Kangaroo Thorn (Acacia paradoxa) is a straggly to compact, intricate spiny shrub or small tree 2-4 m high with dark brown finely fissured bark, weeping branches and ribbed branchlets. The leaves are replaced by undivided leaf-like phyllodes that are 8-20(30) mm long by 2-8 mm wide, shortly hairy with wavy margins and each face has 1 prominent longitudinal vein (the non-central midrib). Two spines occur at the base of each phyllode and are 4-15 mm long. The globular golden flower heads are single (or rarely 2) per axil. The seed pods are 2-7 cm long and 3-5 mm wide, straight to slightly curved and shortly hairy.
Native to eastern Australia and planted as an ornamental or hedge species, it is now a weed often forming dense thickets in high rainfall areas especially after fires. It flowers from July to October.
Alternate. On mature plants there are no true leave and only green leaf like phyllodes which are flattened petioles.
Phyllodes: Erect, asymmetrical, egg shaped to spear shaped, straight or slightly curved, flat, erect, 7-20(30) mm long by 2-8 mm wide and often somewhat crowded. Upper edge undulating. Mid vein prominent and off centre and side veins branching. Edges slightly thickened and undulating. One small gland near base of “leaf”. Tip pointed which may be hard or soft or acute with a fine, curved, pungent point (mucro) or beaked. Edges curved and undulating. Base asymmetrically tapered. Initially hairy and becoming hairless with age apart from hairs on the central vein.
Stipules - 2 persistent, rigid spines mostly 4-12(15) mm long.
Petiole - Base of petiole swollen to form the pulvinus which is 0.5 mm long and often hairy.
Blade - None on mature trees, bipinnate on juvenile foliage.
2-4 m tall often with drooping outer branches. Usually hairy.
Erect or spreading. Many branched. Branches are sometime drooping or weeping.
Branchlets angled or ribbed (or occasionally cylindrical lower down) and usually hairy but occasionally almost hairless.
Bark - Dark brownish grey and finely fissured.
Very bright yellow, globular flower heads, 7-12 mm diameter that are borne singly (or rarely in pairs) in the leaf axils on hairless to sparsely hairy stalks (peduncles) that are 5-15(20) mm long (as long as the leaf). Each head has (20)30-50 tiny flowers.
Flowers subtended by a long, spiny bracteole that is conspicuous in bud.
Ovary - Superior. One carpel. Hairy to hairless. Numerous ovules
Style - Threadlike
Calyx - 5 lobed that separates into spade shaped sepals. Hairy.
Sepals - 5. Spade shaped and united.
Petals - 5. Hairless.
Stamens - Numerous and free.
Anthers - Fertile. 2 celled. Opening by longitudinal slits
Light brown, cylindrical, straight or slightly curved, flattish pod, 20-60(70) mm long by 3-5 mm diameter. Thinly leathery. Scarcely constricted between the seeds. White hairy and somewhat sticky. Edges pale and thickened. The seeds are arranged longitudinally on the pod. Opens by two valves
Green to dark brown, elliptical, 3-5 mm long by 2 mm, shiny.
Funicle thread like and expanded near the seed to a prominent pale, small aril.
Phyllodes 3-7 mm wide and 8-30 mm long (< 6 times as long as broad) with a distinct mid vein and conspicuous? lateral or reticulate veins.
Phyllodes undulate, asymmetrical, mid vein off centre.
Phyllodes with ending in a short mucro.
Stipules persistent, spines 5-15 mm long.
Flower heads globular, golden yellow and on simple axillary peduncles
Flowers actinomorphic, 5 merous, more than 15 per head.
Stamens all free, more than 10 and usually < 0.5 mm long, white cream, yellow or orange yellow
Adapted from J.R. Wheeler, G Harden.
August to October in Perth. July to October in WA.
July to November in NSW.
Spring in Western NSW.
Spring in SE Australia.
Seed Biology and Germination:
Germinates readily after fire.
Hybridises with a number of other Acacia species
Population Dynamics and Dispersal:
Increases rapidly after fire.
Long distance dispersal usually by intentional plantings as a hedge plant.
Origin and History:
Native to south eastern Australia.
Introduced to Tasmania and Western Australia.
ACT, NSW, QLD, SA, TAS, VIC, WA.
Avon Wheatbelt, Esperance Plains, Jarrah Forest, Swan Coastal Plain and Warren regions of WA.
Naturalised in Tasmania.
Courtesy Australia's Virtual Herbarium.
Mugga Ironbark, Green Mallee, Grey Box and many other plant communities.
Dry hillsides in Tasmania (Curtis, 1956).
Cool temperate, Mediterranean.
Grows on a range of soil types.
Prefers gravelly and stony ridges, white-grey sands, clay, rocky loam, wet areas, heavy soils.
Tuart forest, Mugga Ironbark, Green Mallee, Grey Box. Woodlands and shrublands
Hedge plant. Ornamental. Shelter.
Environmental weed forming dense thickets in high rainfall areas especially after fire.
Suspected of poisoning stock (Webb, 1948), however the spiny nature of the plant generally precludes grazing and stock poisoning is rare.
Remove stock from infestation or provide alternate feed.
Was a noxious weed of Victoria.
Management and Control:
Picloram, Garlon and glyphosate are used for chemical control as overall sprays, cut stump or topical application to the trunk.
Use Garlon 480 at 1:400 and Roundup CT at 1:200 as an overall spray for control of juvenile shrubs 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 shrubs 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.
In large dense stands a hot fire may be used to allow better access for control and encourage seed to germinate so that it may be controlled by herbicides and reduce the soil seed bank.
Cutting at the base, bulldozing, root raking and hand pulling seedlings (with gloves) provides good control.
A basal bark treatment is often the most cost effective. Apply a mixture of 1 L of Access® in 60 L of diesel to the lower 50 cm of the trunk and repeat in 6 months if necessary.
For mature or juvenile shrubs, apply a mixture of 1 L of Grazon in 100 L of water to the foliage any time the plant is 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.
For juvenile shrubs, 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.
Avoid further burning or denuding the area as this will encourage seedling establishment.
Repeat the treatment every second year to ensure that no plants reach an age where they can set seed.
A large number of seedlings often emerge in the season after dozing, burning or spraying. If these are left the infestation may become worse. Follow up every 2-3 years to ensure no plants 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.
Don't buy plant them in gardens outside of their native range in south eastern Australia.
Unlikely because many are Australian native species.
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.
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.
Plants of similar appearance:
Prickly Moses (Acacia pulchella) a WA native species.
Distinguished from Acacia congesta and Acacia idiomorpha by its innocuous phyllodes.
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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. P366. 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.
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Marchant, N.G., Wheeler, J.R., Rye, B.L., Bennett, E.M., Lander, N.S. and Macfarlane, T.D. (1987). Flora of the Perth Region. (Western Australian Herbarium, Department of Agriculture, Western Australia). P227.
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. P170. 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). P318.