Mearns Black Wattle

Acacia mearnsii De Wild.

Synonyms - Racosperma mearnsii

Family: - Mimosaceae


Acacia was the name of a thorny Egyptian tree.

Mearnsii celebrates Edgar Mearns, an American naturalist who collected the type specimen.

Racosperma is Greek for ragged seed.

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.

Green Wattle because it has olive to dark green leaves and often has greenish bark and is a member of the Wattle or Acacia genus.

Other Names:

Black Wattle.


Mearns Black Wattle is a tree or shrub to 3-16 m high with black or grey bark which is usually smooth but may be rough towards the base of the trunk. The foliage is dark green. The main leaf-axis is 30-135 mm long and has 7-31 pairs of branches. Each of these branches has 25-78 pairs of small leaflets. The leaflets are 1-4 mm long and 0.5-0.8 mm wide and minutely hairy on the lower surface. The pale yellow to cream, globular flower heads are 10 mm across and arranged in 1 to 80-headed sprays. The seed pods are 3-15 cm long and 4-9 mm wide, shortly hairy, circular in cross section and quite deeply constricted between the seeds.

Native to south eastern Australia it was planted as an ornamental and also for its bark which was used in the tanning industry. It has escaped from cultivation and is now an environmental weed, flowering in spring and summer.




First leaves:



Alternate. Green to dark green and glossy on top and green underneath. Bipinnate. Main axis (rachis) 30-150 mm long. 7-31 pairs of leaflets (pinnae) 15-60 mm long. 16-78 pairs of leaflets (pinnules) 1-3.5 mm long by 0.5-0.8 mm wide, linear oblong, set close together, hairless on top and hairy underneath with an inconspicuous mid nerve. Base broadly rounded, auriculate, apex broadly rounded, truncate or obtuse. Conspicuous glands along the axis between the pinnae (jugary and interjugary).

Young foliage is yellow to greenish yellow and densely covered in velvety hairs.

Stipules - Present

Petiole - 5-25 mm long, shortly ridged, with an orbicular grey-hairy gland at base of or to 8 mm below lowest pair of pinnae. Petiole hairy but maybe bare at the base. Base of petiole swollen to form the pulvinus.

Blade of leaflet (pinnules) - Obliquely oblong, 1-3.5 mm long by 0.5-0.8 mm wide. Somewhat leathery. Tip pointed to rounded. Sides parallel, Base tapered. Hairless on top, tiny soft pale hairs underneath.

Jugary gland present and 1 interjugary gland between each pair of pinnae.


3-16 m tall. Spreading shrub or mostly erect tree

Branchlets angled, with short ridges and dense, soft pale hairs.

Bark - smooth but maybe rough on the main trunks especially at the base, greenish to blackish.

Bark of trunk smooth, corrugated at base when old, black or grey.

Flower head:

An extended paniculate raceme, 60-120 mm long with soft pale hairs at the ends of branchlets or in the axils or terminal with 10-80 pale yellow to almost white, globular heads, 10 mm diameter. 20-40 flowers in each head. Heads on stout, 5-8 mm long stalks (peduncles) that are golden hairy.

Flowers subtended by a small bracteole.


Pale yellow to almost white, less than 6 mm long. Bisexual. Actinomorphic.

Ovary - Superior. One carpel. Hairy. Numerous ovules

Style - Threadlike

Calyx - 5 short, pointed lobes. Hairy or hairless. Less than half as long as the petals.

Petals - 5. Hairless. Twice as long as the calyx.

Stamens - Numerous and free.

Anthers - Fertile. 2 celled. Opening by longitudinal slits


Dark brown to black with a waxy bloom, hairy, leathery pod, 30-150 mm long by 4-9 mm wide, circular in cross section, straight to slightly curved and usually constricted between the seeds. Hairy and slightly rough to touch. Seeds arranged longitudinally in the pod. Opens by two valves


Short seed stalk (funicle) expanded towards the seed (obliquely arilate).



Key Characters:

Mature leave bipinnate, phyllodes never produced.

Branchlets distinctly hairy, not or rarely slightly pruinose.

Leaves green, bipinnate with more than 6 pairs of pinnae

Pinnules 2-4 mm long and <2 mm wide, linear to oblong, hairy, upper surface green and lower surface paler.

Jugary and Interjugary glands present.

Flower heads on extended axillary or terminal racemes or panicles.

Flowers actinomorphic.

Ovary superior.

Stamens all free, more than 10 and usually < 0.5 mm long, white cream, yellow or orange yellow

Adapted from G. Harden, N. Burbidge, J.R. Wheeler.


Life cycle:

Perennial. Grows rapidly.



By seed.

Flowering times:

February in WA.

October to December in NSW.

Summer in SE Australia.

Mainly October to December in Australia.

September to November in NZ.

Seed Biology and Germination:

Vegetative Propagules:



Population Dynamics and Dispersal:

Long distance spread by intentional planting mainly as an ornamental but previously for bark production used in tanning. Medium distance spread mainly by movement of seed infested soil. Local spread by seed distribution.

Origin and History:

Native of South Eastern Australia.

In the late 1800's and early 1900's it was planted for bark used in tanning.



Swan Coastal Plain and Jarrah Forest regions of WA.

New Zealand.

Courtesy Australia's Virtual Herbarium.


River banks, ridges, swampy flats, scrubland, open forest, woodland disturbed areas, grasslands in gullies or on hillsides.


Cool temperate, Mediterranean.


Prefers gravelly clay, black peaty soil, brown sandy clay and heavy soils but also grows on sands.

Plant Associations:

Dry sclerophyll forest. Eucalypt forests and woodlands.




Bark was used for tanning.


Environmental weed.


Not recorded as toxic.





Management and Control:

Picloram, Garlon and glyphosate are used for chemical control as overall sprays, stem injection, cut stump or topical application to trunk.

Use Access in diesel at 1:60 and paint or spray the lower 50 cm of trunk. Make sure the herbicide is applied all the way around the trunk or the untreated side of the tree may survive.

Use Garlon 480 at 1:400 and 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.

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 by regenerating trees, suckers and seedlings. The seed bank will also be reduced due to the fire induced germination of seed.


Eradication strategies:

In large dense stands, a hot fire may be used to kill old trees and encourage seed to germinate.

Cutting at the base, ringbarking or bulldozing old trees and hand pulling seedlings provides good control.

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 sprays are not as effective due to the rough bark on old trees. On younger trees with smooth bark use a mixture of 1 L of Access® in 60 L of diesel and apply to the lower 50 cm of the trunk and repeat in 6 months if necessary.

Trees less than 2 m tall can usually be controlled by spraying the leaves until just wet with a mix of 100 mL glyphosate(450g/L) plus 25 mL Pulse in 10 L water. 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.

Seedlings can be controlled with 4 L/ha glyphosate(450g/L).

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. Avoid further burning or denuding of the area as this will encourage seedling establishment.

Replant area with endemic seedlings.

Don't buy or plant them in gardens outside their native range in south eastern Australia.

Herbicide resistance:

None reported.

Biological Control:

Unlikely because it is an Australian native species.

Related plants:

See A key for weedy Acacias and similar native species

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)

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)

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:

Albizia (Paraserianthes lophantha) has larger leaflets at 5-10 mm long by 1.5-3 mm wide and large cylindric flower heads that are 30-60 mm long.

Black Wattle (Acacia decurrens)

Karri Wattle (Acacia pentadenia) has larger leaflets at 3-6 mm long and fewer (2-4) flower heads per leaf axil.

Silver Wattle(Acacia dealbata) has whitish yellow young leaves and no interjugary glands and flowers earlier.

Acacia constablei tends to have no interjugary glands and flowers earlier.


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 P209.

Harden, Gwen J. (1991). Flora of NSW. (Royal Botanic Gardens, Sydney). Volume 2. P390. 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.

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. P166. 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. Photo

Tame, T.(1992). Acacias of Southeast Australia. Kangaroo Press, Kenthurst, NSW, Australia. P186. Diagram.


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