Acacia, commonly known aswattles[3][4] oracacias, is a genus of about1,084 species of shrubs and trees in the subfamilyMimosoideae of the pea familyFabaceae. Initially, it comprised a group of plant species native to Africa, South America, andAustralasia, but is now reserved for species mainly from Australia, with others fromNew Guinea, Southeast Asia, and the Indian Ocean.[1] The genus name isNeo-Latin, borrowed from the Greekἀκακία (akakia), a term used in antiquity to describe a preparation extracted fromVachellia nilotica, the originaltype species.
A number of species ofAcacia have been introduced to various parts of the world, and two million hectares of commercial plantations have been established.[5]
Plants in the genusAcacia are shrubs or trees withbipinnate leaves, the mature leaves sometimes reduced tophyllodes or rarely absent. There are 2 smallstipules at the base of the leaf, but sometimes fall off as the leaf matures. The flowers are borne in spikes or cylindrical heads, sometimes singly, in pairs or inracemes in the axils of leaves or phyllodes, sometimes inpanicles on the ends of branches. Each spike or cylindrical head has many small golden-yellow to pale creamy-white flowers, each with 4 or 5 sepals and petals, more than 10 stamens, and a thread-likestyle that is longer than the stamens. The fruit is a variably-shapedpod, sometimes flat or cylindrical, containing seeds with a fleshyaril on the end.[6][7][8][9][10][11]
The origin of "wattle" may be anOld Teutonic word meaning "to weave".[15] From around 700AD,watul was used inOld English to refer to the flexible woody vines, branches, and sticks which were interwoven to form walls, roofs, and fences. Since about 1810 it has been used as thecommon name for the Australianlegume trees and shrubs that can provide these branches.[15]
GenusAcacia was considered to contain some1352 species leading to 1986. That year,Leslie Pedley questioned themonophyletic nature of the genus, and proposed a split into three genera:Acaciasensu stricto (161 species),Senegalia (231 species) andRacosperma (960 species), the last name first proposed in 1829 byCarl Friedrich Philipp von Martius as the name of a section inAcacia,[16] but raised to generic rank in 1835.[17][18][19] In 2003, Pedley published a paper with 834 new combinations inRacosperma for species, most of which were formerly placed inAcacia.[20] All but 10 of these species are native toAustralasia, where it constitutes the largest plant genus.[10]
In the early 2000s, it had become evident that the genus as it stood was notmonophyletic and that several divergent lineages needed to be placed in separate genera. It turned out that one lineage comprising over 900 species mainly native to Australia, New Guinea, and Indonesia was not closely related to the much smaller group of African lineage that containedA. nilotica – thetype species. This meant that the Australasian lineage (by far the most prolific in number of species) would need to be renamed. This caused controversy between South African and Australian botanists who both claimedAcacia as a symbol of their respective nations and wished to retain the name for their respective branch.[21] Pedley's proposed name ofRacosperma for this group had received little acclaim in the botanical community, especially by Australians. Australian botanists proposed a different solution, setting a different type species forAcacia (A. penninervis) and allowing this largest number of species to remain inAcacia, resulting in the two pan-tropical lineages being renamedVachellia andSenegalia, and the two endemic American lineages renamedAcaciella andMariosousa.[22]
In 2003,Anthony Orchard andBruce Maslin filed a proposal to conserve the nameAcacia with a differenttype, in order to retain the Australasian group of species in the genusAcacia.[19] Following a controversial decision to choose a new type forAcacia in 2005, the Australian component ofAcacia s.l. now retains the nameAcacia.[23][24] At the 2011International Botanical Congress held inMelbourne, Australia, the decision to use the nameAcacia, rather than the proposedRacosperma for this genus, was upheld.[25][26] OtherAcacia s.l. taxa continue to be calledAcacia by those who choose to consider the entire group as one genus.[26]
Species ofAcacia occurs in all Australian states and territories, and on its nearby islands. About 20 species occur naturally outside Australia and7 of these also occur in Australia. One species (Acacia koa) is native toHawaii[33] and one (Acacia heterophylla) is native toMauritius andRéunion in the Indian Ocean.[9][34]
They are present in all terrestrial habitats, including alpine settings, rainforests, woodlands, grasslands, coastal dunes and deserts.[11] In drier woodlands or forests they are an important component of the understory. Elsewhere they may be dominant, as in theBrigalow Belt,Myall woodlands and theeremaeanMulga woodlands.[11]
In Australia,Acacia forest is the second most common forest type aftereucalypt forest, covering 980,000 square kilometres (378,380 sq mi) or 8% of total forest area.Acacia is also the nation's largest genus of flowering plants with almost1000 species found.[35]
The seed pods, flowers, and young leaves are generally edible either raw or cooked.[41]
Aboriginal Australians have traditionally harvested the seeds of some species, to be ground into flour and eaten as a paste or baked into a cake.Wattleseeds contain as much as 25% more protein than common cereals, and they store well for long periods due to the hard seed coats.[42] In addition to consuming the edible seed and gum, Aboriginal people also employed the timber for implements, weapons, fuel and musical instruments.[11] A number of species, most notablyAcacia mangium (hickory wattle),A. mearnsii (black wattle) andA. saligna (coojong), are economically important and are widely planted globally for wood products,tannin, firewood and fodder.[23]A. melanoxylon (blackwood) andA. aneura (mulga) supply some of the most attractive timbers in the genus. Black wattle bark supported thetanning industries of several countries, and may supply tannins for production of waterproofadhesives.[11]
InVietnam, Acacia is used inplantations of non-native species that are regularly clear-cut for paper or timber uses.[43][44]
Wattle bark collected in Australia in the 19th century was exported to Europe where it was used in thetanning process. One ton of wattle ormimosa bark contained about 68 kilograms (150 pounds) of pure tannin.[45]
The gum of some species may be used as a substitute forgum arabic, known as Australian gum or wattle gum.[46]
Some species of acacia – notablyAcacia baileyana,A. dealbata andA. pravissima – are cultivated as ornamental garden plants. The 1889 publicationUseful Native Plants of Australia describes various uses for eating.[47]
^abcKodela, Phillip G.; Maslin, Bruce R. (n.d.). Kodela, Philip G. (ed.)."Acacia". Australian Biological Resources Study. Flora of Australia. Canberra, AU: Department of Climate Change, Energy, the Environment, and Water. Retrieved9 December 2023.
^abcdeOrchard, Anthony E.; Wilson, Annette J.G. (2001).Flora of Australia. Vol. 11A, Mimosaceae, Acacia. Melbourne, VIC, AU: CSIRO. part 1,pagex.ISBN9780643067172.
^Miller, P. (1754).The Gardeners Dictionary. Vol. 1 (abridged, 4th ed.). p. 25. — only gives the name of the genus. Miller did not validly publish names of species in this book, as he did not consistently use binomial names.
^Sharr, Francis Aubi; George, Alex (2019).Western Australian Plant Names and Their Meanings (3rd ed.). Kardinya, WA: Four Gables Press. p. 56.ISBN9780958034180.
^abAustin, Daniel F. (2004).Florida Ethnobotany. Boca Raton, FL: CRC Press. p. 58.ISBN9780203491881.
^von Martius, Carl Friedrich P. (1829).Hortus regiusMonacensis. In Commission bei F . Fleischer. p. 188.
^Robin, Libby (2021). "Wattle". In Harper, Melissa; White, Richard (eds.).Symbols of Australia: imagining a nation. Sydney, NSW: NewSouth Publishing. p. 192.ISBN978-1-74223-712-1.
^The Acacia debate(PDF) (Report). IBC2011 Congress News. Retrieved5 May 2016.
^abSmith, Gideon F. & Figueiredo, Estrela (2011). "ConservingAcacia(Mill.) with a conserved type: What happened in Melbourne?".Taxon.60 (5):1504–1506.doi:10.1002/tax.605033.hdl:2263/17733.
^Brown, Gillian K.; Murphy, Daniel J.; Miller, Joseph T.; Ladiges, Pauline Y. (October 2008). "Acacia s.s. and its relationship among tropical legumes, tribe Ingeae (Leguminosae: Mimosoideae)".Systematic Botany.33 (4):739–751.doi:10.1600/036364408786500136.S2CID85910836.
^Hably, L. (1992). Herendeen, P.S.; Dilcher (eds.).Distribution of Legumes in the Tertiary of Hungary. Advances in Legume Systematics. Vol. Part 4, The fossil record. London, UK:Royal Botanic Gardens, Kew.ISBN0947643400.
^Shakryl, Alexandra K. (1992). Herendeen, P.S.; Dilcher (eds.).Leguminosae species from the territory ofAbkhazia. Advances in Legume Systematics. Vol. Part 4, The fossil record. London, UK:Royal Botanic Gardens, Kew.ISBN0947643400.
^Nambiar, E.K. Sadanandan; Harwood, Christopher E.; Kien, Nguyen Duc (2015). "Acacia plantations in Vietnam: Research and knowledge application to secure a sustainable future".Southern Forests. Sustaining the future of acacia plantation forestry.77 (1):1–10.Bibcode:2015SFJFS..77....1N.doi:10.2989/20702620.2014.999301.S2CID84167231.
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