paradoxa DC.][Bayer code: none][CDFA list: B] Photographs
Map of Distribution
Black acacia [Acacia
melanoxylon R.Br.][Bayer code: none] Photographs
DESCRIPTION:Acacias are grown as woody ornamentals and not typically
weedy, but a few species have escaped cultivation in some coastal
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leaves even 2-pinnate compound.
are actually simple, leaf-like phyllodes (expanded petioles).
Phyllodes alternate, lanceolate to oblong, evergreen, leathery.
and UNDERGROUND STRUCTURES:Usually associated with nitrogen-fixing bacteria.
8-10 mm diameter, consist of 30-50 flowers. Stamens separate,
exserted, > 10 per flower. Petals, sepals inconspicuous.
and SEEDS:Pods split open along both margins. Seeds attach
to pod with a long, folded stalk.
usually near cultivated plants.
Bay region, western South Coast Ranges, South Coast. To 200 m
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.
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
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.