bur

(burr) A type of *pseudocarp in which the fruit is surrounded by a persistent barbed involucre as, for example, in burdocks (Arctium) and cocklebur (Xanthium). Often the term refers to any barbed fruits, e.g. those of cleavers (Galium aparine) and enchanter's nightshade (Circaea lutetiana) both of which have hooks borne directly on the pericarp. Burs cling to passing animals and are thus widely dispersed.