| Black wattle | |
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Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Rosids |
| Order: | Fabales |
| Family: | Fabaceae |
| Subfamily: | Caesalpinioideae |
| Clade: | Mimosoid clade |
| Genus: | Acacia |
| Species: | A. decurrens |
| Binomial name | |
| Acacia decurrens | |
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| Occurrence data fromAVH | |
| Synonyms | |
Acacia decurrens, commonly known asblack wattle orearly green wattle, is a perennial tree or shrub native to easternNew South Wales, includingSydney, theGreater Blue Mountains Area, theHunter Region, and southwest to theAustralian Capital Territory. It grows to a height of 2–15 m (7–50 ft) and it flowers from July to September.
Cultivated throughout Australia and in many other countries,Acacia decurrens has naturalised in most Australian states and inAfrica, theAmericas,Europe,New Zealand and thePacific, theIndian Ocean area, andJapan.
Acacia decurrens is a fast-growing tree, reaching anywhere from 2 to 15 m (7–50 ft) high. The bark is brown to dark grey colour and smooth to deeply fissured longitudinally with conspicuous intermodal flange marks. The branchlets have longitudinal ridges running along them that are unique to the species.[1] Young foliage tips are yellow. .
Alternately arranged leaves are dark green on both sides.Stipules are either small or absent. The base of thepetiole is swollen to form thepulvinus. The leaf blade isbipinnate and therachis is 20–120 mm long, angular and hairless. 15–45 pairs of widely spaced small leaflets (pinnules) are connected with each other and 5–15 mm long by 0.4–1 mm wide. They are straight, parallel-sided, with a pointed tip, tapering base, shiny and hairless or rarely sparsely hairy.
The small yellow or golden-yellow flowers are very cottony in appearance and are densely attached to the stems, with each head 5–7 mm long, forming a 60–110 mm long axillary raceme or terminal panicle. They are bisexual and fragrant. The flowers have five petals and sepals with numerous conspicuous stamens. The ovary is superior and has only one carpel with numerous ovules.
Flowering is followed by the formation of seed pods, which ripen from November to January.[2]
Dark brown or reddish brown to black in colour, the seed are located inside a parallel-sided, flattish, smooth pod. They are 20–105 mm long by 4–8.5 mm wide with edges. The seed opens by two valves. Pods are initially hairy but they become hairless as they grow.
German botanistJohann Christoph Wendland first described this species asMimosa decurrens in 1798,[3] before his countrymanCarl Ludwig Willdenow redescribed it in the genusAcacia in 1919.[4] In his description, Willdenow did not cite Wendland but instead a 1796 description byJames Donn. However, as Donn's description was anomen nudum, the proper citation isAcacia decurrens Willd. with neither older work cited.[1]
George Bentham classifiedA. decurrens in the seriesBotrycephalae in his 1864Flora Australiensis.[5]
Queensland botanistLes Pedley reclassified the species asRacosperma decurrens in 2003, when he proposed placing almost all Australian members of the genus into the new genusRacosperma.[6] However, this name is treated as asynonym of its original name.[4]
Common names include coast green wattle, black wattle, early black wattle, Sydney green wattle, queen wattle,[4] and in the localDharawal language,Boo'kerrikin.[7][8]Maiden noted that it was calledWat-tah by the indigenous people of Cumberland (Parramatta) and Camden districts.[9] Sydney wattle was a name coined byvon Mueller and early settlers around Penrith called it green wattle. Feathery wattle was another early name.[9] It is also known as early green wattle in the Sydney basin, as it flowers in winter—earlier than similar species, such as Parramatta wattle (Acacia parramattensis), blueskin (A. irrorata) and late black wattle (A. mearnsii).[10] It has attracted the vernacular name 'green cancer' in South Africa, where it has become weedy.[11]
Other names include acacia bark, wattle bark, tan wattle, golden teak, and Brazilian teak.[citation needed]
Along with other bipinnate wattles, it is classified in thesectionBotrycephalae within thesubgenusPhyllodineae in thegenusAcacia. An analysis ofgenomic andchloroplast DNA along with morphological characters found that the section ispolyphyletic, though the close relationships ofA. decurrens and many other species were unable to be resolved.[12]
Acacia decurrens is native to tablelands of New South Wales and Victoria. It is found in temperate coastal to cool inland areas, but not dry or hot areas of inland NSW. It prefers high rainfall areas with 600–1,400 mm (24–55 in) per year, and is otherwise tolerant of a wide range of conditions. In woodlands and drysclerophyll forests in New South Wales, it grows with trees such as grey gum (Eucalyptus punctata) and narrow-leaved ironbark (E. crebra).[2] In areas where it has become naturalised,Acacia decurrens is generally found on roadsides, along creeklines and in waste areas. It also grows in disturbed sites nearby bushlands and open woodlands.[2]
It was extensively planted in New South Wales, and it is difficult to tell whether it is native or naturalised in areas near its native range.[13] The species became naturalised in other states including Queensland, Victoria and Tasmania. It grows on shale and sandstone soils with medium nutrients and good drainage.[2]
Despite its invasive nature, it has not been declared a noxious weed by any state or Australian government body.[13]
The dark brown or black seed is the main source of reproduction. They can be spread by ants or birds, and form a seedbank in the soil. Seedlings generally grow rapidly after bushfire, and the species can colonise disturbed areas.[2] Trees can live for 15 to 50 years.[2]
Sulphur-crested cockatoos eat the unripe seed.[2]
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).[14]
The wood serves as food for larvae of the jewel beetle speciesAgrilus australasiae,Cisseis cupripennis andC. scabrosula.[15]
Uses ofAcacia decurrens include chemical products, environmental management, and wood. The flowers are edible and are used infritters. An edible gum oozing from the tree's trunk can be used as a lesser-quality substitute forgum arabic, for example in the production of fruit jelly. The bark contains about 37–40%tannin. The flowers are used to produce yellowdye, and the seed pods are used to produce green dye.[16] An organic chemical compound calledkaempferol gives the flowers ofA. decurrens their color.[17] It has been grown for firewood, or as a fast-growing windbreak or shelter tree.[18]
In theDharawal story of the Boo'kerrikin Sisters, one of the kindly sisters was turned intoAcacia decurrens. The other two sisters were turned intoA. parvipinnula andA. parramattensis.[8] The flowering ofA. decurrens was used as aseasonal indicator of the ceasing of cold winds and the beginning of a period of gentle rain.[19]
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.[18] The tree can look imposing when in flower.[11] Cultivation ofA. 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.[20]
Fieldwork conducted in the Southern Highlands found that the presence of bipinnate wattles (either as understory or tree) was related to reduced numbers ofnoisy miners, an aggressive species of bird that drives off small birds from gardens and bushland, and hence recommended the use of these plants in establishinggreen corridors and revegetation projects.[21]
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