pampas grass, any species of the genus Cortaderia, tall South American plants of the family Gramineae (grass family) cultivated in warm climates for ornament. The common pampas grass (C. argentea or selloana) is a perennial with a cluster of long narrow drooping leaf blades. The male and female flowers are borne on separate plants; the ones which bear the female flowers have large, silvery, plumelike panicles which are sold for decorative purposes. Pampas grass is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.