A plant (Humulus lupulus) belonging to the family Cannabaceae, also including nettles and hemp. The plant is a rough-stemmed, tall-twining dioecious perennial herb. It is propagated by cuttings of underground stems. The male flowers are borne on loose stalks. The anthers burst to produce large quantities of pollen, which is wind-borne. The female flowers occur in a cluster consisting of a compressed central axis that holds many flowers. As the clusters mature, the central axis elongates and papery leaves replace each flower, growing into a conelike structure, which is thehop of commerce (see illus.).