Acacia
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| Missing image Blackwood-Linton.jpg Acacia tree in Thailand A Blackwood in flower. | ||||||||||||||
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~1,300; See List of Acacia species |
Acacia is a genus of shrubs and trees of Gondwanian origin belonging to the subfamily Mimosoideae of the Pea Family Fabaceae, first described from Africa by Linnaeus in 1773.
There are roughly 1300 species worldwide: about 950 of them being native to Australia, while the remainder are spread around the dry tropical to warm-temperate regions of both hemispheres, including Africa, southern Asia, and the Americas. The northernmost species is Acacia greggii (Catclaw Acacia), reaching 37°10' N in southern Utah in the United States; the southernmost are Acacia dealbata (Silver Wattle), Acacia longifolia (Coast Wattle or Sydney Golden Wattle), 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, 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 (as in Acacia purpureapetala) or red (in the recently grown cultivar Acacia leprosa 'Scarlet Blaze').
The plants often bear spines, especially those 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, Acacia giraffae, the Camelthorn of Africa. In the Central American Acacia sphaerocephala (Bullthorn Acacia) and Acacia spadicigera, the large thorn-like stipules are hollow and afford shelter for ants, which feed on a secretion of honey on the leaf-stalk and curious food-bodies at the tips of the leaflets; in return they protect the plant against leaf-eating insects.
In common parlance the term "acacia" is occasionally misapplied to species of the genus Robinia, which also belongs in the pea family, although placed in a different subgenus. Robinia pseudoacacia, an American species normally known as Black locust, is sometimes called "false acacia" in cultivation in Britain.
Uses
Acaciaauriculiformis1web.jpg
Various species yield gum.
True gum arabic is the product of Acacia senegal, abundant in dry tropical west Africa from Senegal to northern Nigeria.
Acacia arabica is the gum-arabic tree of India, but yields a gum inferior to the true gum-arabic.
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.
The seeds of Acacia niopo are roasted and used as snuff in South America.
The bark of Acacia arabica, under the name of babul or babool, is used in Scinde for tanning. In Ayurvedic medicine, babul is considered a remedy that is helpful for treating premature ejaculation.
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). Black Wattle plantations in South Africa The pods of Acacia nilotica (under the name of neb-neb), and of other African species are also rich in tannin and used by tanners.
Some species afford 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 homalophylla (Myall Wood, also Australian), which yields a fragrant timber, used for ornamental purposes. Acacia formosa supplies the valuable Cuban timber called sabicu. Acacia seyal is thought to be the shittah tree of the Bible, which supplied shittim-wood. This was used in the construction of the Ark of the Covenant. As a spiritual icon it is also one of the most powerful symbols in freemasonry, representing the eternal soul and purity of the soul. Acacia heterophylla from Mauritius and Bourbon, and Acacia koa from the Hawaiian Islands are excellent timber trees.
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.
Acacia farnesiana is used in the perfume industry due to its strong fragrance.
In Australia, Acacia species are sometimes used as food plants by the larvae of hepialid moths of the genus Aenetus. These burrow horizontally into the trunk then vertically down.
Species
There are over 1,300 species of Acacia. See List of Acacia species for a complete listing.
External links
- World Wide Wattle (http://www.worldwidewattle.com/)
- Wayne's Word (http://waynesword.palomar.edu/plaug99.htm) on "The Unforgettable Acacias"
- Section Eclectic herbal information
- Acacia catechu (Catechu) (http://www.ibiblio.org/herbmed/eclectic/kings/acacia-cate.html) King's American Dispensatory @ Henriette's Herbal
- Acacia senegal (Gum Arabic) (http://www.ibiblio.org/herbmed/eclectic/kings/acacia.html) King's American Dispensatory @ Henriette's Herbal
- Acacia Bark (http://www.botanical.com/botanical/mgmh/a/acaci003.html) Mrs. Grieve's "A Modern Herbal" @ Botanical.com
- Acacia Gum (http://www.botanical.com/botanical/mgmh/a/acaci006.html) Mrs. Grieve's "A Modern Herbal" @ Botanical.com
- Catechu, Black (http://www.botanical.com/botanical/mgmh/c/catbla35.html) Mrs. Grieve's "A Modern Herbal" @ Botanical.com
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