Humulus

Linnaeus

Sp. Pl. 2: 1028. 175.

,

Gen. Pl. ed. 5, 453. 1754.

Common names: Hop houblon
Etymology: Latin humulus, applied to hop plant
Treatment appears in FNA Volume 3.

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).

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