Sensitive Briar

Sensitive Briar, Mimosa spp. (likely Mimosa nuttallii).

Sensitive briar is a common name given to a number of Mimosa spp. with leaves that respond to touch. Generally, these plants have puffed, pink fragrant flowers on a woody, thorned vine. Most are commonly seen during summer, but a few species appear during the fall. As a member of the legume family, Fabaceae, their fruits are flattened pods similar to its pea relatives. The characteristic movement of the leaflets of sensitive briar is known as thigmonastic movement. A structure called the pulvinus is located at the base of each leaflet which can control water pressure. When touched, that pressure is lost causing the leaflets to collapse. Thigmonastic movement is believed to be a deterrent to herbivores as the leaves become hard to reach and the prickles and thorns are exposed.