Upwind movement of achenes of Centaurea eriophora L. on the ground

The lightly compressed achenes of Centaurea eriophora L. bear a pappus composed of stiff bristles at their apex and have an elaiosome appendage at their base. The pappus is ineffective in keeping the achene wind-borne but does serve to regulate the movement of the achene on the ground in response to wind. In wind the achene swivels like a weather vane with the base of the achene pointing into the wind. In weak wind the pappus bristles prevent the achene from blowing away. In stronger wind the bristles move due to their flattened, flexible, hinge-like bases and act like ratchets against the substratum, thus enabling the achene to move upwind. In either case achenes remain in groups. Ants are attracted to the elaiosome and disperse the achenes. Wind-induced movement was explored by testing achenes on various substrata in a wind tunnel at free-stream speeds between 2 and 7 m s^-1.