Either of two plants in the pea family (see legume) that close up their leaves and droop when touched. This unusually quick response is due to rapid water release from specialized cells at the bases of leaftsalks. The more common plant is Mimosa pudica (see mimosa). Spiny and shrubby, with fernlike leaves and small, globular, mauve flower puffs, it grows about 1 ft (30 cm) high as a widespread tropical weed and a greenhouse curiosity. Wild sensitive plant (Cassia nictitans) is less sensitive to touch; a larger plant, 20 in. (50 cm) high, it is native to the eastern U.S. and the West Indies.

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