and Mariosousa, each contain about a dozen species from the Americas (but see "Classification" below for the ongoing debate concerning their taxonomy).

Queensland botanist Leslie Pedley proposed the subgenus Phyllodineae be renamed Racosperma and published the binomial names.

Acacias belong to the subfamily Mimosoideae, the major clades of which may have formed in response to drying trends and fire regimes that accompanied increased seasonality during the late Oligocene to early Miocene (~25 mya).

In common parlance, the term "acacia" is occasionally applied to species of the genus Robinia, which also belongs in the pea family.

Robinia pseudoacacia, an American species locally known as black locust, is sometimes called "false acacia" in cultivation in the United Kingdom and throughout Europe.

The vertical orientation of the phyllodes protects them from intense sunlight since with their edges towards the sky and earth they do not intercept light as fully as horizontally placed leaves.

These afford shelter for several species of Pseudomyrmex ants, which feed on extrafloral nectaries on the leaf-stalk and small lipid-rich food-bodies at the tips of the leaflets called Beltian bodies.

[19] The predominantly herbivorous spider Bagheera kiplingi, which is found in Central America and Mexico, feeds on nubs at the tips of the acacia leaves, known as Beltian bodies, which contain high concentrations of protein.

[20] In Australia, Acacia species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus including A. ligniveren.

In Myanmar, Laos, and Thailand, the feathery shoots of Acacia pennata (common name cha-om, ชะอม and su pout ywet in Burmese) are used in soups, curries, omelettes, and stir-fries.

Southern European florists use A. baileyana, A. dealbata, A. pycnantha and A. retinodes as cut flowers and the common name there for them is mimosa.

The aesthetic characteristics of acacia plants, in conjunction with their home security qualities, makes them a reasonable alternative to constructed fences and walls.

[30] Also, when God gave Moses the instructions for building the Tabernacle, he said to "make an ark" and "a table of acacia wood" (Exodus 25:10 & 23, Revised Standard Version).

[31] Acacia was used for Zulu warriors' iziQu (or isiKu) beads, which passed on through Robert Baden-Powell to the Scout movement's Wood Badge training award.

The main characters are the Wattle Babies, who are tiny people that look like acacia flowers and who interact with various forest creatures.

"[33] Gibbs was referring to the fact that an abundance of acacias flower in August in Australia, in the midst of the southern hemisphere winter.

In Yemen, the principal tannin substance was derived from the leaves of the salam-tree (Acacia etbaica), a tree known locally by the name qaraẓ (garadh).

[35][36] A bath solution of the crushed leaves of this tree, into which raw leather had been inserted for prolonged soaking, would take only 15 days for curing.

[38] For the same reasons it is favored as an erosion-control plant, with its easy spreading and resilience, some varieties of acacia are potentially invasive species.

At least fourteen Acacia species introduced to South Africa are categorized as invasive, due to their naturally aggressive propagation.

[39][citation needed] One of the most globally significant invasive acacias is black wattle A. mearnsii, which is taking over grasslands and abandoned agricultural areas worldwide, especially in moderate coastal and island regions where mild climate promotes its spread.

[40] Extensive ecological studies should be performed before further introduction of acacia varieties, as this fast-growing genus, once introduced, spreads quickly and is extremely difficult to eradicate.

It turns out that, if acacia "leaves" lack the specific glycoside-splitting enzyme, then they may be less toxic than otherwise, even those containing significant quantities of cyanic glycosides.