All of its names stem from the plant's unusual response to stimulus: when it is touched, its leaves fold up and its branches droop, leaving it looking dead or sick in a matter of seconds. Give it 10–20 minutes without further contact to recover, though, and it perks back up, good as new. This is a type of rapid plant movement called thigmonasty or seismonasty or haptonasty and comes as a direct reaction to physical contact. When a stimulus comes into contact with certain areas of the plant's stem, those areas release chemicals that cause water, calcium, potassium, and chlorine in the stem to shift, an action known as osmosis, which, in turn, causes the cell wall to lose its rigidity and the plant to droop.
Scientists aren't exactly sure why the Sensitive Plant has developed this reaction, but theories lean toward it being a protective feature against herbivores who might be inclined to eat it or climb on it. Other plants that exhibit thigmonasty include the Venus Fly Trap, which closes in around a source of touch that may be food for it, and certain thistles, whose anthers shrink and then rebound, coating a source of contact in pollen as a form of propogation.
Considered a roadside weed in its native Central and South America, the Mimosa pudica has compound leaves that bear a passing resemblance to those of a fern. It bears clusters of prickly seed pods and flowers that are pink or lilac and globular, similar to a dandelion puff-ball.
The Sensitive Plant is used in Ayurveda medicine, a type of traditional medicine that originated in India, to relieve symptoms of illnesses and discomforts as wide-ranging as diarrhea, hemorrhoids, toothache, swollen glands, lumbago, sinus disorders, and snake bites. It is not widely used within Western medicine, but is being researched for that purpose, although there are concerns about the plant's toxicity. In addition to its medicinal purposes, it also is used as pastureland for cattle and to prevent soil erosion, as well as being a popular houseplant.
Want to learn more about interesting plants? Check out the Plant Hunter tool from the New York Botanical Garden and learn about dozens of different plants from around the globe. Younger students can engage in lessons on how seeds grow, the various parts of a plant, and take part in a hands-on gardening project. Older students can learn how plants reproduce, plan a wildflower garden, and listen to a story about other ways plants respond to their environment.
