Herbs, taprooted annuals or rhizomatous perennials, rightward-twining. Stems usually branched, armed with rigid 2-branched, stalked hairs that facilitate climbing. Leaves simple; petioles often twining, with 2-branched hairs. Leaf blade mostly cordate, palmately lobed, sometimes unlobed; surfaces abaxially resin-dotted and×or gland-dotted. Inflorescences: staminate inflorescences axillary and terminal, cymose panicles, erect to pendent, (10-)20-100+-flowered, flowers small; pistillate axillary, spikes or racemes, flowers solitary or paired, short-pedicellate, subtended by bracts and bracteoles. Staminate and pistillate flowers usually on different plants. Achenes lenticular or terete, ensheathed by brownish or sometimes mottled persistent perianth; embryo coiled. x = 10.

Distribution

Temperate Northern Hemisphere.

Discussion

Species 3 (2 in the flora).

Selected References

Small, E. 1978. A numerical and nomenclatural analysis of morpho-geographic taxa of Humulus. Syst. Bot. 3: 37-76.

Small, E. 1980. The relationships of hop cultivars and wild variants of Humulus lupulus. Canad. J. Bot. 58: 676-686.

Lower Taxa

Humulus japonicus, Humulus lupulus

Key

1	Veins on abaxial surfaces of leaf blades pubescent, with stiff hairs; marginal areas of adaxial surfaces of younger leaf blades with stiff cystolithic hairs; petioles usually longer than blades; margins of pistillate bracteole densely ciliate-hairy; anthers without glands.	Humulus japonicus
1	Veins on abaxial surfaces of leaf blades glabrous or with soft pubescence, without straight, erect hairs; marginal areas of adaxial surfaces of younger leaf blades with few or no cystolithic hairs; petioles usually shorter than blades; margins of pistillate bracteole not ciliate-hairy; anthers glandular.	Humulus lupulus