in botany, a genus of the monoeia triandra clasps. The amentum of both male and female is roundish; and the calyx of both consists of three leaves; neither of them have any corolla; the stigma of the female is bifid; and the drupa is dry, and contains two seeds. There are two species, both natives of Britain, viz. the erectum, or great-bur-reed; and the natans, or least bur-reed.