any plant of the genus Hemerocallis of the family Hemerocallidaceae, consisting of about 15 species of perennial herbs distributed from central Europe to eastern Asia. Members of the genus have long-stalked clusters of funnel- or bell-shaped flowers that range in colour from yellow to red and are each short-lived (hence “day” lily). Day lilies also have fleshy roots and narrow, sword-shaped leaves that are grouped at the base of the plant.