Name:
Mimosa (Mimosa Pigra)
Description:
Mimosa (Mimosa pigra) is a shrub to 5 or 6 m tall, with scattered 5-12 mm long thorns along the stems and branches. Its touch-sensitive leaves are about 12-22 cm long, and consist of many fine leaflets (up to 45 pairs). Its round flower heads (about 10-20 mm in diameter) are composed of about 100 individual pink or mauve flowers. Seed pods are clustered, with 10-20 produced in each flower head. The pods are flat, linear, 30-120 mm long, 7-14 mm wide and densely hairy with rustycoloured bristles. They break into segments when mature, each segment containing an oblong shaped brown or olive-green seed (4-6 mm long, 2-3 mm wide). There can be anything from 14 to 26 seeds per pod.
For further information and assistance with identification of Mimosa contact the herbarium in your state or territory.
Distribution:
In Australia Mimosa is mostly confined to the Northern Territory, although it has been recorded in northern Western Australia near the NT border (Navie 2004). A small infestation of plants discovered in 2001 near Proserpine in Queensland has been removed, and there is active monitoring of the area and control of new emerging seedlings.
Following its introduction to Darwin, Mimosa was not particularly invasive and the populations were generally stable until the 1950s. However, about that time it had spread enough to reach its favoured habitat - open floodplains - and began to spread rapidly. Concerted efforts to eradicate the weed were carried out in the 1960s and early 1970s, however monocultures of this plant now infest most major river systems in the Top End, from the Victoria River in the west to the Phelp River in south-eastern Arnhem Land and the Arafura Swamp to the north-east.
Habit:
Shrub
Key points:
- Preventing the spread of Mimosa (Mimosa pigra) is essential in protecting northern wetlands; in the Top End more than 80 000 hectares of native vegetation on wetlands has been replaced by Mimosa.
- Once established, Mimosa is very difficult to control.
- Prevent Mimosa spread by using effective quarantine, hygiene and monitoring, and by controlling feral animals.
- Control Mimosa in small patches before it seeds by hand pulling, bulldozing or spraying herbicides.
- Larger infestations should be sprayed from the air. Follow-up will be required.
- Biological control agents help to control Mimosa in the long term.
How it spreads:
Mimosa produces copious amounts of seed. A typical annual production of perhaps 9 000 seeds and as many as 220 000 has been recorded for a particularly productive individual. Seeds are readily dispersed by humans, animals and water. At maturity, pods disintegrate into one-seeded segments, with the hairs on the surface of the pod ensuring that they are readily attached to fur and clothing. If consumed by animals, seed also passes unharmed through the digestive tract. Seed, in mud, can also be dispersed by vehicles. It is believed that sand contaminated with seeds was removed from the Adelaide River in the 1950s and used around the Top End in commercial building operations, leading to further spread of the species. However, on floodplains the most important dispersal method is simply water, which carries segments downstream
Where it grows:
Mimosa favours humid and sub-humid tropical regions, growing on a variety of soils in moist sites such as riverbanks, coastal plains and floodplains.
Flower colour:
Pink
Distribution map:
Impacts:
Mimosa is a Weed of National Significance. It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts.
Mimosa forms dense stands that replace all native vegetation on the ecologically and economically valuable wetlands of the Top End of northern Australia. Mimosa invasion threatens the production, cultural and conservation values of wetlands, and reduces the scope for exploitation of resources by land users. Pastoralists are affected because the inedible and thorny Mimosa smothers and replaces grasslands, blocks access to stock watering points and hinders mustering. Additionally, the harvesting of bush foods by indigenous people is hampered by Mimosa.
In environmental terms, nationally and internationally significant wetlands are threatened by Mimosa, which reduces the biodiversity of plant and animal life on the floodplains by out-competing native plants and reducing available habitat for native animals. Although currently limited in distribution, if left unchecked Mimosa has the potential to dominate wetlands across the whole of northern Australia.
Origin:
Mimosa is native to tropical America and now widespread throughout tropical regions of the world.
