Golden Wattle

Acacia pycnantha Benth.

Family: Fabaceae (was Mimosaceae)

Names:

Acacia was the name of a thorny Egyptian tree.
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.
Pycnantha refers to the dense flower heads.
Golden Wattle; refers to its flower colour and it is in the wattle or Acacia genus.

Other names:

Broad-leaved Wattle because its leaves are much broader than most wattles.
Black Wattle
Green Wattle
Witch

Summary

Golden Wattle (Acacia pycnantha) is Australia's floral emblem. It is a loosely branched shrub or tree 3-8 m high with dark brown to grey smooth bark and dark green foliage. The leaves are replaced by pendulous, undivided leaf-like phyllodes that are 60-200 mm long x 5-35(50) mm wide, curved and asymmetric with a blunt tip, leathery, hairless and each face with only 1 prominent longitudinal vein (midrib). It has 1 or 2 glands on the phyllode. The sweetly scented, golden globular flower heads are arranged in showy sprays of 6-20 heads, each head with 40-80 flowers and a thick stalk 3-6 mm long. The seed pods are brown, flat, 50-130 mm long and 5-7 mm wide, hairless, thick and fairly straight. Native to eastern Australia Golden Wattle has become a common weed of roadsides, sometimes invading bushland. It flowers from July to October.

Description:

See the Weedy_Acacia_Key

Cotyledons:

Two.

First leaves:

Young leaves are bipinnate (leaves with leaflets that have leaflets) and are present on seedlings. They then develop into phyllodes, which are flattened leaf like petioles (leaf stalks). Hairless.

Leaves:

Alternate. On mature plants there are no true leave and only dark green phyllodes which are flattened petioles.
Phyllodes: (60)90-150(200) mm long x (5)10-35(50) mm wide, flat, lance shaped (to slightly egg shaped on lower leaves), leathery and pendulous. Usually somewhat curved with 1 obvious, lengthwise mid vein with branched side veins and nerve like margins that are sometimes thickened. The phyllodes are narrowed toward their asymmetric base. Tip rounded or pointed. Sides curved. Base tapered. Hairless. 1-2 glands on the edge of the phyllode with one near the base (3-45 mm above the pulvinus) and occasionally the a second one more than half way along the phyllode. The pulvinus, which moves the leaf by changes in pressure, is 4-8 mm long at the base of the phyllode.
Stipules - Fall off before the phyllode matures.
Petiole - Flattened and looks like a leaf.
Blade - None on mature trees, bipinnate on juvenile foliage.

Stems:

Erect or spreading tree or shrub. Branched. Single or several stems from the base. (1)3-8 m tall. Branchlets angled or cylindrical and usually hairless.
Bark grey to brownish, smooth or finely fissured.
Bark of upper trunk and main branches usually pale with a whitish bloom.
Will coppice or regrow if damaged.

Flower head:

Golden yellow, large, with 6-20 dense, showy, globular clusters, 4-8 mm wide and of (30)40-80 small flowers along robust, waxy, stout, hairless and an often curved or zig-zag axis (rachis) 25-90(150) mm long (shorter than the phyllodes) and arise from the axil or at the ends of branches. Each globular cluster is on a 2-10 mm stalk(peduncle) that is stout and usually hairless.
Small, <0.5 mm, sub circular, brown to blackish bracts with white fringes are obvious when in bud

Flowers:

Many fragrant individual flowers on 2-5 mm stalks.
Ovary - Furry
Calyx - More than half as long as the corolla with 5 short, acute, lobes with fine tufted hairs.
Petals - 5. Hairless.
Stamens - Many, free.
Anthers -

Fruit:

Almost straight, narrow, slightly leathery, light brown pod, 50-130(140) mm long, 5-7(8) mm wide, slightly wrinkled, hairless. Flattish but convex over the lengthwise seeds and slightly constricted between the seeds.

Seeds:

Black, elliptical, 5-6 mm long x 3 mm wide and shiny. Seed stalk(funicle) shorter than the seed and almost straight alongside it and is thickened upwards into a fleshy, pale aril where it joins the seed.

Roots:

Taproot.

Key Characters:

Adult leaves are phyllodes.
Juvenile leaves bipinnate and not persistent on the adult.
Phyllodes flat, broad-lanceolate, usually curved, rigid with nerve like margins, 60-200 mm long and less than 20 times longer than wide, 1 obvious central vein. Usually strongly asymmetric at the base.
Phyllodes tapered into a 5-8 mm long pulvinus.
No mucro on phyllodes. Not pungent tipped.
Young flower heads not enclosed in large bracts.
Axillary racemes of 6-20 globular heads with many flowers.
Flowers regular (actinomorphic)
Flowers in globular heads with 40-80 flowers.
Flower heads on stout peduncles.
Rachis robust, often flexuose
Petals valvate
Stamens free, many.
Pod straight edged, 50-140 mm long x 5-8 mm wide.
Seeds longitudinal in pod.
Funicle shorter than the seed.
Embryo straight.

Adapted from John Black, Nancy Burbidge, Gwen Harden and Judy Wheeler.

Biology

Life cycle:

Perennial, tree or spreading shrub up to 8 m high. The main flowering period is June to October. Seedlings germinate in winter producing acacia type juvenile leaves (many leaflets arranged like a feather) for the first season or two. The juveniles quickly grow to maturity to start producing seed at about 3 years old and become prolific producers of pods and seeds. Often they grow individually but sometimes thickets are formed and few species grow in the understorey. Fire or denudation may kill older trees and this leads to a massive germination of fast growing seedlings that out compete many other plants. Stems will coppice or regrow if damaged. Relatively short lived.

Physiology:

Frost sensitive.

Reproduction:

By seed.

Flowering times:

August to October in Perth.
Winter and spring in SW of WA
September to October in SA.
Spring in Western NSW and SE Australia.
July to November in NSW.

Seed Biology and Germination:

Seed has significant dormancy and will last in the soil for many years.
Many seeds germinate after fire.

Vegetative Propagules:

Tends to coppice when damaged.

Hybrids:

Ecology, Population Dynamics and Dispersal:

Spread by seeds.
Seeds spread by birds, water flows, soil movement and garden refuse.
Increases in density usually following denudation events.

Origin and History:

Australia. Native to the eastern states and introduced to South Australia, Tasmania and Western Australia where it is spreading rapidly.

Distribution:

ACT, NSW, SA, TAS, VIC, WA.
Weed in South Africa.

Courtesy Australia's Virtual Herbarium.

Habitats:

Climate:

Temperate. Moderate to high rainfall areas. Prefers hot, low humidity areas.

Soil:

Prefers red loams, sandy and stony soils and disturbed areas.

Plant Associations:

Dry sclerophyll forest and heath. White Cypress Pine, Yellow Box, Grey Box, Bull Oak, Eucalypt forests, Callitris forests.

Significance:

Beneficial:

Used for gum, timber, fuel wood, fibre, aboriginal food, herbal medicine, ornamental and shelter trees. The bark is one of the richest sources of tannin (used for tanning) in the world and was once used commercially for tannin extraction.
Tough close grained timber. The gum is eaten by aborigines.
Planted as windbreaks and sometimes distributed in packets of free seed provided by revegetation organizations.

Detrimental:

Invasive weed in WA and South Africa.
In higher rainfall zones it tends to have a thin stemmed habit and forms thickets excluding other plants.

Toxicity:

Symptoms:

Treatment

Legislation:

None

Management and Control:

Picloram, Garlon® and glyphosate are used for chemical control as overall sprays, stem injection, cut stump or topical application to trunk.
Fire may destroy mature trees but tends to induce a mass germination of seedlings. If these seedlings are controlled it reduces the seed bank in the soil. Seedlings do not readily establish in mature stands.
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.

Thresholds:

Eradication strategies:

Odd large trees may be felled and the cut stump immediately painted with neat glyphosate or 1:60 Access® in diesel to prevent regrowth.
In large dense stands a hot fire may be used to allow better access and encourage seed to germinate so that it may controlled by herbicides and reduce the soil seed bank.
For mature or juvenile trees, apply a mixture of 1 L of Access® in 60 L of diesel to the lower 500 mm of the trunk or inject the stems with 1 mL Tordon® Timber Control herbicide per 1.5 metres of height. Autumn is probably the best time to apply and repeat in 6 months if necessary.
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 in spring.
For juvenile trees, spray a mixture of 100 mL of glyphosate (450 g/L) (or 25 mL Garlon480) plus 25 mL Pulse® Penetrant per 10 L of water onto the foliage until just wet in spring. 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.
Avoid further burning or denuding the area as this will encourage seedling establishment.
Repeat treatment every second year to ensure that no trees reach an age where they can set seed.
Use glyphosate, Garlon®, Grazon® Access® or Tordon® Timber Control to paint the stumps immediately after felling or inject herbicide into the trunk as this species tends to coppice or sucker after being damaged.
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.
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.
Don't buy or plant them in gardens outside of their native range which is Victoria and southern NSW.

Herbicide resistance:

None reported.

Biological Control:

Biocontrol is unlikely because it is an Australian native plant.

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.
Racosperma species.

Plants of similar appearance:

Golden Wreath Wattle (Acacia saligna) has slightly narrower and acute 'leaves' with a shorter pulvinus, less (2-20) heads in each shorter spray of flowers and its seed pods have thickened, pale edges. It is native to WA.
Myrtle Wattle (Acacia myrtifolia) has shorter more erect phyllodes 20-130 mm long, cream to pale yellow flower heads with very few flowers (2-5) per head and each flower has only 4 sepals and 4 petals.
Acacia leiophylla
Acacia obliquinervia
Acacia pedina from the South Coast of N.S.W. has straight to shallowly recurved, oblanceolate to obovate adult phyllodes, large juvenile and intermediate phyllodes and 25-40-flowered heads.
Acacia penninervis is very similar but has fewer flowers in the heads.
Acacia retinodes is almost identical and can often only be distinguished on the seed characters.

References:

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P414. Diagrams.

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). P200. Diagram.

Cunningham, G.M., Mulham, W.E., Milthorpe, P.L. and Leigh, J.H. (1992). Plants of Western New South Wales. (Inkata Press, Melbourne). P370. Photo.

Everist, S.L. (1974). Poisonous Plants of Australia. (Angus and Robertson, Sydney).

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Vol 2, P382-383. 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. (Plant Protection Society of Western Australia, Perth, Western Australia). P180. Photo.

Lamp, C. and Collet, F. (1990). A Field Guide to Weeds in Australia. (Inkata Press, Melbourne).

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #3.23.

Maslin, B.R. (2001) Wattle. Acacias of Australia. CD.

Moore, J.H. and Wheeler, J.R. (2008). Southern Weeds and their Control. (Second Edition). Department of Agriculture and Food Western Australia. P172. Photos.

Marchant et al (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P228.

Tame, T.(1992). Acacias of Southeast Australia. Kangaroo Press, Kenthurst, NSW, Australia. P127. Diagram.

Acknowledgments:

Collated by HerbiGuide. Phone 08 98444064 or www.herbiguide.com.au for more information.