mimosa, any tree, shrub, or herb of the genus Mimosa of the family Leguminosae (pulse family), chiefly tropical plants. They usually have feathery foliage and rounded clusters of fragrant pinkish flowers atop the branches. Mimosas are used for ornamental purposes in warm regions. The yellow-flowered plants sold as mimosa by florists are usually of the related genus Acacia (see acacia). Most widely known of the mimosas is the sensitive plant (M. pudica), considered a weed in the American tropics but cultivated as a greenhouse annual elsewhere because its leaves fold up and collapse under stimulus (e.g., touch, darkness, or drought) until the whole plant may assume temporarily a thoroughly wilted appearance. It is now naturalized in many warm regions and grows wild in the Gulf states. The name sensitive plant is also applied to other plants of this family that show similar movements. Mimosa is classified in the division Magnoliophyta, class Magnoliopsida, order Rosales, family Leguminosae.

Mimosa or Beta Crucis, bright star in the constellation Crux (Southern Cross); 1992 position R.A. 12^h47.3^m, Dec. -59°39'. It is sometimes called Becrux, from its Bayer name, analogous to Acrux (Alpha Crucis) and Gacrux (Gamma Crucis). A bluish-white giant of spectral class B0 III, its apparent magnitude of 1.28 makes it one of the 20 brightest stars in the sky. Mimosa's distance is c.500 light-years.

Any member of the more than 450 species that make up the genus Mimosa in the family Mimosaceae, native to tropical and subtropical areas throughout both hemispheres. Most are herbaceous plants or undershrubs; some are woody climbers; a few are small trees. They are often prickly. Mimosas are widely cultivated for the beauty of their foliage and for their interesting response to light and mechanical stimuli: the leaves of some species droop in response to darkness and close up their leaflets when touched. The name comes from this “mimicking” of animal sensibility. The roots of some species are poisonous; others contain skin irritants. Many acacias are commonly but incorrectly called mimosas. Seealso sensitive plant.

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