bent grass, any species of the genus Agrostis of the family Gramineae (grass family), chiefly slender, delicate plants native to cool climates. Many are used for forage or lawns. Important species naturalized from Europe include the creeping bent ( A. palustris ), a lawn and putting-green grass; colonial bent ( A. tenuis ), frequently used in lawn mixtures; and especially, redtop ( A. alba ), called also fiorin and herd's-grass. Redtop, a perennial with reddish panicles, is much used (often mixed with clover) for pasture and hay in NE America; it is also effective in erosion control. The cloud grass ( A. nebulosa ), native to Spain, is cultivated for use as an everlasting. Bent grass is classified in the division Magnoliophyta, class Liliopsida, order Cyperales, family Gramineae.