2. Humulus Linnaeus, Sp. Pl. 2: 1028. 1753; Gen. Pl. ed. 5, 453, 1754.
Hop, houblon [Latin humulus, applied to hop plant]
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.
Species 3 (2 in the flora): temperate Northern Hemisphere.
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.
