Humulus japonicus Siebold & Zucc.
Humulus scandens auct. non (Lour.) Merr.
Japanese hops is native to temperate regions of eastern Asia—China, Japan, Korea, Taiwan and the Russian Federation—as well as to tropical Vietnam. It was probably imported for cultivation, but it escaped and spread quickly. It is related to the variety of hops, Humulus lupulus, used for flavoring and preserving beer, and may be used as a less suitable substitute for this purpose. Japanese hops is considered an invasive in Connecticut, Delaware, Indiana, Maryland, Pennsylvania, Virginia, and the District of Columbia.
Identification: This fast-growing vine has tiny hooks on its stems and leaves that allow it purchase on nearly anything it encounters, reaching between 3-20' (91-609 cm) in length. If you want to get technical, Japanese hops are bines, not vines: they climb with little hooks rather than wrapping tendrils around things like grapes, or using suckers like ivy. Stems are green or reddish purple, with ridges running along the length of the stem. Leaves are rough, with short hairs and 5-9 palmate lobes, and are 2-6" (5-15 cm) in size, with long petioles (stems). Plants are dioecious. Male plants have large cone-shaped panicles up to 10" (25 cm) long and 5" (12 cm) wide; female flowers are about 1" (2.5 cm) long. Though the panicles are large, the flowers are pale and unremarkable, each about ⅛" (3.2 mm) in size. They appear early to mid-summer.
Humulus japonicus at Illinois Wildflowers
Humulus japonicus at the University of Wisconsin's Robert W. Freckmann Herbarium
Humulus japonicus on the Plant Conservation Alliance’s Alien Plant Working Group Least Wanted List
Humulus japonicus on the Virginia Tech Weed Identification Guide
Humulus japonicus on www.eddmaps.org
Humulus japonicus on Plants for a Future, a resource and information centre for edible and otherwise useful plants
Humulus japonicus on eFloras
Humulus japonicus description by Thomas H. Kent, last updated 3 Sep 2013.