THE plant, Mimosa pudica goes by many common names like: “sensitive plant,” “touch me not plant,” “sleepy head,” “I died, I Lived” “Shy plant” “false death” humble plant.

Few can resist touching the compound leaves of Mimosa pudica and watching them fold up in response. The plant is popular in cultivation around the world, it is enjoyed by many for its curiosity value. Its touch-sensitive leaves create interest among adults and children alike, helping to inspire interest in plant life generally.

Mimosa pudica (from latin: “Pudica” shy, bashful or shrinking to contact). The generic name “Mimosa” is derived from Greek mimos (meaning mimic) in reference to the fact that the leaves move in response to something moving against them.

Mimosa is a genus of about 400 species of herbs and shrubs, in the sub family Mimosoideae of the legume family Fabaceae. There are two species in the genus that are notable. Mimosa pudica, which is widely cultivated for its curiosity value, both as a house plant in temperate areas and outdoors in the tropics. The other species in the genus is Mimosa tenuiflora which is best known for its use in shamanic ayahuasca brews due to the psychedelic drug, dimethyltryptamine, found in its root bark.

Description

Members of this genus are among the few plants capable of rapid movement; examples outside of Mimosa include the “telegraph plant” and the “venus fly trap.”

The leaves of the plant close quickly when touched. Some Mimosa raise their leaves in day, time and lower them at night. Mimosa pudica is well known for its rapid movement. Like a number of other plant species, it undergoes changes in leave orientation termed “sleep” or nyctinastic movement. The foliage closes during darkness and reopens in light.

The leaves also close under various stimuli, such as touching, warming, blowing, or shaking. These type 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, the deferential turgidity between different regions of cells result 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.

The stimulus can also be transmitted to neighbouring leaves. It is not known exactly why Mimosa pudica evolved this trait, but many scientists think that the plant uses its ability to shrink as a defense from predators. Animals may be afraid of a fast moving plant and would rather eat a less active one. Another possible explanation is that the sudden movement dislodges harmful insects. It may also be response against leaching loss of nutrients, or desiccation.

It is not the only member of the legume plant family (leguminosae) to move in response to stimuli, more species of mimosa show sensitivity to touch. Other legumes, for example some members of the genera are Neptunia, Acacia, Albizia, and Samanea, respond to a lesser degree by showing sleep movement (nyctinasty) in their natural habitats.

This involves the closing of the leaves a few hours before dusk, and re opening of the leaves a few hours before dawn. It is thought that, these sleep movements aid water conservation as well as defence against herbivory.

Mimosa pudica is native to South America and Central America, but is now pantropical in distribution.

The stem is erect in young plants, but becomes creeping or trailing with age. It can hang very low and become floppy. The stem is slender, branching, and sparsely to densely prickly, growing to a length of 1.5m (5ft). The leaves of 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 flowerheads arise from the leaf axils with more and more flowers as the plant gets older. The globose to ovoid heads are 8-10mm in diameter (excluding the stamens). On close examination, it is seen that the floret petals are red in their upper part and the filaments are pink to lavender. The fruits consists of clusters of 2-8 pods from 1-2 cm long each, these prickly on the margins. The pods break into 2-5 segments and contain pale brown seeds some 2.5mm long.

The flowers are pollinated by the wind and insects. The seeds have hard coats which restrict germination.

Ecology

Mimosa pudica plant grows on most well-drained soils, even scalped or eroded subsoils and soils with low nutrient concentrations. It requires disturbed soils to establish itself. Repeated burning may encourage its spread in pastures. It is shade-intolerant and does not compete with tall vegetation or grow under forest canopies.

Agricultural Impact

The species can be a troublesome weed to tropical crops, particularly when fields are hand-cultivated as it has prickles along its stems. Crops it tends to affect are corn, coconuts, tomatoes, coffee, bananas, soybeans, papaya, upland rice, sugar cane, rubber.

It can be controlled by a number of commercial broad leaf herbicides: on the other hand, it is tolerated or valued as a forage plant in pastures.

Mimosa pudica can form root nodules that are habitable by nitrogen-fixing bacteria 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.

Propagation is generally by seed

The seed is scarified (scratched) and soaked in water overnight. The seed germinates easily and it is possible to see the beginning of root growth by the next day. legumes).

Medicinal Uses

Mimosa has been used widely in traditional medicine. Pulped leaves are used in India on glandular swellings and in the Republic of the Congo (Congo Brazaville) the entire plant is pulped and rubbed onto people suffering pains in the body sides and kidney. In Senegal, the leaves are used for lumbago and nephritis. All parts of the plant have been used to combat grandular tumours and uterine cancer.

In India, leaf-sap is applied for sinus disorders, and rubbed onto sores and piles.

Chemical Constituents

Mimosa Pudica contains the toxic alkaloid, mimosine, which has been found to also have antiproliferative and apoptotic effects. The extracts of Mimosa pudica immobilize the filariform larvae of Strongyloides stercoralis in less than one hour. Aquevus extracs of the roots of the plant have shown significant neutralizing effects in the lethality of the venom of the monocled cobra (Naja Kaouthia). It appears to inhibit the myotoxicity and enzyme activity of cobra venom. Extracts of the plant have been shown in scientific trials to be a moderate diuretic, antidepressant, promote regeneration of nerves, reduce menorrhagia, and the roots extracts to be a strong emetic.

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