Definition of sensitive briar in US English:

sensitive briar

noun

  • A herbaceous perennial leguminous plant, Mimosa nuttallii, native to the central United States, having prickly stems that trail along the ground, pink or purple flowers with conspicuous stamens that form a globelike cluster, and leaflets that fold together when touched.

Origin

Early 19th century; earliest use found in John Drayton (1766–1822).