hop, herbaceous perennial vine of the family Moraceae (mulberry family), widely cultivated since early times for brewing purposes. The commercial hop ( Humulus lupulus ) is native to Eurasia but is now grown in many temperate regions, notably England, Germany, the United States, South America, and Australia. The conelike mature female flowers, called hops, are borne on different plants from the male; their loose scales contain lupulin, a yellow resinous powder that is added to beer to impart a bitter flavor and is used medicinally as a tonic and soporific. Oil of hops is used for some perfumes, and the hop stem is used for fiber. The fruit of the unrelated hop tree ( Ptelea trifoliata ) of North America is occasionally used as a substitute for hops. Hops are classified in the division Magnoliophyta, class Magnoliopsida, order Urticales, family Moraceae.