Japanese hops
Humulus japonicus Siebold & Zucc.

SOURCE: The following information on this species is taken, in part, from the Invasive Plant Atlas of New England website at http://invasives.eeb.uconn.edu/ipane/. Modifications include additional pictures (from www.invasives.org) and resource information. Check the website links for future updates.

DESCRIPTION: Humulus japonicus is a monoecious, annual vine that can grow between 0.5-2.5 m (1.5-8 ft.) in length. The stems and leaves of this plant have a very rough texture. The leaves are cordate in outline and palmately lobed. The leaves have 5 to 9 lobes separated by V-shaped sinuses. The margins of the lobes are serrulate and they have an acuminate apex. The leaves measure 5-12 cm (2-4.75 in.) in length, and the petiole is often longer than the leaf blade itself. The uppermost leaves are often 3-5 lobed.

The staminate inflorescences are erect and measure 15-25 cm (6-10 in.) in length, while the pistilate inflorescences are cone-shaped spikes, 7-10 mm (0.25-0.4 in.) in size and the margins of the bracteoles are densely ciliate. The pistilate spikes are dull green in color and become abruptly acuminate. The flowers bloom in early to midsummer. The achenes are yellow-brown, ovoid-orbicular in shape, and 4-5 mm (0.2 in.) in length.

Page References Bailey 341, Fernald 556, Flora of North America 384, Gleason & Cronquist 73, Holmgren 70, Magee & Ahles 421. See reference section below for full citations.

REPRODUCTIVE/DISPERSAL MECHANISMS: Humulus japonicus reproduces by seed. Its small seeds are dispersed by mechanical means, most notably by wind and by moving water along rivers and streams.

DISTRIBUTION: Humulus japonicus is native to eastern Asia. In North America its range is from southern Quebec and Ontario to northern Georgia and west from North Dakota to Kansas. It is found in all of the states of New England.

HISTORY OF INTRODUCTION IN NEW ENGLAND: It is unclear when Humulus japonicus was first brought to North America, but it probably arrived here due to intentional cultivation. In New England, the earliest records of its escape and naturalization come from eastern Massachusetts and southern Connecticut at the end of the nineteenth century. There are also records from several locations in Vermont (Brattelboro, Burlington, Bellows Falls) from the early part of the twentieth century. Most of these early records note that Humulus japonicus had escaped to "waste places." Robinson (1908) described Humulus japonicus as having "occasionally escaped from frequent cultivation." By 1950, Fernald characterized it as being found in waste places, roadsides and along fencerows from New England to Michigan and south from Virginia and Missouri.

Photos: (L-R): 1 and 2: Chris Evans, The University of Georgia, www.forestryimages.org. (leaves; down-curved bracts and sharp prickles) 3: Fruits: Leslie J. Mehrhoff, University of Connecticut, IPANE, http://invasives.eeb.uconn.edu/ipane/

HABITATS IN NEW ENGLAND: Abandoned Field, Edge, Open Disturbed Area, River or Stream, Roadside, Vacant Lot, Yard or Garden

Humulus japonicus is often found in disturbed areas, along roadsides and utility right-of-ways, and in open fields, particularly when the soil is moist. It is also commonly found along river or stream banks and in flood plain areas, where it can form dense, almost continuous stands.

THREATS: When forming dense stands, Humulus japonicus can out compete native vegetation.

Photo: Leslie J. Mehrhoff, University of Connecticut, IPANE, http://invasives.eeb.uconn.edu/ipane/

For more information on Japanese hops, please contact:
Invasive Plant Atlas of New England, http://invasives.eeb.uconn.edu/ipane/
Mid-Atlantic Exotic Pest Plant Council, Inc., http://www.ma-eppc.org
National Invasive Species Information Center, http://www.invasivespeciesinfo.gov
Plant Conservation Alliance, Alien Plant Working Group, Weeds Gone Wild, http://www.nps.gov/plants/alien/
The Bugwood Network, MA-EPPC Plant List, http://www.invasive.org/maweeds.cfm
The Nature Conservancy, Invasive Species Initiative, http://tncweeds.ucdavis.edu/esadocs.html
USDA Forest Service, Northeastern Area, Invasive Plants: Weeds of the Week, http://www.na.fs.fed.us/fhp/invasive_plants/weeds/
USDA-NRCS PLANTS Database, http://plants.usda.gov/
Virginia Tech Weed Guide, http://www.ppws.vt.edu/weedindex.htm

REFERENCES:
Bailey, L. H. 1949. Manual of Cultivated Plants. Macmillan, New York.
Britton, N. L. and A. Brown. 1970. An Illustrated Flora of the Northeastern United States vol. 1. Dover Publications Inc., New York.
Fernald, M.L. 1950. Gray's Manual of Botany 8th ed. American Book Co., Boston. Flora of North America Editorial Committee, eds. 1993+. Flora of North America North of Mexico. Volume #3. Oxford University Press. Flora of North America Association ed. 2000. Flora of North America vol. 3. Oxford University Press, Oxford, New York.
Gleason H.A. and A.C. Cronquist. 1991. Manual of Vascular Plants of the Northeastern United States and Adjacent Canada. 2nd ed. New York Botanical Garden, Bronx, New York.
Holm, L.G., Pancho, J.V., Herberger, J.P., and Plucknett, D.L. (1979). A Geographical Atlas of World Weeds. John Wiley and Sons, New York, USA. Hydrocharis morsus-ranae
Holmgren N.H. 1998. Illustrated Companion to Gleason and Cronquist's Manual. New York Botanical Garden, Bronx, New York.
Magee D.W and H.E. Ahles. 1999. Flora of the Northeast. University of Massachusetts Press, Amherst.
USDA, NRCS. 2001. The PLANTS Database, Version 3.1. (http://plants.usda.gov). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

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