The shy ones from bean family- Mimosa

A large and diverse genus consisting of about four hundred and eighty species is found from Mimosa that is allied to Acasia. Mimosa is a genus of an annual and evergreen perennial plant, categorized as a shrub and small tree under the family of Fabaceae.

Unlike animals, plants are sessile, which are often regarded as immotile organisms. Plants do have slow movements that show apparent movement when the growth or movement are recorded using timelapse. The slow movements usually react to various environmental pressures such as the biological phenomenon called phototropism that is reacting to the light and other tropisms like aerotropism (towards oxygen), chemotropism (chemicals), electropism (electric field), gravitropism (gravity), hydrotropism (water), as well as hygrotropism (moisture or humidity). A plant, scientifically known as Mimosa pudica, is commonly known as humble plant, shy plant, sensitive plant, sleepy plant, action plant, shame plant, and touch-me-not can response to the external stimuli.

They are found in habitats varying from rainforest to dry savannah. Few are from America. Morphologically, plants under the genus of Mimosa have thorny stems that bear bipinnate leaves with the minutes. The inflorescence gave four to five-petalled flowers that have long stamens, which appear in a rounded head. The Mimosa from the florist point of view is the Australia acacia. They are frost-tender plants that prefer full sun as well as moderately fertile and well-drained soil. It needs frequent water during the growing period with a sparingly amount of water in the winter. It can be propagated through cuttings, which are a practical way to propagate them in summer. In addition, seedlings can be obtained from seed through germination. The seeds were formed in a legume or pod that is linear and oblong, which is one to one and a half centimeter and three millimeters broad. It was found that the margins of the pod are bristles-like appendages. Each pod contains two to four brown seeds.

It gave branched stems with a diffusely spreading canopy. This short-lived-evergreen subshrub also grows as an annual plant that is native to Brazil. It grows to a height and spread of around three feet that is one meter. It has a half-woody herb with the prickly stem as a physical plant defense mechanism. This sensitive plant grows on most well-drained soils, including scalped or eroded subsoil and even soil with low nutrient concentrations. Interestingly, small, fluffy, ball-shaped pink flowers are found in summer or all year round in tropical countries. The shy plant is shade tolerant, which does not compete with tall vegetation or grow under the forest canopies.

It is grown for its curiosity value because the fern-like leaves will close and droop when touched. The leaflets fold together in the early evening and reopen at sunrise. After some time, like within few minutes, the leaves will reopen. It is called bashful or sensitive because the leaflets fold together on touching, warming, and shaking. The phenomenon is called seismonastic movement due to a rapid change in turgor pressure and membrane permeability in the pulvini cells in the leaf regions with the rapid movement of calcium ions. At night, the leaves also fold and bend, which is termed nyctinasty movements. It is a reaction to the absence of light. Similar plant movements are consistently observed in specific plant organs in which some of the reactions are restricted to the reproductive organs. For example, contraction and shortening of the stigma in Mimulus luteus and change of the movement in the anther filaments in Centaurea.

The seismonastic movement is the leaflet movement throughout the bending movement that involves regulating movement and fragmentation of the actin cytoskeleton. Mimosa pudica is a thigmonastic plant that reacts in the bioelectrochemical responses to stressors such as electrostimulation, wound, wind, vibration, touch, drought, change of illumination, and hot or cold stimuli as one of the plant defense mechanisms for the protection from animals and some insects. It reacts to the stimulation by the closure of leaves and descent of the petiole. The action potentials in Mimosa pudica signalling mechanism share the same properties in the action potentials in animals. The mechanical movement involved in the shy plant is induced by the very high applied voltage, which is ranged from two hundred to four hundred volts between the soil and primary pulvinus. An osmotic pressure gradient is formed when the ions transportation has occurred between the upper and lower parts of the pulvini. Such a gradient created an osmotic flow of water via aquaporins that induced the falling of the petiole.

In some areas, this plant is becoming a noxious weed or invasive weed in some countries, especially in corns, soybeans, tomatoes, upland rice, cotton, bananas, sugarcane, coffee, oil palms, papayas, coconuts, as well as rubber in many tropical areas. This is because the roots of this species produce carbon disulfide, which made it selectively inhibits colonization of the rhizosphere by mycorrhizal and pathogenic fungi. This invasive species also can be found in croplands, orchards, pastures, mowed areas, roadsides, and areas disturbed by construction. It may grow as a single plant or in tangled thickets. It is particularly troublesome where hand pulling of weed is practiced due to the presence of the thorn on its stem.

Furthermore, this shy plant contains active compounds such as tannins, mimosine, and steroids in several parts of the plants. It has been used in traditional medicine. It has a bitter root with acrid, cooling, vulnerable, and alexipharmic properties often used in the treatments such as leprosy, dysentery, vaginal, uterine complaints, inflammations, burning sensation, asthma, leukoderma, and fatigue, as well as several diseases. Traditionally, the roots are usually cooked with water as a decoction to reduce toothache. It has been found that Mimosa pudica also has healing properties on the wound and prevents or slows down the bleeding process. Its herbal extract with medicinal properties can be used to cure skin diseases. In addition, the stem or bark can be involved in psychological treatment like mind relaxation, relieve depression, mental distress, irritability, severe palpitations, and amnesia. It is known as a mood enhancer, which improves the circulation of the blood. Despite its pharmacological properties as traditional medicine, it is not advisable for pregnant or nursing ladies.

Further readings:

Weintraub, M. (1952). Leaf movements in Mimosa pudica L. The New Phytologist50(3), 357-382.

Patil, H. S., & Vaijapurkar, S. (2007). Study of the geometry and folding pattern of leaves of Mimosa pudica. Journal of Bionic Engineering4(1), 19-23.

Volkov, A. G., Foster, J. C., Ashby, T. A., Walker, R. K., Johnson, J. A., & Markin, V. S. (2010). Mimosa pudica: electrical and mechanical stimulation of plant movements. Plant, cell & environment33(2), 163-173.

Azmi, L., Singh, M. K., & Akhtar, A. K. (2011). Pharmacological and biological overview on Mimosa pudica Linn. International journal of pharmacy & life sciences2(11).

Joseph, B., George, J., & Mohan, J. (2013). Pharmacology and traditional uses of Mimosa pudica. International journal of pharmaceutical sciences and drug research5(2), 41-44.

Patro, G., Bhattamisra, S. K., & Mohanty, B. K. (2016). Effects of Mimosa pudica L. leaves extract on anxiety, depression and memory. Avicenna journal of phytomedicine6(6), 696.