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Acacia is a genus of shrubs and trees belonging to the subfamily Mimosoideae of the family Fabaceae, first described in Africa by the Swedish botanist Carolus Linnaeus in 1773.
Acacias are also known as thorntrees or wattles, including the yellow-fever acacia and umbrella acacias.
There are roughly 1300 species of Acacia worldwide, about 960 of them native to Australia, with the remainder spread around the tropical to warm-temperate regions of both hemispheres, including Africa, southern Asia, and the Americas.
The genus Acacia is apparently not monophyletic. This discovery has led to the breaking up of Acacia into five new genera as discussed in list of Acacia species. In common parlance the term "acacia" is occasionally misapplied 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.
The southernmost species in the genus are Acacia dealbata (Silver Wattle), Acacia longifolia (Coast Wattle or Sydney Golden pattle), Acacia mearnsii (Black Wattle), and Acacia melanoxylon (Blackwood), reaching 43°30' S in Tasmania, Australia, while Acacia caven (Espinillo Negro) reaches nearly as far south in northeastern Chubut Province of Argentina. Australian species are usually called wattles, while African and American species tend to be known as acacias.
The leaves of acacias are compound pinnate in general. In some species, however, more especially in the Australian and Pacific islands species, the leaflets are suppressed, and the leaf-stalks (petioles) become vertically flattened, and serve the purpose of leaves. These are known as phyllodes. The vertical orientation of the phyllodes protects them from intense sunlight, as with their edges towards the sky and earth they do not intercept light so fully as horizontally placed leaves. A few species (such as Acacia glaucoptera) lack leaves or phyllodes altogether, but possess instead cladodes, modified leaf-like photosynthetic stems functioning as leaves.
The small flowers have five very small petals, almost hidden by the long stamens, and are arranged in dense globular or cylindrical clusters; they are yellow or cream-colored in most species, whitish in some, even purple (Acacia purpureapetala) or red (Acacia leprosa Scarlet Blaze).
The plants often bear spines, especially those species growing in arid regions. These sometimes represent branches which have become short, hard and pungent, or sometimes leaf-stipules. Acacia armata is the Kangaroo-thorn of Australia and Acacia erioloba is the Camelthorn of Africa.
In the Central American Acacia sphaerocephala, Acacia cornigera, and Acacia collinsii (collectively known as the bullthorn acacias), the large thorn-like stipules are hollow and afford shelter for ants, which feed on a secretion of sap on the leaf-stalk and small, lipid-rich food-bodies at the tips of the leaflets called Beltian bodies; in return they usually protect the plant against herbivores. Some species of ants will also fight off competing plants around the acacia, cutting off the offending plant's leaves with their jaws and ultimately killing it, while other ant species will do nothing to benefit their host.
In Australia, Acacia species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus including A. ligniveren. These burrow horizontally into the trunk then vertically down. Other Lepidoptera larvae which have been recorded feeding on Acacia include Brown-tail, Endoclita malabaricus and Turnip Moth. The leaf-mining larvae of some bucculatricid moths also feed on Acacia: Bucculatrix agilis feeds exclusively on Acacia horrida and Bucculatrix flexuosa feeds exclusively on Acacia nilotica.
Acacia seeds are often used for food and a variety of other products.
In Burma, 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.
Honey made by bees using the acacia flower as forage is considered a delicacy, appreciated for its mild flowery taste, soft running texture and glass like appearance.
It is listed as an ingredient in soft drinks Fresca and Barq's Root Beer. Läkerol , the refreshment pastille originated in Sweden list as an ingredient. As do Altoids peppermints.
Acacia arabica is the gum-Arabic tree of India, but yields a gum inferior to the true gum-Arabic.
Many Acacia species have important uses in traditional medicine. Most all of the uses have been shown to have a scientific basis, since chemical compounds found in the various species have medicinal effects. In Ayurvedic medicine, Acacia nilotica is considered a remedy that is helpful for treating premature ejaculation. A 19th century Ethiopian medical text describes a potion made from an Ethiopian species of Acacia (known as grar) mixed with the root of the tacha, then boiled, as a cure for rabies. An astringent medicine, called catechu or cutch, is procured from several species, but more especially from Acacia catechu, by boiling down the wood and evaporating the solution so as to get an extract.
A few species are widely grown as ornamentals in gardens; the most popular perhaps is Acacia dealbata (Silver Wattle), with its attractive glaucous to silvery leaves and bright yellow flowers; it is erroneously known as "mimosa" in some areas where it is cultivated, through confusion with the related genus Mimosa.
Another ornamental acacia is Acacia xanthophloea (Fever Tree). Southern European florists use Acacia baileyana, Acacia dealbata, Acacia pycnantha and Acacia retinodes as cut flowers and the common name there for them is mimosa.
Ornamental species of acacia are also used by homeowners and landscape architects for home security purposes. The sharp thorns of some species deter unauthorized persons from entering private properties, and may prevent break-ins if planted under windows and near drainpipes. The aesthetic characteristics of acacia plants, in conjunction with their home security qualities, makes them a considerable alternative to artificial fences and walls.
The ancient Egyptians used Acacia in paints.
Acacia farnesiana is used in the perfume industry due to its strong fragrance. The use of Acacia as a fragrance dates back centuries. In The Bible, burning of acacia wood as a form of incense is mentioned several times.
Symbolism and ritual
The Acacia is used as a symbol in Freemasonry, to represent purity and endurance of the soul, and as funerary symbolism signifying resurrection and immortality.
Several parts (mainly bark, root and resin) of Acacia are used to make incense for rituals. Acacia is used in incense mainly in India, Nepal, Tibet and China. Smoke from Acacia bark is thought to keep demons and ghosts away and to put the gods in a good mood. Roots and resin from Acacia are combined with rhododendron, acorus, cytisus, salvia and some other components of incense. Both people and elephants like an alcoholic beverage made from acacia fruit. According to Easton's Bible Dictionary, the Acacia tree may be the “burning bush” (Exodus 3:2) which Moses encountered in the desert
In the Quran 56:29, the acacia are mentioned as the flowers that companions in heaven will be wearing.
The bark of various Australian species, known as wattles, is very rich in tannin and forms an important article of export; important species include Acacia pycnantha (Golden Wattle), Acacia decurrens (Tan Wattle), Acacia dealbata (Silver Wattle) and Acacia mearnsii (Black Wattle).
Most acacia species are used for valuable timber; such are Acacia melanoxylon (Blackwood) from Australia, which attains a great size; its wood is used for furniture, and takes a high polish; and Acacia omalophylla (Myall Wood, also Australian), which yields a fragrant timber, used for ornamental purposes. Acacia seyal is thought to be the Shittah-tree of the Bible, which supplied shittim-wood. According to the Book of Exodus, this was used in the construction of the Ark of the Covenant. Acacia koa from the Hawaiian Islands and Acacia heterophylla from Réunion island are both excellent timber trees.
Phytochemistry of Acacias
As mentioned previously, Acacias contain a number of organic compounds that defend them from pests and grazing animals. Many of these compounds are psychoactive in humans. The alkaloids found in Acacias include Dimethyltryptamine (DMT) and N-methyltryptamine (NMT). The plant leaves, stems and/or roots are sometimes made into a brew together with some MAOI-containing plant and consumed orally for healing, ceremonial or religious uses. Egyptian mythology has associated the acacia tree with characteristics of the tree of life (cf. article on the Legend of Osiris and Isis).
List of Acacia Species Having Little or No Alkaloids in the Material Sampled:
0% C 0.02%, C...Concentration of Alkaloids [%]
Nineteen different species of Acacia in the Americas contain cyanogenic glycosides, which, if exposed to an enzyme which specifically splits glycosides, can release hydrogen cyanide (HCN) in the acacia "leaves." This sometimes results in the poisoning death of livestock.
If fresh plant material spontaneously produces 200 ppm or more HCN, then it is potentially toxic. This corresponds to about 7.5 μmol HCN per gram of fresh plant material. 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 quatities of cyanic glycosides.
Some Acacia species containing cyanogens:
There are over 1,300 species of Acacia. See List of Acacia species for a more complete listing.
Perhaps the most famous acacia is the Arbre du Ténéré in Niger. The reason for the tree's fame is that it used to be the most isolated tree on in the world, approximately, 400 km far from any other tree. The tree was knocked down by a truck driver in 1973.
|This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Acacia". A list of authors is available in Wikipedia.|