Agroforestree Database

Local names:
 English (pricky wood weed,mimosa,giant sensitive plant,catclaw mimosa,black mimosa), French (amourette riviére), Spanish (zorzon,zarza,dormilona), Thai (maiyaraap ton,mai yah raap yak)

Mimosa pigra is a prickly mimosoid shrub. Stems are branched, 2-6 m long, with dense growth. The stem has 5 ridges from which spines and bristles arise.

Leaves about 20 cm long and pinnate; 7-16 pairs pinnae, each pinna composed of 25-40 linear pinnules. Petioles and leaves spiny and hispid. The leaves are not as sensitive to physical stimulation as those of some other Mimosa spp.

Many globose inflorescences arise from the end of the stem and from leaf axils. Pale reddish-purple stamens conspicuous in the florets.

Pods compressed, 5-10 cm long, about 2 cm wide and densely hispid.

The generic name ‘mimosa’ is from the Greek meaning to imitate or mimic. This refers to some species of the genus that may appear to imitate animals because the sensitive leaflets move and fold up when touched.

Ecology

M. pigra is a legume of moist, open sites in the tropics, forming a monospecific stand and competing with sedgeland and grassland communities so that the ground flora under dense stands is sparse to non-existent. Its favoured habitat is around water and on floodplains. Since the late 1970s, the plant has become a serious weed of pastureland and national parks in northern Australia. M. pigra has several characteristics that enable it to do well in open disturbed sites: it grows quickly, it can withstand drought and floods, and the seeds float. It threatens biological diversity by replacing wetlands with an impenetrable thorny thicket. It is also detrimental to pastoralism, tourism and traditional use of land by Aboriginal people.
M. pigra presents a very different picture in its native range, where its natural habitat is mainly marginal areas of canals, rivers and lakes, and this gives some hope to researchers looking for biological controls. In Mexico, for example, it is a rather obscure weed.

Native range
Argentina, Bolivia, Brazil, Chile, Colombia, Ecuador, French Guiana, Guadeloupe, Guyana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru, Surinam, Uruguay, Venezuela

Tree management

Mature M. pigra is resistant to fire, the majority of plants regrowing from the base of stems. Young plants are more susceptible, but a large proportion also regrow. Plants that are 1st stressed with herbicides have a higher level of mortality than unstressed plants. The burn season is also important; there is higher mortality when plants are drought stressed than from burning soon after rain.

Mimosa infestations can expand very rapidly, so it is important to prevent the spread to new areas, as well as to control existing infestations. Current control methods are costly and require lengthy ongoing commitment.

Seed storage behaviour is orthodox under long-term storage. The oldest recorded collection is 4 years old.

M. pigra is a legume of moist, open sites in the tropics, forming a monospecific stand and competing with sedgeland and grassland communities so that the ground flora under dense stands is sparse to non-existent. Its favoured habitat is around water and on floodplains. Since the late 1970s, the plant has become a serious weed of pastureland and national parks in northern Australia. M. pigra has several characteristics that enable it to do well in open disturbed sites: it grows quickly, it can withstand drought and floods, and the seeds float. It threatens biological diversity by replacing wetlands with an impenetrable thorny thicket. It is also detrimental to pastoralism, tourism and traditional use of land by Aboriginal people.
M. pigra presents a very different picture in its native range, where its natural habitat is mainly marginal areas of canals, rivers and lakes, and this gives some hope to researchers looking for biological controls. In Mexico, for example, it is a rather obscure weed.

Mature seeds show only 2% germination under normal laboratory conditions. Seed dormancy is due to the impermeability of the seed coat to water when the mc drops below 10% of fresh weight. Immersing the seed in boiling water for 1-2 minutes breaks dormancy; the result is about 98% germination. M. pigra seeds also germinate profusely after burning.

Erosion control: M. pigra can be used on the steep banks of water reservoirs as an erosion-control measure.

Apiculture: According to reliable beekeepers in Thailand, M. pigra can serve as a pollen source for bees.

When groundwater levels start falling at the beginning of the dry season, the defoliated stems and branches are left and become dry. These dry materials are collected and utilized as firewood by the low-income people living in the vicinity of the reservoirs. The use of this material as firewood releases the wood harvesting pressure in the upstream area of the reservoir.

Tannin or dyestuff: The root yields 10% tannin.

Medicine: M. pigra is used in tropical Africa as a tonic and for diarrhoea, gonorrhoea and blood poisoning. In Tanzania, the powdered leaf is taken with water to relieve swelling. In Zambia, the root ash is sprinkled over leprous patches on the skin. The root is apparently aphrodisiac to some persons and calming to others. The seed is emetic and an expectorant and is used for tooth troubles. The leaf is said to contain mimosine; it is purgative and perhaps tonic.

Soil improver: It has been used as a green manure and cover crop in Thailand since the 1960s.

Pollution control: M. pigra grown at the damp water-inlet areas in reservoirs can remove debris from floodwater entering the reservoir.