Mimosa pudica L or touch-me-not plant has an unique phenomenon in its ability to close the leaves even for the slightest touch stimuli. Touch-me-not plant is also called by the names humble plant, shameful plant, sensitive plant etc. Mimosa pudica belongs to legume family. Mimosa is a short, prickly, perennial herb with branches growing close to ground. The generic name Mimosa is derived from the Greek in which "mimos" means to "mimic". Latin word "pudica", means "bashful or shrinking to contact".
Nyctinastic & seismonastic movement
During night leaves of Mimosa close up and reopen in the morning. This is called as nyctinastic movement or sleep movement. Leaves of Mimosa fold inward and droop for the stimuli such as touching, warming, blowing, or shaking. This type of movement is called as seismonastic movement.
Turgor pressure is exerted by the water onto cell wall, vacuoles and other cell contents of the plant. The stimulus such as touch triggers the release of chemicals including potassium ions from certain areas of the stem. As a result water from the vacuoles of the cell comes out and turgor pressure is dropped. This result in collapsing of cells and leaflets are closed. This movement to touch stimulus appears to be the defense mechanism against herbivores. It’s interesting to note that Indian scientist Jagadish Chandra Bose observed this response in plant and demonstrated the fact that plants also can feel pain.