acacia [key], any plant of the large leguminous genus Acacia, often thorny shrubs and trees of the family Leguminosae (pulse family). Chiefly of the tropics and subtropics, they are cultivated for decorative and economic purposes. Acacias are characteristic of savanna vegetation and are especially numerous in the South African bushveld. The foliage often appears feathery because of the many small leaflets, but in some species leaflike flattened stems contain chlorophyll and take the place of leaves. Various Old World species (especially A. arabica and A. senegal ) yield gum arabic; other species, chiefly A. catechu, yield the dye catechu. Blackwood (A. melanoxylon) is valued in Australia for its hardwood timber. Other members of the genus are valuable for lac, for perfume and essential oils, and for tannins; some are used as ornamentals. The Australian acacias are commonly called wattles—their pliable branches were woven into the structure of the early wattle houses and fences—and Wattle Day celebrates the national flower at blossoming time. Many wattles are cultivated elsewhere, particularly in California, as ornamentals for their characteristic spherical, dense flowers. The Central American bullhorn acacias (e.g., A. sphaerocephala) have large hollow thorns inhabited by ants that are said to feed upon a sweet secretion of the plant and in turn guard it against leaf-eating insects. The most common acacia indigenous to the United States is the cat's-claw (A. gregii) of the arid Southwest. The biblical shittim wood is thought to have come from an acacia. Various species of locust are sometimes called acacia, and acacias may be called mimosa; all are of the same family. Acacia is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.
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