any of about 10 species constituting the genus Lolium (family Poaceae), which includes forage and lawn grasses of temperate Eurasia and the noxious weed known as darnel (L. temulentum). Ryegrasses are about 0.3 to 1 m (1 to 3 feet) tall and have tough, dark green leaves. The flower spikelets grow in the angles of a zigzag rachis (flower stem). Both perennial ryegrass (L. perenne) and Italian ryegrass (L. multiflorum) germinate early and are important constituents of pasture and lawn-seed mixtures.
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