Description:
Catclaw mimosa (Mimosa pellita) Weed.
When mature, Mimosa pigra is an erect, much branched prickly shrub reaching a height of 3m to 6m. Stems are greenish at first but become woody, are up to 3m long, and have randomly scattered, slightly recurved prickles 0.5cm tocm long. Leaves are bright green, 20cm to 25cm long and bipinnate, consisting of about 15 pairs of opposite primary segments 5cm long with sessile, narrowly lanceolate leaflets that fold together when touched or injured and at night. The flowers are pink or mauve, small, regular and grouped into globular heads 1cm to 2cm in diameter. The heads are borne on stalks 2cm to 3cm long, with two in each leaf axil, while the corolla has four lobes with eight pink stamens. The fruit is a thick hairy, 20-25 seeded, flattened pod borne in groups in the leaf axils, each 6.5cm to 7.5cm long and 0.7cm to 1cm wide. The fruit turns brown when mature, breaking into one-seeded segments. The seeds are brown or olive green, oblong, flattened, 4mm to 6mm long, and 2mm wide.
Occurs in:
Agricultural areas, coastland, natural forests, planted forests, range/grasslands, riparian zones, ruderal/disturbed, scrub/shrublands, urban areas, water courses, wetlands.
Habitat description:
Mimosa favours a wet-dry tropical climate and grows in open, moist sites such as floodplains, coastal plains and river banks. For example, in the
Catclaw mimosa (Mimosa pellita) Distribution in North America shown in green.
Mekong Delta, Vietnam, where it is a serious weed annual rainfall levels may reach up to 2200cm. It may not be a major problem in regions with an annual rainfall of less than 75mm or greater than 2250mm. In both Australia and Vietnam it prefers to invade seasonally inundated grassland.
It is more likely to colonise and eventually cause problems in disturbed areas. This is due to the ability of Mimosa seeds to establish rapidly on bare soils, which lack competitive pressures imposed by other seedlings. It is common along the edges of reservoirs, canals, river banks and roadside ditches, and in agricultural lands and overgrazed floodplains. In Vietnam it is typically found along the edge of both natural and manmade water bodies and along roadsides. In Australia it is known to spread very rapidly within overgrazed rangelands, and within Costa Rica (part of its native range) it is common in overgrazed areas.
Mimosa does not appear to grow preferentially in any soil type, but is found most commonly in soils ranging from black cracking clays to sandy clays to coarse siliceous river sand. Seed production and plant life expectancy are greater on black cracking clays than on the lighter clays and silty loams.
General impacts:
River floodplains and swamp forests in northern Australia are threatened by dense thickets of Mimosa pigra. The weed supports fewer numbers of birds and lizards, less herbaceous plants and fewer tree seedlings. It prevents traditional food gathering by Aborigines on otherwise resource rich wetlands.
M. pigra has the potential to harm a wide number and variety of different types of primary production. If large infestations occur over farmland, mimosa may threaten the health of pastoral industries by reducing the area of grazing land and the carrying capacity of the land. Furthermore, if livestock are reliant on natural water sources for drinking, their access to water may be blocked. As a result, meat production and income may be reduced.
M. pigra may reduce water flow and increase silt levels, as it commonly colonises water course edges. This may threaten the sustainability of
Close up of the Catclaw mimosa (Mimosa pellita) Weed.
reservoirs and canals and any livelihoods reliant on them. For example, the weed negatively impacts rice cultivation in Thailand by blocking irrigation inlets (as well as encouraging increases in the numbers of rats and crabs, which damage crops).
M. pigra may interference with the cultivation of other economically-important plants. For example, M. pigra is able to compete with the young palm trees in immature oil palm plantations. This may cause a decrease in the production of palm oil.
Common along roadsides, mimosa may also increase the costs of maintaining power poles and cables used for electricity transmission. It may also decrease driver visibility, increasing the potential for traffic accidents.
Geographical range:
Native range: Mimosa pigra is native to tropical America where it occurs in a wide belt extending from Mexico through Central America to northern Argentina.
Known introduced range: It is a serious introduced weed in Africa, Asia, some Pacific islands, and in the Northern Territory, Australia.
Management information:
Preventative measures: Preventative weed control is the most cost efficient form of weed management. Comprehensive surveys should ensure isolated infestations are identified and targeted before they expand to uncontrollable levels. Educating the community is also an important tool. Restricting the movement of vehicles, stock, stock feed, soil and sand from infested areas is important to prevent the spread of mimosa seeds.
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