Eryngium yuccifolium (Button snake-root, Rattlesnake Master) is a common herbaceous perennial plant, native to the tallgrass prairies of central and eastern North America, from Minnesota east to Ohio and south to Texas and Florida. In the Chicago Region this species has a coefficient of conservatism of 9. It grows to 1.8 m tall, with linear leaves 15-100 cm long but only 1-3 cm broad, with bristly or spiny margins and a sharp tip. The flowers are produced in dense apical umbels 1-3 cm diameter, each flower greenish-white or bluish-white, 3-4 mm diameter. When this plant flowers, pollen matures before stigmas become receptive to maximize outcrossing. Rattlesnake master has unusually high seed set (close to 90%).