2.
Humulus lupulus
Linnaeus, Sp. Pl. 2: 1028. 1753.
Hop(s), common hop(s), houblon
Herbs , perennial, rhizomatous, 1-6(-7) m. Stems branched. Leaves: petioles usually shorter than blades. Leaf blade ± cordate, palmately 3-7-lobed, sometimes unlobed, 3-15 cm, margins dentate-serrate; surfaces abaxially with veins glabrous or with soft pubescence, without straight, erect hairs, glands yellow, adaxially margins of younger leaf blades with few or no cystolithic hairs. Inflorescences: staminate with flowers whitish to yellowish, anthers glandular; pistillate usually racemes, 10-20 mm, pedunculate; bracteole margins not ciliate-hairy. Infructescences pendulous, pale yellow, conelike, ovoid to oblong, (1-)2-3(-6) cm; bracteoles with yellow glands. Achenes yellowish, ovoid, compressed, glandular. 2 n = 20, including 2 or more sex-determining chromosomes.
Varieties 5 (4 in the flora): North America.
Until recently, knowledge of the existence of indigenous kinds of North American Humulus lupulus was uncertain, although the appellation American hop was applied sometimes to H . lupulus var. neomexicanus and sometimes confusingly to other hop varieties. The distinctive Japanese variety H . lupulus var. cordifolius (Miquel) Maximowicz has not been collected from North America. Hops cultivated commercially in North America for flavoring alcoholic beverages are forms of the European H . lupulus var. lupulus . The European variety may have been introgressed by one of the American varieties.
Humulus lupulus has often been transplanted from the wild to homesites as an ornamental. When such sites are abandoned, the plants often persist, and it may appear that they are present naturally. As well, suppliers of ornamental plants may sell hops collected from one site to buyers in a quite distant site. The hop varieties discussed here may therefore be found occasionally beyond the distribution ranges given in this treatment.
Native Americans used Humulus lupulus medicinally to induce sleep, for breast and womb problems, for inflamed kidneys, rheumatism, bladder problems, intestinal pain, fever, earaches, pneumonia, coughs, and nervousness, as a tonic and a stimulant, and as a witchcraft medicine (D. E. Moerman 1986).
The measurements mentioned in couplet 1 of the following key are taken in the middle abaxial portion of the central lobe on 4-6 cm leaf blades attached to flowering or fruiting twigs.
