The generic name derives from ἀκακία (akakia), the name given by early Greek botanist-physician Pedanius Dioscorides (middle to late first century) to the medicinal tree A. nilotica in his book Materia Medica.[2] This name derives from the Greek word for its characteristic thorns, ἀκίς (akis; "thorn").[3] The species name nilotica was given by Linnaeus from this tree's best-known range along the Nile river.
The genus Acacia previously contained roughly 1300 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. However, in 2005 the genus was divided into five separate genera under the tribe "Acacieae." The genus Acacia was retained for the majority of the Australian species and a few in tropical Asia, Madagascar and Pacific Islands. Most of the species outside Australia, and a small number of Australian species, were reclassified into Vachellia and Senegalia. The two final genera, Acaciella and Mariosousa, each contain about a dozen species from the Americas.
http://en.wikipedia.org/wiki/Acacia
Botany
Acacia is a large umbraculiform tree growing to a height of 20 to 25 meters. Bark is rough and furrowed. Branches are widespread. Leaves are evenly bipinnate and hairy underneath. Pinnae are 8 to 12 and 15 centimeters long or less. Leaflets are 12 to 16 in the upper