Acacia, a genus of plants of the order legu-minosce, widely diffused over the tropical and sub-tropical regions of the earth; most abundant in Africa and Australia. They are trees or shrubs, rarely herbs, with small, usually inconspicuous petals and sepals, but with many (10-400) long stamens, which give to the heads or spikes of flowers great beauty. The pods are two-valved, jointless and woody, containing seeds of which some species are edible. The leaves are either pinnate in various degrees, or simply distended leaf stalks (phyllodia). In nearly all the species the leaves are pinnate at first, and as the plant grows gradually give place to the phyllodia, often showing all gradations between the two forms. The steins and branches are often armed with spines. The acacias are not only most ornamental trees, with slender branches, delicate foliage, and attractive flowers, but the timber is often of great value, as that of A. Ara-bica, which is much used in India for wheels; and the A. Koa has a line, hard, and variegated grain. The bark contains much tannin. A. Verek yields gum Senegal, and A. Nilotica, and Seyal gum arabic. Other valuable gums of a similar nature are obtained from other species.
The flowers of A. Farnesiana yield by distillation a delicious perfume, much prized in the East. Many species are easily cultivated under glass. Little is known of the uses of most of the 420 species that have been described.