Acacia decurrens (acacia bark, early black wattle, green wattle, Sydney wattle, wattle bark, tan wattle, golden teak, or Brazilian teak) is a perennial tree or shrub native to eastern New South Wales, including Sydney, the Greater Blue Mountains Area, the Hunter Region, and south west to the Australian Capital Territory.
It is cultivated throughout Australia and the world, and has naturalised in most Australian states and in Africa, the Americas, Europe, New Zealand and the Pacific, the Indian Ocean area, and Japan. It grows to a height of 2–10 m and it flowers from July to September.
German botanist Johann Christoph Wendland first described this species as Mimosa decurrens in 1798, before his countryman Carl Ludwig Willdenow redescribed it in the genus Acacia in 1919. In his description, Willdenow did not cite Wendland but instead a 1796 description by James Donn. However as Donn's description was a nomen nudum, the proper citation is Acacia decurrens Willd. with neither older work cited.
Common names include coast green wattle, black wattle, early black wattle, Sydney green wattle, queen wattle, and in the local Dharawal language, Boo'kerrikin. It is also known as early green wattle in the Sydney basin, as it flowers in winter—earlier than similar species such as Acacia parramattensis, A. irrorata and A. mearnsii. It has attracted the vernacular name "green cancer" in South Africa, where it has become weedy.
Along with other bipinnate wattles, it is classified in the section Botrycephalae within the subgenus Phyllodineae in the genus Acacia. An analysis of genomic and chloroplast DNA along with morphological characters found that the section is polyphyletic, though the close relationships of it and many other species were unable to be resolved.
Usually 2-15 m high. They are erect and hairless. Young foliage tips are yellow. Bark is brown to dark grey colour and smooth to deeply fissured longitudinally with conspicuous intermodal flange marks.
Alternately arranged leaves with dark green on both side. Stipules are either small or none. Base of petiole swollen to form the pulvinus. Leaf blade is bipinnate. Rachis is 20-120mm long, angular and hairless. 15-45 pairs of widely spaced small leaflets (pinnules) are connected each other and 5-15 mm long by 0.4-1 mm wide, straight, parallel sided, pointed tip, tapering base, shiny and hairless or rarely sparsely hairy leaves.
The small yellow or golden-yellow flowers are very cottony in appearance and are densely attached to the stems in each head with 5-7 mm long and 60-110 mm long axillary raceme or terminal panicle. They are bisexual and fragrant. The flowers have five petals and sepals and numerous conspicuous stamens. Ovary is superior and has only one carpel with numerous ovules.
Flowering is followed by the seed pods, which are ripe over November to January.
Dark brown or reddish brown to black colour of the seed are located inside of parallel sided, flattish, smooth pod. They are 20-105 mm long by 4-8.5 mm wide with edges. Seed opens by two valves. Pods are initially hairy but they become hairless when they grow.
Dark brown or black seed is main source of reproduction. They can be spread by insects, wind or water.
Distribution and habitat
Native to Tablelands of New South Wales and Victoria. The species become naturalised in other states include Queensland, Victoria and Tasmania. Climate Temperate coastal to cool inland but not dry or hot areas of inland NSW. High rainfall areas with 600-1400mm per year, otherwise tolerant of a wide range of conditions.
Grows naturally in woodlands and dry sclerophyll forests in New South Wales, with associated trees such as Eucalyptus punctata and E. crebra. In areas where it has become naturalised, Sydney green wattle (Acacia decurrens) is generally found on roadsides, along creeklines and in waste areas. It also grows in disturbed sites nearby bushlands and open woodlands
Ordinary soil, enriched soil, mildly acidic to mildly alkaline are suitable but mainly good in dry soil for extended periods to constantly moist
The foliage serves as food for the caterpillars of the double-spotted line blue (Nacaduba biocellata), moonlight jewel (Hypochrysops delicia), imperial hairstreak (Jalmenus evagoras), ictinus blue (Jalmenus ictinus), amethyst hairstreak (Jalmenus icilius) and silky hairstreak (Pseudalmenus chlorinda) 
Uses for it include chemical products, environmental management, and wood. The flowers are edible and are used in fritters. An edible gum oozing from the tree's trunk can be used as a lesser-quality substitute for gum arabic, for example in the production of fruit jelly. The bark contains about 37-40% tannin. The flowers are used to produce yellow dye, and the seed pods are used to produce green dye. An organic chemical compound called kaempferol gives the flowers of Acacia decurrens their color. It has been grown for firewood, or as a fast-growing windbreak or shelter tree.
Acacia decurrens adapts easily to cultivation and grows very quickly. It can be used as a shelter or specimen tree in large gardens and parks. The tree can look imposing when in flower. Cultivation of A. decurrens can be started by soaking the seeds in warm water and sowing them outdoors. The seeds keep their ability to germinate for many years.
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Invasive Species Compendium.(1994). Datasheet-Acacia decurrens(green wattle).[On-line]. Availavble from: http://www.cabi.org/isc/?compid=5&dsid=2208&loadmodule=datasheet&page=481&site=144
HerbiGuide. (1988). Available from: http://www.herbiguide.com.au/Descriptions/hg_Early_Black_Wattle.htm
Queensland Government, Weeds of Australia Biosecurity Queensland Edition. (2011) Availavble from: http://keyserver.lucidcentral.org/weeds/data/03030800-0b07-490a-8d04-0605030c0f01/media/Html/Acacia_decurrens.htm
A view from Yallaroo. (2009) Availavble from: http://www.yallaroo.com.au/A.decurrens.htm
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