Japanese hop
Humulus japonicus Siebold & Zucc.

Overview

Appearance

Humulus japonicus is an annual, climbing or trailing vine that is native to eastern Asia. This vine has 5-lobed leaves (generally), downward pointing prickles on the stem and bracts at the base of the petioles.

Foliage

Leaves are opposite, rough, 2-5 in. (5-13 cm) long, 5-9 lobed with toothed margins. Most leaves will have five lobes, but the upper leaves may only have three.

Flowers

Flowers originate in the leaf axils and are green with five petals. Male and female flowers occur on separate plants (dioecious). Female flowers occur in cone-shaped clusters that hang down and the male flowers occur in upright flower stems.

Fruit

Fruit is a yellow-brown ovoid achene. The small seeds are distributed by wind and water.

Ecological Threat

These vines can grow to 35 ft. (10.7 m) in one growing season, allowing them to infest large areas crowding and out competing native vegetation. Humulus japonicus was introduced into North America in the mid-to-late 1800s as an ornamental.

Resources

• Weed of the Week - USDA Forest Service
• Weeds Gone Wild Fact Sheet - Plant Conservation Alliance, Alien Plant Working Group
• Plant Invaders of Mid-Atlantic Natural Areas - National Park Service

Selected Images

Maps

Invasive Listing Sources

• Connecticut Invasive Plant List
• Connecticut Invasive Plant Working Group
• Connecticut Noxious Weeds
• Indiana Invasive Species Council - Invasive Plant List
• Invasive Plant Species of West Virginia
• Jil M. Swearingen, Survey of invasive plants occurring on National Park Service lands, 2000-2007
• John Randall, The Nature Conservancy, Survey of TNC Preserves, 1995.
• Kentucky Exotic Pest Plant Council - Significant Threat
• Maryland Department of Agriculture's Candidates for Listing of Invasive Plants
• Maryland Department of Natural Resources Policy: Restriction on Planting Exotic Invasive Plants
• Maryland Invasive Species Council - Invasive Species of Concern in Maryland
• Massachusetts Invasive Plants Advisory Group List
• Massachusetts Noxious Weeds
• Massachusetts Prohibited Plant List
• Mid-Atlantic Field Guide to Aquatic Invasive Species
• Minnesota Noxious Weeds
• Missouri SRISP Species List
• National Park Service, Mid-Atlantic Exotic Plant Management Team Invasive Plant List
• New Jersey Invasive Species Strike Team 2017 Invasive Species List
• New York Regulated and Prohibited Invasive Species - Prohibited
• Non-Native Invasive Plants of Arlington County, Virginia
• Nonnative Invasive Species in Southern Forest and Grassland Ecosystems
• Pennsylvania Department of Conservation and Natural Resources Invasive Plants
• Pennsylvania's Field Guide to Aquatic Invasive Species
• Plant Invaders of Mid-Atlantic Natural Areas
• South Carolina Exotic Pest Plant Council
• Tennessee Exotic Pest Plant Council
• Virginia Invasive Plant Species List
• WeedUS - Database of Plants Invading Natural Areas in the United States
• West Virginia Native Plant Society, Flora West Virginia Project, and West Virginia Curatorial Database System, September 3, 1999
• Wisconsin's Invasive species rule – NR 40

References