EIACP PC Hub: Kerala
State of Environment and Related Issues

  Mimosa pudica (Thotta vadi, Sensitive Plant and the touch-me-not)       

     The plant is a creeping annual or perennial herb often grown for its curiosity value, the compound leaves fold inward and droop when touched or shaken, re-opening minutes later. The species is native to South America and Central America, but is now a pantropical weed.

Description: The stem is erect in young plants, but becomes creeping or trailing with age. The stem is slender, branching, and sparsely to densely prickly, growing to a length of 1.5 m (5 ft). The leaves of the Mimosa pudica are compound leaves. The leaves are bipinnately compound, with one or two pinnae pairs, and 10-26 leaflets per pinna. The petioles are also prickly. Pedunculate (stalked) pale pink or purple flower heads arise from the leaf axils. The globose to ovoid heads are 8–10 mm in diameter (excluding the stamens).

Distribution: Mimosa pudica is native to South America and Central America. It has been introduced to many other regions and is regarded as an invasive species in Tanzania, South Asia and South East Asia and many Pacific Islands. It is regarded as invasive in parts of Australia and is a declared weed in the Northern Territory and Western Australia although not naturalized there.

Plant movement: Mimosa pudica is well known for its rapid plant movement. Like a number of other plant species, it undergoes changes in leaf orientation termed "sleep" or nyctinastic movement. The foliage closes during darkness and reopens in light. The leaves also close under various other stimuli, such as touching, warming, blowing, or shaking. These types of movements have been termed seismonastic movements. The movement occurs when specific regions of cells lose turgor pressure, which is the force that is applied onto the cell wall by water within the cell vacuoles and other cell contents. When the plant is disturbed, specific regions on the stems are stimulated to release chemicals including potassium ions which force water out of the cell vacuoles and the water diffuses out of the cells, producing a loss of cell pressure and cell collapse; this differential turgidity between different regions of cells results in the closing of the leaflets and the collapse of the leaf petiole. This characteristic is quite common within the Mimosoideae subfamily of the legume family, Fabaceae.

Medicinal Use: In contemporary medicine, Mimosa pudica is being investigated for its potential to yield novel chemotherapeutic compounds. It contains an alkaloid called mimosine, which has been found to have potent antiproliferative and apoptotic effects. Aqueous extracts of the roots of the plant have shown significant neutralizing effects in the lethality of the venom of the monocled cobra. It appears to inhibit the myotoxicity and enzyme activity of cobra venom.

            In Ayurveda, the plant is described as a plant which folds itself when touched and spreads its leaves once again after a while. It is said to have a bitter and astringent taste. It is used for diarrhea (athisaara), Amoebic dysentery (raktaatisaara), gynecological disorders, skin diseases, bronchitis, general weakness and impotence. Most commonly used is the root, but leaves, flowers, bark, and fruit can also be implemented.

Agricultural Impacts: The species can be a troublesome weed in tropical crops, particularly when fields are hand cultivated. Crops it tends to affect are corn, coconuts, tomatoes, cotton, coffee, bananas, soybeans, papaya, and sugar cane. Mimosa pudica can form root nodules that are inhabitable by nitrogen fixing bacteria. The bacteria are able to convert atmospheric nitrogen, which plants can not use, into a form that plants can use. This trait is common among plants in the Fabaceae family.