Acacia, commonly known as the wattles or acacias, is a large genus of shrubs and trees in the subfamily Mimosoideae of the pea family Fabaceae. Initially, it comprised a group of plant species native to Africa and Australasia, but it has now been limited to contain only the Australasian species. The genus name is New Latin, borrowed from the Greek ἀκακία (akakia), a term used by Dioscorides for a preparation extracted from the leaves and fruit pods of Vachellia nilotica, the original type of the genus. In his Pinax (1623), Gaspard Bauhin mentioned the Greek ἀκακία from Dioscorides as the origin of the Latin name.
In the early 2000s it had become evident that the genus as it stood was not monophyletic 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 contained A. nilotica—the type species. This meant that the Australasian lineage (by far the most prolific in number of species) would need to be renamed. Botanist Leslie Pedley named this group Racosperma, which received little acclaim in the botanical community. Australian botanists proposed a less disruptive solution setting a different type species for Acacia (A. penninervis) and allowing this largest number of species to remain in Acacia, resulting in the two Pan-Tropical lineages being renamed Vachellia and Senegalia, and the two endemic American lineages renamed Acaciella and Mariosousa. Although many botanists still disagreed that this was necessary, this solution was eventually officially adopted at the Melbourne International Botanical Congress in 2011.
Acacia remains a widely used common name across genera.
A number of species have been introduced to various parts of the world, and two million hectares of commercial plantations have been established. The heterogeneous group varies considerably in habit, from mat-like subshrubs to canopy trees in a forest.
The genus was first validly named in 1754 by Philip Miller. In 1913 Nathaniel Lord Britton and Addison Brown selected Mimosa scorpioides L. (≡ Acacia scorpioides (L.) W.Wight = Acacia nilotica (L.) Delille), a species from Africa, as the lectotype of the name. The genus as recognized in 1986 contained 1352 species. That year however, Pedley published a paper in which he questioned the monophyletic nature of the genus, and proposed a split into three genera: Acacia sensu stricto (161 species), Senegalia (231 species) and Racosperma (960 species), the last name first proposed in 1829 by Carl Friedrich Philipp von Martius as the name of a section in Acacia, but raised to generic rank in 1835. In 2003, Pedley published a paper with 834 new combinations in Racosperma for species, most of which were formerly placed in Acacia. All but 10 of these species are native to Australasia, where it constitutes the largest plant genus.
In 2003, Anthony Orchard and Bruce Maslin filed a proposal to conserve the name Acacia with a different type in order to retain the Australasian group of species in the genus Acacia. Following a controversial decision to choose a new type for Acacia in 2005, the Australian component of Acacia s.l. now retains the name Acacia. At the 2011 International Botanical Congress held in Melbourne, the decision to use the name Acacia, rather than the proposed Racosperma for this genus, was upheld. Other Acacia s.l. taxa continue to be called Acacia by those who choose to consider the entire group as one genus.
Australian species of the genus Paraserianthes s.l. are deemed its closest relatives, particularly P. lophantha. The nearest relatives of Acacia and Paraserianthes s.l. in turn include the Australian and South East Asian genera Archidendron, Archidendropsis, Pararchidendron and Wallaceodendron, all of the tribe Ingeae.
The origin of "wattle" may be an Old Teutonic word meaning "to weave". From around 700 CE, watul was used in Old English to refer to the interwoven branches and sticks which formed fences, walls and roofs. Since about 1810 it refers to the Australian legumes that provide these branches.
One species of Acacia (sensu stricto) is native to Madagascar, one to Reunion island, 12 to Asia, and the remaining species (over 900) are native to Australasia and the Pacific Islands. These species were all given combinations by Pedley when he erected the genus Racosperma, hence Acacia pulchella, for example, became Racosperma pulchellum. However, these were not upheld with the retypification of Acacia.
Acacias in Australia probably evolved their fire resistance about 20 million years ago when fossilised charcoal deposits show a large increase, indicating that fire was a factor even then. With no major mountain ranges or rivers to prevent their spread, the wattles began to spread all over the continent as it dried and fires became more common. They began to form dry, open forests with species of the genera Allocasuarina, Eucalyptus and Callitris (cypress-pines).
The southernmost species in the genus 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.
An Acacia-like 14 cm long fossil seed pod has been described from the Eocene of the Paris Basin. Acacia like fossil pods under the name Leguminocarpon are known from late Oligocene deposits at different sites in Hungary. Seed pod fossils of †Acacia parschlugiana and †Acacia cyclosperma are known from Tertiary deposits in Switzerland,. †Acacia colchica has been described from the Miocene of West Georgia. Pliocene fossil pollen of an Acacia sp. has been described from West Georgia (including Abkhazia). Oldest records of fossil Acacia pollen in Australia are from the late Oligocene epoch, 25 million years ago.
Distribution and habitat
They are present in all terrestrial habitats, including alpine settings, rainforests, woodlands, grasslands, coastal dunes and deserts. In drier woodlands or forests they are an important component of the understory. Elsewhere they may be dominant, as in the Brigalow Belt, Myall woodlands and the eremaean Mulga woodlands.
In Australia, Acacia forest is the second most common forest type after eucalypt 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 almost 1,000 species found.
Several of its species bear vertically oriented phyllodes, which are green, broadened leaf petioles that function like leaf blades, an adaptation to hot climates and droughts. Some phyllodinous species have a colourful aril on the seed. A few species have cladodes rather than leaves.
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. The seeds contain as much as 25% more protein than common cereals, and they store well for long periods due to the hard seed coats. In addition to utilizing the edible seed and gum, the people employed the timber for implements, weapons, fuel and musical instruments. A number of species, most notably A. mangium (hickory wattle), A. mearnsii (black wattle) and A. saligna (coojong), are economically important and are widely planted globally for wood products, tannin, firewood and fodder. A. melanoxylon (blackwood) and A. aneura (mulga) supply some of the most attractive timbers in the genus. Black wattle bark supported the tanning industries of several countries, and may supply tannins for production of waterproof adhesives.
Acacia is a common food source and host plant for butterflies of the genus Jalmenus. The imperial hairstreak, Jalmenus evagoras, feeds on at least 25 acacia species. Many reptiles feed on the sap as well, such as the native house gecko in Australia.
Wattle bark collected in Australia in the 19th century was exported to Europe where it was used in the tanning process. One ton of wattle or mimosa bark contained about 68 kilograms (150 pounds) of pure tannin.
In ancient Egypt, an ointment made from the ground leaves of an Acacia (sensu lato) was used to treat hemorrhoids. Acacia (sensu lato) is repeatedly mentioned in the Book of Exodus, perhaps referring to Vachellia tortilis (previously known as Acacia raddiana), in regards to the construction of the Tabernacle.
The hardened sap of various species of the acacia tree (sensu lato) are known as acacia gum. Acacia gum is used as an emulsifier in food, a binder for watercolour painting, an additive to ceramic glazes, a binding in gum bichromate photography, a protective layer in the lithographic processes and as a binder to bind together fireworks.
Acacia honey is not collected from plants in the acacia family, but rather from Robinia pseudoacacia, known as black locust in North America. Honey collected from Caragana arborescens is sometimes also called (yellow) acacia honey. See also Monofloral honey.
Some species of acacia – notably A. baileyana, A. dealbata and A. pravissima – are cultivated as ornamental garden plants. The 1889 publication 'Useful native plants of Australia' describes various uses for eating.
- Pedley, L. (2002). "A conspectus of Acacia subgen. Acacia in Australia". Austrobaileya 6(2): 177–186.
- Pedley, L. (2003). A synopsis of Racosperma C.Mart". Austrobaileya 6(3): 445–496.
- Kew Science. "Acacia Mill. in Plants Of the World Online".
- Pedley, L. (2003). "A synopsis of Racosperma C.Mart. (Leguminosae: Mimosoideae)". Austrobaileya. 6 (3): 445–496. JSTOR 41738994.
- Wu, Delin; Nielsen, Ivan C. (2009). "Flora of China, 6. Tribe Acacieae" (PDF). Missouri Botanical Garden Press. Retrieved 19 November 2015.
- Vachellia nilotica in Plants of the World online (POWO)
- Bauhin, G. (1623). Pinax theatri botanici: 391
- Kyalangalilwa, B.; Boatwright, J.S.; Daru, B.H.; Maurin, O.; Van der Bank, M. (2013). "Phylogenetic position and revised classification of Acacia s.l. (Fabaceae: Mimosoideae) in Africa, including new combinations in Vachellia and Senegalia". Botanical Journal of the Linnean Society. 172 (4): 500–523. doi:10.1111/boj.12047.
- Midgley, S.J.; Turnbull, J.W. (2003). "Domestication and use of Australian acacias: case studies of five important species". Australian Systematic Botany. 16 (1): 89–102. doi:10.1071/SB01038.
- Murphy, Daniel J. (2008). "A review of the classification of Acacia (Leguminosae, Mimosoideae)". Muelleria. 26 (1): 10–26. Retrieved 22 November 2015.
- Orchard, Anthony E.; Wilson, Annette J.G. (2001). Flora of Australia. Volume 11A, Mimosaceae, Acacia part 1. Melbourne: CSIRO. pp. x–. ISBN 9780643067172.
- Miller, P. (1754). The Gardeners Dictionary, abbridged. 1 (4 ed.). p. . Only the name of the genus, Miller did not validly publish names of species in this work as he did not consistently use binomial names.
- Britton, N.L.; Brown, A. (1913). An illustrated flora of the northern United States. 2 (2 ed.). p. 330.
- Martius, C.F.P. von (1829). Hortus regius Monacensis. p. 188.
- Martius, C.F.P. von (1835). Hortus regius Monacensis seminifer. 1835. p. 4.
- Pedley, L. (1986). "Derivation and dispersal of Acacia (Leguminosae), with particular reference to Australia, and the recognition of Senegalia and Racosperma". Botanical Journal of the Linnean Society. 92 (3): 219–254. doi:10.1111/j.1095-8339.1986.tb01429.x. PMC 7188348. PMID 32362685.
- Orchard, A.E.; Maslin, B.R. (2003). "Proposal to conserve the name Acacia (Leguminosae: Mimosoideae) with a conserved type". Taxon. 52: 362–363. doi:10.2307/3647418. JSTOR 3647418.
- Thiele, Kevin R. (February 2011). "The controversy over the retypification of Acacia Mill. with an Australian type: A pragmatic view" (PDF). Taxon. 60 (1): 194–198. doi:10.1002/tax.601017. Retrieved 15 November 2015.
- Brummitt, R. K. (December 2010). "(292) Acacia: a solution that should be acceptable to everybody" (PDF). Taxon. 59 (6): 1925–1926. doi:10.1002/tax.596050. Retrieved 19 November 2015.
- "The Acacia debate" (PDF). IBC2011 Congress News. Retrieved May 5, 2016.
- Smith, Gideon F. & Figueiredo, Estrela (2011). "Conserving Acacia 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.; Daniel J. Murphy & Pauline Y. Ladiges (2011). "Relationships of the Australo-Malesian genus Paraserianthes (Mimosoideae: Leguminosae) identifies the sister group of Acacia sensu stricto and two biogeographical tracks". Cladistics. 27 (4): 380–390. doi:10.1111/j.1096-0031.2011.00349.x. S2CID 85416700.
- Brown, Gillian K.; Murphy, Daniel J.; Miller, Joseph T.; Ladiges, Pauline Y. (1 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. S2CID 85910836.
- Austin, Daniel F. (2004). Florida ethnobotany Fairchild Tropical Garden, Coral Gables, Florida, Arizona-Sonora Desert Museum, Tucson, Arizona: with more than 500 species illustrated by Penelope N. Honychurch ... [et al.] Boca Raton, Florida: CRC Press. p. 58. ISBN 9780203491881.
- Fossil Plants by Paul Kenrick & Paul Davis, Natural History Muyseum, London, 2004, ISBN 0-565-09176-X
- Distribution of Legumes in the Tertiary of Hungary by L. Hably, Advances in Legume Systematics: Part 4, The Fossil Record, Ed. P.S. Herendeen & Dilcher, 1992, The Royal Botanic Gardens, Kew, ISBN 0947643400
- Leguminosae species from the territory of Abkhazia by Alexandra K. Shakryl, Advances in Legume Systematics: Part 4, The Fossil Record, Ed. P.S. Herendeen & Dilcher, 1992, The Royal Botanic Gardens, Kew, ISBN 0947643400
- The Greening of Gondwana by Mary E. White, Reed Books Pty Ltd, Australia, Reprinted issue 1988, ISBN 0730101541
- "Acacia forest". Commonwealth of Australia. 6 February 2017. Retrieved 19 April 2017.
- Armstrong, W. P. "Unforgettable Acacias, A Large Genus Of Trees & Shrubs". Wayne's Word. Archived from the original on 10 November 2015. Retrieved 17 November 2015.
- Tan, Ria. "Acacia auriculiformis, Black Wattle". Naturia. Archived from the original on 5 May 2015. Retrieved 17 November 2015.
- "Acacia, Thorntree". EOL. Retrieved 22 November 2015.
- Biology of Australian butterflies. Kitching, R. L. (Roger Laurence), 1945-, CSIRO (Australia). Collingwood, VIC, Australia: CSIRO Pub. 1999. ISBN 978-0643050273. OCLC 40792921.CS1 maint: others (link)
- The National Cyclopaedia of Useful Knowledge Vol II, (1847) Charles Knight, London, p.873.
- Ellesmore, Windsor (2002). "Surgical History of Haemorrhoids". In Charles MV (ed.). Surgical Treatment of Haemorrhoids. London: Springer.
- "Plants of the Bible - ODU Plant Site". Old Dominion University. 11 April 2007. Retrieved 3 October 2016.
- Erik Hornung 'The Pharaoh' in Sergio Donadoni, The Egyptians, The University of Chicago Press, 1997. p. 291
- J. H. Maiden (1889). Useful native plants of Australia : Including Tasmania. Turner and Henderson, Sydney.
- Leong, L. E.; Khan, S.; Davis, C. K.; Denman, S. E.; McSweeney, C. S. (2017). "Fluoroacetate in plants - a review of its distribution, toxicity to livestock and microbial detoxification". Journal of Animal Science and Biotechnology. 8: 55. doi:10.1186/s40104-017-0180-6. PMC 5485738. PMID 28674607.