Kangaroothorn [Acacia paradoxa DC.][Bayer code: none][CDFA list: B] Photographs Map of Distribution

Black acacia [Acacia melanoxylon R.Br.][Bayer code: none] Photographs

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GENERAL DESCRIPTION:Acacias are grown as woody ornamentals and not typically weedy, but a few species have escaped cultivation in some coastal regions.

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SEEDLINGS:Juvenile leaves even 2-pinnate compound.

MATURE PLANT:Leaves are actually simple, leaf-like phyllodes (expanded petioles). Phyllodes alternate, lanceolate to oblong, evergreen, leathery.

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ROOTS and UNDERGROUND STRUCTURES:Usually associated with nitrogen-fixing bacteria.

FLOWERS:Round heads 8-10 mm diameter, consist of 30-50 flowers. Stamens separate, exserted, > 10 per flower. Petals, sepals inconspicuous.

FRUITS and SEEDS:Pods split open along both margins. Seeds attach to pod with a long, folded stalk.

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HABITAT:Disturbed areas, usually near cultivated plants.

DISTRIBUTION:San Francisco Bay region, western South Coast Ranges, South Coast. To 200 m (650 ft).

PROPAGATION/PHENOLOGY:Reproduce by seed. Seeds typically disperse near the parent plant or to greater distances by human activities or water. Seed is hard-coated and requires scarification or degradation to germinate. Seed is probably long-lived, but longevity is undocumented. Pods and seeds are not utilized by native wildlife.

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SIMILAR SPECIES:There are at least 11 other Acacia species that occasionally escape cultivation in California. The following 4 species are more widespread or likely to be problematic. Unlike kangaroothorn and black acacia, they lack phyllodes and have even 2-pinnate compound leaves with more than 2 pairs of pinnae (first divisions of 2-pinnate leaves) at maturity. Flowers are in bright yellow heads and spines are absent, except where noted. For a quick comparison, refer to the table Comparison of selected Acacia species. In addition, the mesquites [Prosopis spp.] are distinguished by having 10 stamens per flower and 1-2 pairs of pinnae.

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Prevention: Kangaroo thorn is a spreading, prickly shrub 2-3 m high and 3-4 m across. It is native to the temperate regions of Australia and has been used in ornamental and hedgerow plantings. It was likely introduced to California for the same purposes. Little is known regarding the biology of kangaroo thorn. Established plants are long-lived and are able to tolerate drought and frost. Seed are produced in pods that burst open in dry, warm conditions. Seed may be spread by vehicles, humans, and possibly animals. In California, kangaroo thorn has spread by ornamental and hedgerow plantings. Kangaroo thorn should be replaced with native California shrubs native to the infested areas.

Mechanical: Physical removal of plants has been an effective control method. Plants must be cut or pulled below the soil surface. This may be accomplished by chaining, dozing or sawing. To prevent seed dispersal, plants should be removed before fruiting pods are produced. There will likely be a seedling flush following removal of mature plants. First year seedlings may be controlled with mowing before becoming established.

Biological: There are no registered biocontrol agents for kangaroo thorn. However, grazing with goats has been effective in controlling smaller plants. It is unknown whether seed viability is retained through animal digestive systems. Therefore, animals grazing in infested areas during pod production should be held prior to moving to other areas.
Kangaroo thorn seedling growth is generally slow in the first year. The establishment of competitive vegetation will reduce but not eliminate seeding recruitment. Areas where physical removal has been utilized should be replanted with desired vegetation. Otherwise, reinvasion by kangaroo thorn or other weeds is highly probable.

Chemical: Where chemical control is an option, triclopyr and clopyralid have been effective for controlling kangaroo thorn. Both should be applied as a foliar treatment when plants are actively growing. An integrated approach of physical removal of large plants followed by a herbicide treatment of new seedlings is effective and reduces competition for grass establishment.

Lane, D. and K. Turnbull. 1979. The significance of noxious weeds on roadsides in agricultural
areas of Victoria, Australia. Weed Research 19:151-156.
Parsons, W.T. and E.G. Cuthbertson. 1992. Noxious weeds of Australia. Inkata Press,
Melbourne and Sidney. pp. 439-440.

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