Form: shrub — perennial
Status: not known to be present in WA, if found please report
Native to tropical America. Mimosa pigra is a Weed of National Significance (WoNS).
An erect, much-branched prickly shrub, which can grow to a height of three to five metres. Reproduces from seeds and suckers. Capable of forming large dense thickets, as seen in parts of the Northern Territory, most notably on the Adelaide River’s flood plain.
Stems: Greenish at first becoming woody, to three metres long, initially covered with short stiffened hairs, and bearing randomly scattered hooked prickles 5–10 millimetres long.
Leaves: Bright green 20–25 centimetres long, bipinnate, consisting of about 15 pairs of opposite primary segments five centimetres long, each with numerous pairs of stalkless narrow leaflets that fold when touched or injured. Pairs of prickles sometimes occur between the branchlets on the main leaf stalk.
Flowers: Numerous, small pink or mauve flowers grouped into globular heads one to two centimetres diameter; heads borne on stalks two to three centimetres long, two in each leaf axil, petal tube four lobed with eight pink stamens.
Fruit: A thickly hairy flattened pod borne in groups in the leaf axils, each to 6.5–7.5 centimetres long and 7-10 millimetres wide each bearing 20–25 seeds, turning brown when ripe and breaking into one-seeded segments.
Seed: Brown or olive green, oblong, flattened four to six millimetres long and two millimetres wide.
Root: Branched woody tap root, to two metres long, bearing nitrogen-fixing nodules amongst the fine feeding roots.
Agricultural and economic impact
Can form dense monocultures and causes problems for the cattle industry in particular, also an environmental weed of wetlands.
Economic modelling indicates that mimosa would cost Western Australia $6.0 million each year if it is not managed and $2.3 million if it is managed (Cook, D., 2014. Agricultural Resource Risk Management. Strategic Report. Impact Assessments for Declared Plants in Western Australia. Department of Agriculture and Food WA)
Declared pest category
The Western Australian Organism List (WAOL) contains information on the area(s) in which this pest is declared and the control and keeping categories to which it has been assigned in Western Australia (WA). Search for mimosa in the WAOL. using the scientific name Mimosa pigra.
Requirements for land owners/occupiers and other persons
Requirements for land owners/occupiers and other persons if this pest is found can be sourced through the declared plant requirements link.
Search > detect > report
Pest and Disease Information Service (PaDIS)
Report the presence of this organism before undertaking a control measure. Control methods for this declared plant can be found through the mimosa control link.