Pajuakaasia – Acacia

Most acacias have compound pinnate leaves. In some species, however, especially in the Australian and Pacific islands species, the leaflets are reduced, and the leaf-stalks (petioles) become vertically flattened phyllodes serving the purpose of leaves. A few species lack leaves or phyllodes altogether, but possess instead modified leaf-like photosynthetic stems functioning as leaves. Many species bear spines (modified stipules), especially those species growing in arid regions. Inflorescence is a cylindric spike, globose head or panicle, solitary or in clusters, axillary or at the end of branches. The small flowers are 3-5-merous, with conspicuously long stamens, yellow or cream-colored in most species, whitish in some, even purple or red. Petals are usually more or less united, rarely absent. Calyx is campanulate, dentate, lobed or sepals are free. Stamens are numerous (more than 10), free or shortly and irregularly connate at the base. Fruit (legume) is ovate to linear, straight, arcuate or contorted, membranous to woody, rarely jointed or moniliform (resembling a string of beads). Seed is large, with a filiform funicle or fleshy aril.

Acacia s.l. used to be a pantropical genus. The new genera split from Acacia have more restricted distributions (see additional information).   

Shrubs, trees, rarely herbs, often prickly or spinose.

The genus occurs across a wide range of ecosystems, from arid deserts to montane forests. Acacias are dominant shrubs and trees in many bushland and savanna habitats. Like other legumes, Acacias fix atmospheric nitrogen.

Acacia species have several uses. The trunk yields gum (A. nilotica, A. senegal) and tannin is extracted from the bark. A few species are widely grown as ornamentals in; the most popular perhaps is A. dealbata (silver wattle). Many species are important sources of timber and firewood, and some as pulpwood. Essential oil from the flowers of A. farnesiana is used in the perfume industry. Leaves and fruits are used as animal fodder. Acacias also provide nectar for bees, and are used for soil conservation in arid regions. They are intercropped with agricultural crops because they fix nitrogen and increase soil organic matter.

In broad sense (s.l.), genus Acacia has over 1300 species. However, taxonomists have found out that the genus Acacia is polyphyletic. This discovery has led to the breaking up of Acacia into five genera, although some taxonomists (and other biologists) still continue to use the traditional Acacia sensu lato circumscription of the genus. When the genus is divided, the traditional acacias of Africa are now treated in the genera Vachellia and Senegalia, some of the American species are placed in Acaciella and Mariosousa, and the majority of species still included in the genus Acacia are confined to Australia.

Keywords:

Gum, tannin, ornamental, timber, fuel, essential oil, animal feed, bee forage, nitrogen fixing, soil conservation, Fabaceae.

In broad sense (s.l.), genus Acacia has over 1300 species. However, taxonomists have found out that the genus Acacia is polyphyletic. This discovery has led to the breaking up of Acacia into five genera, although some taxonomists (and other biologists) still continue to use the traditional Acacia sensu lato circumscription of the genus. When the genus is divided, the traditional acacias of Africa are now treated in the genera Vachellia and Senegalia, some of the American species are placed in Acaciella and Mariosousa, and the majority of species still included in the genus Acacia are confined to Australia.

Keywords:

Gum, tannin, ornamental, timber, wood, fuel, essential oil, animal feed, bee forage, nitrogen fixing, soil conservation.