sensitive plant

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A shrubby plant (Mimosa pudica) in the pea family, native to tropical America, having mauve flower heads and bipinnately compound leaves with leaflets that fold and droop when touched.
• noun Any of various similar plants, such as Chamaecrista nictitans.

from The Century Dictionary.

• noun The tropical and greenhouse plant Mimosa pudica; the humble-plant.
• noun Same as sensitive pea (which see, under pea).
• noun The narrow-leaved sensitive-brier, Leptoglottis angustata (Schrankia angustata of Torrey and Gray), found from Virginia to Florida aud west to Tennessee and Texas.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun semi-climbing prickly evergreen shrub of tropical America having compound leaves sensitive to light and touch
• noun prostrate or semi-erect subshrub of tropical America, and Australia; heavily armed with recurved thorns and having sensitive soft grey-green leaflets that fold and droop at night or when touched or cooled