Mimosa strigillosa

sensitive plant, powderpuff

The sensitive plant is one of the few plants you can easily observe moving in real time. Leaflets will close up in response to touch, presumably as a defense against herbivores who may be either physically thrown off the leaf (tiny herbivores) or mentally thrown off and choose to browse elsewhere. Here's a great little video of the leaves of Brazilian sensitive plant (Mimosa pudica) closing in response to touch and heat, as well as time-lapse footage of them opening back up again:

The movement apparently doesn’t throw off cattle, as they enjoy browsing the nutritious groundcover, which contributes to quality meat and milk production. Too much of this good thing, however, is toxic for the cows, so moderation is required. Instead of being used for grazing, the plant may be used as a green manure since it is so rich in nutrients, especially nitrogen. Since it is such a rapidly spreading plant with taproots, it has been used for erosion control and as a replacement ground cover for lawns in Florida.

The leaves move when touch causes the release of ions near cells at the bases of the leaflets, which in turn causes water to move out of the cells into the surrounding solution. Since the leaflets rely on strong water pressure in these cells to stay fully open, they begin to close as the water leaves the cells.

Extracts made from the roots of Brazilian sensitive plant are able to significantly neutralize the toxicity of the venom of monocled cobras and also act as an antibacterial. The plant has many other uses throughout the world in traditional medicine, especially in Africa and India, where the plant is used to treat sleeplessness. Notably, the plant has been used to treat uterine cancer and glandular tumors. Western medicine currently doesn’t use the plant, but its potential is being investigated.