Mimosa pudica, commonly known as "sensitive plant," "sleeping grass" or "touch-me-not," 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.
Mimosa pudica is a member of the Mimosaceae family. Its name is derived from the Greek work for "mimic" and the Latin word for "bashful" or "shrinking." The species is native to South America and Central America, but is now a pantropical weed.
Features
Mimosa pudica has a thorny stem and pale green leaves resembling those of ferns. The leaves are bipinnately compound, with one or two pinnae pairs, and 10-26 leaflets per pinna. The leaves are known for closing in on themselves when touched or exposed to other stimuli such as fire and wind.
The prickly stem of the Mimosa pudica is slender and upright in a young plant and trails like a ground cover as the plant ages. The leaves grow in pairs on either side of three-inch stems branching off of the main stem.
Reproduction
Mimosa pudica seeds are spread by either water or their bristles, which stick to animal fur or human clothing. Mimosa pudica blooms in mid to late summer, producing fluffy pink flowers that take a spherical shape. Its flowers produce long seed pods, each with three to four light brown seeds and require either bees or the wind for pollination.
Energy Acquiring
Like many other legumes, the sensitive plant acquires energy from an association with nitrogen-fixing bacteria, which live within its root nodules. The plants make use of certain form of atmosphere nitrogen which converted by the bacteria, and then grow upon its aids.
Process of leaflet movement
The leaves of the Mimosa pudica have long fascinated people, because the leaflets fold together on touching, warming and shaking. This plant employs both nyctinastic and seismonastic movements. The first phenomenon is called seismonastic movement due to a rapid change in their internal (turgor) pressure and changes in membrane permeability in the pulvini cells in the leaf regions with rapid movement of calcium ions. It is the temporary movement of a plant in reaction to touch, warmth, or lack of water. This movement is accomplished by an electrical and chemical response in the plant. At night, the leaves also fold and bend, and reopen during the day, termed nyctonastic movements (reaction to absence of light).
l Function
The opening and closing of the plants' leaflets and the entire leaf are controlled by a fluid filled sac-like structures found at the base of the compound leaf and each leaflet. The swollen base of the leaf stalk is called ‘pulvinus’. When the plant is touched, electrical signals are flashed by the cells. The cells in the ‘pulvinus’ respond to this signal by flushing out potassium and water. With the massive loss of water, the pulvinus bends over and the leaflets fold.
How do the leaflet movement feature work to its advantage?
The ability to fold its leaves may benefit the sensitive plant in three ways. It has been observed that folded and drooped leaves are not attractive to herbivores, and are often passed by in favor of more normal appearing leaves to eat. Plus, the sensitive plant may also fold its leaves in an attempt to exchange less water and prevent to be too dry. The undersides of leaves are lined with tiny holes, called stomata, through which the plants breathe. Plants lose significant amounts of water while exchanging gas through the stomata, so the plant can conserve water by closing off as many stomata as possible. Finally, sensitive plants close their leaves when not exposed to the sun, which the drooped leaves would thus exchange less heat. In what is called a "nyctinastic response" the plant responds to dropping levels of sunlight by closing its leaves, keeping them safe through the night.
Threats:
The sensitive plant is threatened and suffering from pests such as red spider mite, thrips and mealy bugs.
Creative Ideas from the leaflet movement feature
l Safe Window
Based on the folding and bending feature of the sensitive plants, windows that are able to protect the house from theft or robbery can be developed by applying this leaflet movement function. Basically, the set or device which equipped with such function would not really appeared as plants’ leaves, but only takes advantage of Mimosa pudica’s smart and sensitive feature. Specifically, since the nyctinastic movement would cause drooped leaves during the night. The window would only implement the movement of seismonastic which would react to human’s touch. Once the thief intends to climb across the window and touches the screen, the set will automatically folding or bending like the sensitive plant and thus be able to catch the thief.
l Energy-saving and Thermostatic Greenhouse
One of the remarkable movements that enable the sensitive plant to fold its leaves is seismonastic movement which is the temporary movement of a plant in reaction to touch, warmth, or lack of water. According to the benefits mentioned above from this movement, folded and drooped leaves exchange less heat and water than fully expanded leaves in attempt to become too dry, hot or cold. This kind of adaptive feature could be used to create an energy-saving and thermostatic greenhouse for farmers and gardeners. The greenhouse could be covered with a fabric that functions like the sensitive plant. By controlling the temperature and moisture automatically like the sensitive plant, this kind of fabric (or other possible materials) would keep the greenhouse at a constant temperature and prevent the seedlings or flowers in the greenhouse from dryness and frostbite.
One of the remarkable movements that enable the sensitive plant to fold its leaves is seismonastic movement which is the temporary movement of a plant in reaction to touch, warmth, or lack of water. According to the benefits mentioned above from this movement, folded and drooped leaves exchange less heat and water than fully expanded leaves in attempt to become too dry, hot or cold. This kind of adaptive feature could be used to create an energy-saving and thermostatic greenhouse for farmers and gardeners. The greenhouse could be covered with a fabric that functions like the sensitive plant. By controlling the temperature and moisture automatically like the sensitive plant, this kind of fabric (or other possible materials) would keep the greenhouse at a constant temperature and prevent the seedlings or flowers in the greenhouse from dryness and frostbite.
References:
1. Barneby, R. (1991). Sensitivae censitae: a description of the genus Mimosa Linnaeus (Mimosaceae) in the New World. New York Botanical Garden, New York.
2. Weintraub, M. (1951). Leaf movements in Mimosa pudica L. New Phytol. 50: 357-382.
3. http://en.wikipedia.org/wiki/Mimosa_pudica
4. http://en.wikipedia.org/wiki/Thisgmonasty
5. http://www.mls.sophia.ac.jp/~kanzawa/research-e.html
6. http://www.hindu.com/thehindu/seta/2001/12/06/stories/2001120600130400.htm
