Sensitive plant (Mimosa pudica)
Few plants can equal Mimosa pudica in its power to move. I decided this plant’s fascinating ability to change the position of its leaflets under specific stimuli fits in perfectly with this project. It is most commonly called the sensitive plant, but is also referred to as shameplant, humble plant, sleeping grass, and ‘touch-me-not.’ The mimosa name comes from a Greek word meaning mimic, while pudica is Latin for bashful or shrinking. The scientists who named it thought that this plant’s movements imitated movements made by an animal.
The sensitive plant is actually a perennial. The shrubby plant will grow to roughly 18 inches with hairy stems. Each leafstalk is divided into four sprays. Each spray has multiple leaflets on each side, which gives it an appearance similar to a fern. The plant flowers from mid-spring to early autumn. Two flower buds are produced where the leafstalks join the main stem. Each flower is really a small cluster of flowers that resembles a pale, lilac pink color. The buds open from bottom to top, and one flower matures before the other. Each flower has four stamens that bear pollen sacs. At the bottom of the pistil, there is an ovary containing ovules. The pollen from the stamens is transferred to the pistil by insects. After pollination, the flowers bend downward. The fruits become pods that look like pods of the green pea. As the pods dry out, the seeds pop out of the pod with the pod cover still around it. When a seed germinates, it leaves both the pod and seed covers behind. Despite its perennial nature, the sensitive plant is most often cultivated as an annual in gardens. This is because it is difficult for it to last through the winter when not in its preferred tropical paradise. It also tends to turn yellowish as it ages.
Mimosa pudica is well known for its remarkable capability of rapid movement. When the leaflets are touched, they fold together almost instantly and the leafstalk droops. These movements, called thigmonastic movements, also occur when the plant is shaken, heated, rapidly cooled, and subjected to a lack of water. The speed of the response depends on the magnitude of the stimulus. Hitting the leaf firmly or supplying an intense heat source will cause the leaf to close rapidly. A gentle touch or a more modest heat source applied to leaflets will result in a slower response. If the stimulus is strong enough, it will create a domino effect causing all the leafstalks to droop and close their leaflets. The plant recovers between 15 minutes to a couple hours later. The amount of time depends whether the stimulus is heat or touch, what part of the plant is stimulated, ad how strong the stimulus is. After applying heat underneath the leafstalk, it typically takes at least an hour to recover. The sensitive plant even has a “bedtime!” At night, the leaves will also fold together and droop in movements known as nyctonastic movements. They stay “asleep” until sunrise the following morning.
It wasn’t until the 19th century that the movements were discovered to result from a rapid loss of pressure. At the base of each leaflet on the spray, there is a swelling called a pulvinus. These swellings also occur where the spray of leaflets joins the leafstalk. The pulvinus cells are swollen with liquid. When the plant is touched or when heat is applied, the liquid in the lower half of the pulvinus suddenly leaves these cells and fills the empty spaces surrounding the cells. When cells lose water, they collapse. This causes the leafstalk to bend down toward the collapsed cells. In the leaflets, however, the upper sides of the pulvini shrink so the leaflets close upward. How the cells in the pulvinus lose their internal, turgor, pressure to cause leaf movement is still unknown. Despite this, there are still reasons for it to take happen. Folded and drooped leaves are not attractive to herbivores, and often passed by for more appealing leaves to eat. Also, leaves in this state exchange less heat and water than fully expanded leaves. This might have some survival value when the plant is under environmental stress.
Mimosa pudica before stimulus Mimosa pudica response to stimulus
(c)Barry A. Rice/The Nature Conservancy 2005
There are also uses for Mimosa pudica in medicine. The seeds and other parts of M. pudica contain mimosine, an amino acid that is known to cause hair loss and depressed growth in mammals. Only an abnormally large dose would cause such problems in humans. Extracts of the plant have been shown in scientific trials to be a moderate diuretic, promote regeneration of nerves, and reduce menorrhagia. Antidepressant activity has been demonstrated in humans. Due to the mimosine, root extracts are reported to be a strong emetic, which means it causes vomitting. Although the plant is used in herbal medicine, especially the Indian Healthcare System , it is not yet used in mainstream medicine. Pharmaceutical companies are still researching its properties and uses.
Habitats and and distribution of Mimosa pudica
Data provider: New York Botanical Garden. Dataset - Vascular plant type specimens. Catologue #251284
Though Mimosa pudica is native to Brazil, it is now considered pantropical and naturalized throughout the tropics of Central and South America, Africa, and Asia. According to the World Wildlife Category, tropical and subtropical grasslands, savannas, and shrublands are the habitats in which the sensitive plant is found.
As a member of the pea family, Leguminosae, it has the ability to fix nitrogen from the air. This advantage makes it adaptable to most soil types, even those of low nutrient concentrations. It is commonly found in croplands, orchards, pastures, mowed areas, roadsides, moist waste ground, open plantations, and densely weeded areas. Primarily, Mimosa is more common in soils of poor nutrient quality because it is out-competed in richer nutrient soils. It grows from near sea level up to 1,300 m in elevation and usually in areas with annual
precipitations from about 1000 to over 2000 mm.The sensitive plant is shade intolerant and does not compete with tall vegetation or grow under forest canopies. It may grow as either a single plant or in tangled thickets. The species’ roots produce carbon disulfide, which selectively inhibits colonization of the rhizosphere by mycorrhizal and pathogenic fungi (similar to what we discussed in class).
Since this plant seems to grow in a variety of tropical regions, it has unfortunately become a problem in some of them. Mimosa pudica forms a dense ground cover, preventing reproduction of other species. This means the sensitive plant has become invasive in a few different tropical areas. It has become a serious weed in fields of corn, soybeans, tomatoes, upland rice, cotton, bananas, sugarcane, coffee, oil palms, papayas, coconuts, and rubber. It is also troublesome where hand pulling of weeds occurs, as its thorny stems can cause painful wounds. On the other hand, it is tolerated and even valued as a forage plant in pastures. In fact, sheep grazing is reported to control M. pudica in pastures and plantations. Though this plant prefers a most soil and surrounding, thickets of Mimosa may become a fire hazard when too dry.
As you can see from the distribution map above, the sensitive plant occurs most in Central and South America. This ecoregion contains an amazing amount of biodiversity. More than 10,000 species of vascular plants are found. There are also several hundred species of mammals, birds, reptiles, and amphibians. Much more effort is needed to preserve one of the biologically richest savanna regions in the world, since very little of this ecoregion is protected and agriculture development continues to destroy habitats.
Bibliography of References
Selsam, Millicent E., and Jerome Wexler. Mimosa, the Sensitive Plant. New York, N.Y. 10016: Will Morrow and Company, Inc., 1978.
Mimosa pudica. Plants in Motion. 25 Mar. 2003. 17 Feb. 2008 <http://plantsinmotion.bio.indiana.edu/plantmotion/movements/nastic/mimosa/mimosa.html>.
United States Department of Agriculture. Natural Resources Conservation Service. 24 May 2007. 17 Feb. 2008 <http://www.plants.usda.gov/java/profile?symbol=MIPU8>.
Common Sensitive Plant. 5 Sep. 2007. 17 Feb. 2008 <http://www.nrw.qld.gov.au/factsheets/pdf/pest/pp38.pdf>.
Picture Souces
-
-
- Distribution map of Mimosa pudica - http://data.gbif.org/species/13641141
Comments (0)
You don't have permission to comment on this page.