This section is from the book "An Illustrated Flora Of The Northern United States, Canada And The British Possessions Vol1", by Nathaniel Lord Britton, Addison Brown. Also available from Amazon: An Illustrated Flora of the Northern United States, Canada and the British Possessions. 3 Volume Set..
Twining herbaceous perennial rough vines, with broad opposite thin petioled palmately veined serrate 3-7-lobed or undivided leaves, lanceolate membranous persistent stipules, and dioecious axillary flowers, the staminate panicled, the pistillate in ament-like drooping clustered spikes. Staminate flowers with a 5-parted calyx, the segments distinct and imbricated, and 5 short erect stamens. Pistillate flowers in 2's in the axil of each bract of the anient, consisting of a membranous entire perianth, clasping the ovary, and 2 filiform caducous stigmas. Fruiting aments cone-like, the persistent bracts subtending the compressed ovate achenes. Embryo spirally coiled. [Name said to be the diminutive of the Latin humus, earth.]
Two species, widely distributed through the north temperate zone. Type species: Humulus Lupulus L.
Humulus Lupulus L. Sp. PI. 1028. 1753.
A dextrorsely twining or prostrate vine, often 250 long, very rough with stiff reflexed hairs. Leaves orbicular or ovate in outline, slender-petioled, deeply 3-7-cleft or some of the upper ones ovate, acute and merely serrate; petioles 1/2'-3' long; stipules reflexed, ovate or lanceolate, acuminate, 4"-12" long; panicles of staminate flowers 2'-5' long; ripe pistillate clusters (hops) 1'-2 1/2' long; fruiting bracts broadly ovate, concave, thin, glabrous or nearly so, obtuse, much longer than the achenes; fruiting calyx and achene strongly resinous-aromatic.
In thickets and on river banks, Nova Scotia to Manitoba, south to southern New York, Pennsylvania, Georgia, Kansas, Arizona and New Mexico. Extensively escaped from cultivation. Native also of Europe and Asia. July-Aug. Fruit ripe Sept.-Oct.
Humulus japonicus Sieb. & Zucc, the Japanese hop, with deltoid acuminate, not resinous, bracts, has escaped from cultivation from Connecticut to New Jersey.