sandbur or bur grass, any species of the genus Cenchrus of the family Gramineae (grass family), sandy-soil plants of tropical and temperate regions. At maturity the sharp spines and burlike seeds make the plant a troublesome weed, especially to sheepgrowers. The name sandbur is sometimes used for the buffalo bur and the horse nettle of the family Solanaceae (nightshade family). The family Gramineae is classified in the division Magnoliophyta, class Liliopsida, order Cyperales. The Solanaceae is in the class Magnoliopsida, order Polemoniales.