Early Black Wattle
Acacia decurrens (Wendl.) Willd.
Synonyms – Acacia deanei, Mimosa decurrens
Family: Fabaceae (was Mimosaceae)Names:
Acacia was the name of a thorny Egyptian tree.
Decurrens refers to the continuous ridge on the petiole and branchlet.
Wattle comes from British settlers making wattle and daub buildings using Callicoma serratifolia branches which was then called Black Wattle and is similar to the other Acacias of the area.
Black Wattle refers to the black bark and it is a member of the Wattle or Acacia genus.
Other Names:Black Wattle
Summary:Early Black Wattle is an erect, shrub or small tree to 10 m high with black or brown often fissured bark and dark green foliage. The main leaf-axis is 20-145 mm long and has 3-13 pairs of branches. Each of these side branches has 15-45 pairs of narrow leaflets. The leaflets are 5-15 mm long and 0.4-1 mm wide and hairless. The golden globular flower heads are 5-7 mm across and arranged in 10 to 45-headed sprays. The seed pods are flat, 2-10.5 cm long and 4-8.5 mm wide. The bark is smooth or fissured, brown, greyish black or black, with conspicuous internodal flange marks. Native to New South Wales, it is a garden escape and now a weed of roadsides and waste land sometimes invading disturbed woodland particularly along creeks. The main flowering is usually from July to October.
Description:See the Weedy_Acacia_Key
Leaves:Alternate. Young leaves are light green and become dark green with age. Bipinnate.
Stipules – Small or none.
Petiole – (0.7)15-25 mm long, ridged. 1-2 prominent glands. Base of petiole swollen to form the pulvinus. Initially golden hairy. Prominent orbicular gland on petiole.
Blade – Bipinnate. Central axis (rachis) 20-120(145) mm long, angular, furrowed, hairless or with fine hairs and have an orbicular gland where the pinnae attach (jugary glands). No interjugary glands. 3-13(15) pairs of pinnae (25)40-70(90) mm long with 15-45(50) pairs of widely spaced small leaflets (pinnules), 5-15 mm long x 0.4-1 mm wide, straight, parallel sided, pointed tip, tapering base, shiny and hairless or rarely sparsely hairy. The mid nerve is difficult to see on the upper side and visible on the lower surface.
Stems:2-10(15) m high. Erect, branched.
Branchlets are angled or flattened with wing like ridges that continue (are “decurrent”) down the petiole. Hairless or with fine sparse hairs.
New growth is hairless. Young foliage tips are yellow.
Bark – Brown to dark grey or almost black and smooth to deeply fissured longitudinally with conspicuous internodal flange marks.
Flower head:20-32 flowers in each head. 10-45 globular heads, 5-7 mm diameter, on a 60-110 mm long axillary raceme or terminal false-panicle that may be paniculate near the summit. Heads on stalks (peduncles) 3-7 mm long that are usually hairless.
Flowers subtended by a small bracteole.
Flowers:Golden to pale yellow. Bisexual. Radially symmetrical (actinomorphic). Fragrant.
Ovary – Superior. One carpel. Sparsely hairy. Numerous ovules
Style - Threadlike
Calyx – very shortly 5 lobed. Hairless or hairy (ciliate).
Petals – 5. Prominent midrib. Hairless.
Stamens - Numerous and free.
Anthers – Fertile. 2 celled. Opening by longitudinal slits
Fruit:Dark brown, reddish brown to black, broad, straight, parallel sided, flattish, smooth pod. 20-105 mm long x 4-8.5 mm wide with thickened edges and somewhat leathery. Constricted somewhat between the longitudinal seeds. Opens by two valves. Pod may be initially hairy but always becomes hairless with age.
Seeds:Short threadlike stalk (funicle) folded below the oblique thickening (aril) near the seed.
Key Characters:Adult leaves remaining bipinnate
Stipules small or none
Leaf rachis usually 6-12 cm long.
Pinnae usually 5-12 pairs.
Pinnules green, 0.5-1.5 times the length of the leaf rachis and less than 2 mm wide.
Interjugary glands absent, Jugary glands present.
Branchlets prominently winged with ridges, 0.6-2 mm high.
Flower heads globular in axillary racemes
Stamens all free, more than 10 and usually < 0.5 mm long, white, cream, yellow or orange yellow
Adapted from J.R. Wheeler, N Burbidge, J. Black, G. Harden.
Perennial tree. Seeds germinate after rain mainly in autumn and winter and especially after fire or disturbance. It grows quickly and is relatively short lived.
Flowering times:July-December in WA. Winter to early spring in SW WA.
July – December in NSW.
Summer in SA.
Late winter to spring in SE Australia.
Seed Biology and Germination:Vegetative Propagules:
Hybridises with Acacia baileyana (Burbidge and Gray, 1970).
Allelopathy:Population Dynamics and Dispersal:
Long distance spread is usually by intentional planting or movement of soil.
Origin and History:Native to NSW and possibly Victoria, naturalised in other states apart from NT.
Distribution:ACT, NSW, QLD, SA, TAS, VIC, WA.
Near Mt Lofty Ranges in SA.
Perth To Albany in WA. Swan Coastal Plain, Jarrah Forest and Warren regions.
Courtesy Australia’s Virtual Herbarium.
Habitats:Dry sclerophyll forest, often on river banks and rises.
High rainfall areas in South west WA.
Climate:High rainfall areas.
Soil:Prefers loams and heavy soils.
Ornamental garden tree.
Bark used for tanning and has a high tannin yield but less than Acacia mearnsii.
Introduced to South Africa for the tanning bark industry.
Gums, timber, honey, pollen, fibre.
Detrimental:Naturalised in WA, SA, Victoria and ACT.
Toxicity:Not recorded as toxic.
Management and Control:Picloram, Garlon® and glyphosate are used for chemical control as overall sprays, stem injection or cut stump.
Use Garlon® 480 at 1:400 or Roundup® CT at 1:200 as an overall spray for control of juvenile trees and 2 L/ha Garlon® 480 for control of seedlings.
2 L/ha of Roundup® (360 g/L) controls seedlings in autumn winter and spring but 4 L/ha was required for late summer applications.
Fire destroys the mature trees but usually leads to a mass germination of seedlings. However if these seedlings are controlled it very quickly reduces the seed bank in the soil. Seedlings tend not establish in mature stands.
A long term control plan is usually required for success.
Target areas that have been recently burnt because these will be more prone to invasion and the seed bank will be reduced due to the fire induced germination of seed.
1) In large dense stands a hot fire may be used to kill old trees and encourage seed to germinate so that it may controlled by herbicides and reduce the soil seed bank.
2) Apply herbicides in spring.
3) For mature or juvenile trees, inject the stems with 1 mL Tordon® Timber Control herbicide per 1.5 metres of height.
4) For seedlings, apply 4 L/ha of glyphosate (450 g/L) or spray until just wet with a mixture of 100 mL of glyphosate (450 g/L) per 10 L of water.
5) For juvenile trees, spray a mixture of 100 mL of glyphosate (450 g/L) plus 25 mL Pulse® Penetrant per 10 L of water onto the foliage until just wet. A concentrated mix of 1 part glyphosate with 2 parts water can also be applied using a window washer bottle. Apply about 3 mL of this solution per square metre of foliage. Lontrel®750 at 2 kg/ha may provide more selective control in some situations.
6) Avoid further burning or denuding the area as this will encourage seedling establishment.
7) Repeat the treatment every second year to ensure that no trees reach an age where they can set seed.
Some Acacia species may be more tolerant of glyphosate than others. If glyphosate is not providing adequate levels of control then use Garlon® 600 at the same rates as glyphosate above.
If felling trees, use glyphosate, Garlon®, Grazon® Access® or Tordon® Timber Control to paint the stumps immediately after felling as this species tends to sucker and coppice.
A large number of seedlings often emerge in the season after felling or burning and if these are not controlled then the infestation may become worse.
Good control can be achieved by injecting the stems with 1 mL Tordon® Timber Control herbicide per 1.5 metres of height in autumn or spring when trees are actively growing. Basal bark spraying is not usually effective on old trees with rough bark.
A large number of seedlings often emerge in the season after felling, burning or spraying. If these are left the infestation may become worse. Follow up every 2-3 years to ensure no trees reach an age where they set seed. Some Acacia species may be more tolerant of glyphosate than others. If glyphosate is not providing good control then try Garlon®, Grazon®, Hotshot®, Starane® or clopyralid(300g/L). Test various times of treatment in your area. Avoid further burning or denuding of the area as this will encourage seedling establishment.
Don’t buy or plant them in gardens outside of their native range in New South Wales and Victoria.
Herbicide resistance:None reported.
Biological Control:Unlikely because many are Australian native species.
Related plants:See the Weedy_Acacia_Key
There are more than 500 native Acacia species in WA.
Weedy and look-alike species include
Acacia Hedge (Acacia paradoxa). Noxious weed.
Black Wattle (Acacia decurrens) Bark used for tanning.
Blackwood (Acacia melanoxylon) Bark used in tanning.
Blakely's Wattle (Acacia blakelyi) Used in revegetation.
Brigalow (Acacia harpophylla)
Burrow’s Wattle (Acacia burrowii)
Caterpillar Wattle (Acacia lasiocalyx) Used in revegetation.
Cedar Wattle (Acacia elata) Ornamental
Chisholm's Wattle (Acacia chisholmii)
Coast Myall (Acacia binervia) is toxic to stock.
Cootamundra Wattle (Acacia baileyana) Ornamental
Curracabah (Acacia concurrens)
Currawong (Acacia sparsiflora)
Cutch Tree (Acacia cutechu) Noxious weed.
Deane's Wattle (Acacia deanei)
Dwarf Silver Wattle (Acacia nano-dealbata)
Flinders Ranges Wattle (Acacia iteaphylla)
Gidgee (Acacia cambagei)
Georgina Gidgee (Acacia georginae) is toxic to stock.
Golden Wattle (Acacia pycnantha) Bark used in tanning.
Golden-wreath Wattle (Acacia saligna) Used in revegetation.
Gosford Wattle (Acacia prominens) Ornamental
Green Wattle (Acacia mearnsii) Bark used in tanning.
Hop Mulga (Acacia craspedocarpa)
Manna Wattle (Acacia microbotrya) Used in revegetation.
Mimosa bush (Acacia farnesiana was Vachellia farnesiana)
Motherumbah (Acacia cheelii)
Mountain Cedar Wattle (Acacia elata)
Mulga (Acacia aneura) Used for fodder.
Prickly Acacia (Acacia nilotica). Noxious weed.
Prickly Moses (Acacia pulchella)
Queensland Silver Wattle (Acacia podalyriifolia)
Red Wattle (Acacia sylvestris)
Silver Wattle (Acacia dealbata)
Snowy River Wattle (Acacia boormanii) Ornamental
Sweet Wattle (Acacia suaveolens)
Sydney Golden Wattle (Acacia longifolia)
White Sally (Acacia floribunda)
Acacia glaucescens is toxic to stock.
Plants of similar appearance:Acacia mollissima is very similar but has more than 12 pairs of pinnae and hairy leaflets.
Acacia parramattensis is very similar but doesn’t have decurrent ridges on the petioles and is widely cultivated and adaptable.
Albizia (Paraserianthes lophantha) has broader leaflets at 1.5-3 mm wide and larger cylindric flower heads that are 3-6 cm long.
Green Wattle (Acacia mearnsii) is similar but has shorter leaflets
Silver Wattle (Acacia dealbata) is also weedy but usually has greyer or silvery leaves.
Cootamundra Wattle (Acacia baileyana) also has bipinnate leaves but they are much shorter and greyer.
Deane’s Wattle (Acacia deanei).
Karri Wattle (Acacia pentadenia) has shorter leaflets at 3-6 mm long and by the fewer (2-4) flower heads in each inflorescence.
References:Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P428. Diagram.
Bodkin, F. (1986). Encyclopaedia Botanica. (Angus and Robertson, Australia).
Burbidge, N.T. and Gray, M. (1970). Flora of the Australian Capital Territory. (Australian National University Press, Canberra). P204. Diagram P207.
Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).
Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 2. P391. Diagram.
Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (1997). Western Weeds. A guide to the weeds of Western Australia (Second Edition). (Plant Protection Society of Western Australia, Perth, Western Australia). P190. Photo.
Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #3.8.
Moore, J.H. and Wheeler, J.R. (2008). Southern Weeds and their Control. (Second Edition). Department of Agriculture and Food Western Australia. P164. Photos.
Paczkowska, G. and Chapman, A. (2000). The Western Australia flora: a descriptive catalogue. (Wildflower Society of Western Australia (Inc), the Western Australian Herbarium, CALM and the Botanic Gardens & Parks Authority). P304.
Tame, T.(1992). Acacias of Southeast Australia. Kangaroo Press, Kenthurst, NSW, Australia. P181. Diagram.
Wheeler, Judy, Marchant, Neville and Lewington, Margaret. (2002). Flora of the South West: Bunbury - Augusta – Denmark. (Western Australian Herbarium, Bentley, Western Australia). P680.
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