Blackwood

Acacia melanoxylon R.Br.

Synonyms - Racosperma melanoxylon

Family: Fabaceae (was Mimosaceae)

Names:

Acacia was the name of a thorny Egyptian tree.
Melanoxylon means black wood.
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.
Blackwood refers to the dark timber and is the translation of the species name.

Other Names:

Hickory
Mudgerabah
Sally Wattle
Tasmanian Blackwood (NZ)

Summary:

Blackwood (Acacia melanoxylon) is a large tree to 6-30(45) m high or a dense shrub 1.5-3 m high with dark grey fissured bark and dark green foliage. The leaves are replaced by undivided leaf-like phyllodes that are 4-16 cm long and 6-25 mm wide, often asymmetrical or somewhat curved and each face has 3-5 prominent longitudinal veins and network veins in between. The globular cream flower heads are 5-7 mm across and in short sprays of 3-5 heads arising from the axils. The seed pods are up to 15 cm long x 3-8 mm wide and are coiled and twisted. Each seed is encircled by a bright pink or red stalk.
Native to eastern Australia, Blackwood is a troublesome weed of swamps between Augusta and Albany. It may form dense thickets after disturbance and flowers in spring.

Description:

See the Weedy_Acacia_Key

Cotyledons:

Two.

First leaves:

Bipinnate leaves often persist on young plants.

Leaves:

Alternate. On mature plants there are no true leave and only green leaf like phyllodes which are flattened petioles.
Phyllodes: Dark green and somewhat leathery. Narrowly oblong to spear shaped, sometimes slightly curved, 40-160 mm long x 6-25(30) mm wide, usually with 3-5(7) longitudinal nerves on each face and many reticulating veins. The nerve islands are almost rectangular. 1 gland near the base. Rounded to pointed tip sometimes with a tiny, curved point (mucro), curved sides, tapering base. Generally hairless but often tiny hairs towards the base.
In WA the “leaves” are more curved than in the eastern states (see diagram).
Stipules - Present
Petiole - Hairless. Base of petiole swollen to form the pulvinus that is 2-4 mm long.
Blade - None on mature trees, bipinnate on juvenile foliage.

Stems:

There are tree forms that are 6-30(45) m tall and shrub forms which are 1.5-3 m tall.
Hairless apart from young shoots.
Branchlets angular or flattened near the tip and rounder below with conspicuous ribs. Young branchlets sometimes hairy and become hairless with age.
Bark - Dark grey to black, hard, deeply fissured longitudinally and somewhat scaly.

Flower head:

Pale yellow to almost white with 30-56 flowers. (2)3-5(8) globular heads, 6 mm diameter on hairy or hairless stalks (peduncles) that are 4.5-13(20) mm long and in axillary sprays (racemes) on a 6-40(80) mm long axis and much shorter than the phyllodes.
Main axis (rachis) has tiny hairs.
Flowers subtended by a small bracteole.

Flowers:

Pale yellow to almost white.
Bisexual. Actinomorphic.
Ovary - Superior. One carpel. Hairy to hairless. Numerous ovules
Style - Threadlike
Calyx - Shortly 5 lobed, hairy. More than half as long as the petals. Sepals united for ¾ of their length or more.
Petals - 5. Striped. Hairless.
Stamens - Numerous and free.
Anthers - Fertile. 2 celled. Opening by longitudinal slits

Fruit:

Parallel sided, biconvex to flattish, often twisted, curled or coiled, brown pod, 40-150 mm long x 3.5-8(10) mm wide with thickened edges. Pods leathery to woody and hairless. Nerve like edges on pod. Distinct longitudinal veins on pod. Seeds placed longitudinally in the pod. Pod opens by two valves that have reticulate markings.

Seeds:

Black, 3-5 mm long, broadly elliptical and shiny
Seed stalk (funicle) is pink to orange-red, thick, fleshy and encircles the seed in a double fold. Small swelling (aril) where the seed stalk joins the seed.

Roots:

Taproot and laterals that may form suckers.

Key Characters:

Phyllodes with 3-7 nerves with a fine reticulation of veinlets between.
Phyllode flat, not pungent and with marginal gland near pulvinus.
Pulvinus > 2 mm long.
Branchlets distinctly angled and hairless.
2-4 globular heads in short axillary racemes.
Calyx 5 lobed.
Flowers pale yellow and actinomorphic.
Ovary superior.
Stamens all free, more than 10 and usually < 0.5 mm long, white, cream or yellow.
Pods with distinctive longitudinal veins.
Seed longitudinal in pod.
Seed encircled by double fold of bright red funicle.
Adapted from J.R. Wheeler, J. Black, N Burbidge, G. Harden.

Biology:

Life cycle:

Perennial. Long lived.

Physiology:

Reproduction:

By seed and root suckers.

Flowering times:

August to October in WA.
September to October in SA.
Spring in the ACT.
July to December usually in NSW.
Late winter to spring in SE Australia.

Seed Biology and Germination:

Vegetative Propagules:

Suckers from the roots.

Hybrids:

Allelopathy:

Population Dynamics and Dispersal:

Long distance spread is by intentional planting or dumping of garden refuse. Short distance spread is by seed and suckering from the roots.
Medium distance spread is by birds attracted to the bright orange-red funicle surrounding the seed.

Origin and History:

Native to NSW, Queensland, SA, Tasmania and Victoria.
First collected by Robert Brown from Port Dalrymple in Tasmania in 1804.

Distribution:

ACT, NSW, QLD, SA, TAS, VIC, WA.
New Zealand.
In the Swan Coastal Plain, Jarrah Forest and Warren regions of south west WA.

Courtesy Australia's Virtual Herbarium.

Habitats:

Gullies and cool slopes.
Wet sclerophyll forest and cooler rainforest.
Seasonal forest swamplands in Tasmania.

Climate:

Mediterranean, cool temperate

Soil:

Gravelly laterite soils and loams. Clayey and basaltic soils. Favours fertile soils in valleys and on flats in mountainous areas.

Plant Associations:

Sclerophyll forest.
Karri.

Significance:

Beneficial:

Ornamental.
High quality, dark timber used for furniture making, panelling and stringed instruments.
Gums, fuel, lumber

Detrimental:

Environmental weed spreading in high rainfall areas and difficult to control due to its regrowth from suckers, fast growth rates and spread by seed.
Forms dense thickets in disturbed and wet areas.
Environmental weed of South Africa.

Toxicity:

Not recorded as toxic.

Symptoms:

Treatment:

Legislation:

None.

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.

Thresholds:

Eradication strategies:

In large dense stands a hot fire may be used to allow easier access and encourage seed to germinate so that it may controlled by herbicides and reduce the soil seed bank. It will regenerate profusely from suckers and seed after fire.
For mature or juvenile trees, inject the stems with 1 mL Tordon® Timber Control herbicide per 1.5 metres of height in autumn or spring when trees are actively growing.
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 any time they are actively growing.
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 in autumn or spring when trees are actively growing. 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 the treatment every year to ensure that no trees reach an age where they can set seed.
This species suckers profusely which makes mechanical control difficult without the aid of herbicides.
Use glyphosate, Garlon®, Grazon® Access® or Tordon® Timber Control to paint the stumps immediately after felling or inject herbicide into the trunk.
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 in eastern Australia and Tasmania.
In commercial plantings implement strategies to prevent escape.

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.
Acacia jucunda
Racosperma species.

Plants of similar appearance:

Coastal Wattle or Red-eyed Wattle (Acacia cyclops) has seeds with a similar red to orange encircling seed stalk and similar phyllodes but its inflorescences are reduced to 2 golden yellow flower heads per axil.
Acacia frigescens has similar foliage and habit.
Acacia implexa is very similar, with the main differences in the phyllodes and seed and it has hairy branchlets and a white funicle that doesn't encircle the seed.
Acacia oraria has broader pods and is scurfy on its branchlets, phyllodes and inflorescences, especially when they are young.
Acacia saligna
Acacia pycnantha

References:

Auld, B.A. and Medd R.W. (1992). Weeds. An illustrated botanical guide to the weeds of Australia. (Inkata Press, Melbourne).

Black, J.M. (1965). Flora of South Australia. (Government Printer, Adelaide, South Australia). P420. 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). P202. Diagram.

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

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. P361. Diagram.

Hussey, B.M.J., Keighery, G.J., Cousens, R.D., Dodd, J. and Lloyd, S.G. (2007). Western Weeds. A guide to the weeds of Western Australia. (Second Edition) Plant Protection Society of Western Australia, Perth, Western Australia. P192. Photo.

Lazarides, M. and Cowley, K. and Hohnen, P. (1997). CSIRO handbook of Australian Weeds. (CSIRO, Melbourne). #3.17.

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. P169. 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). P315.

Roy, B., Popay, I., Champion, P., James, T. and Rahman, A. (1998). An Illustrated Guide to Common Weeds of New Zealand. (New Zealand Plant Protection Society). P169.

Wheeler, Judy, Marchant, Neville and Lewington, Margaret. (2002). Flora of the South West: Bunbury - Augusta - Denmark. (Western Australian Herbarium, Bentley, Western Australia). P670. Diagram.

Tame, T.(1992). Acacias of Southeast Australia. Kangaroo Press, Kenthurst, NSW, Australia. P64-65. Diagram.

Acknowledgments:

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