USDA PLANTS Symbol: FAJA2
U.S. Nativity: Exotic
Habit: Forbs/Herbs Vines
Fallopia japonica (Houttuyn) Ronse-Decraene

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Taxonomic Rank: Magnoliopsida: Polygonales: Polygonaceae

Japanese knotweed is a dense growing shrub reaching heights of 10 ft. (3 m). The semi-woody stem is hollow with enlarged nodes. Leaves are alternate, 6 in. (15.2 cm) long, 3-4 in. (7.6-10 cm) wide and broadly-ovate. Flowering occurs in late summer, when small, greenish-white flowers develop in long panicles in the axils of the leaves. Plants are dioecious (male and female flowers occur on separate plants). Japanese knotweed commonly invades disturbed areas with high light, such as roadsides and stream banks. Reproduction occurs both vegetatively (rhizomes) and seeds, making this plant extremely hard to eradicate. The dense patches shade and displace other plant life and reduce wildlife habitat. Japanese knotweed resembles giant knotweed (Polygonum sachalinense), but giant knotweed is larger and has heart-shaped leaves. Japanese knotweed is native to eastern Asia and was first introduced into North America in the late 1800s.

Identification, Biology, Control and Management Resources

Selected Images from Invasive.orgView All Images at Invasive.org


Flower(s);
Jan Samanek, Phytosanitary Administration, Bugwood.org
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Plant(s);
Nanna Borcherdt, Sitka Conservation Society, Bugwood.org
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Stem(s); stem and leaves in July
Steve Manning, Invasive Plant Control, Bugwood.org
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Foliage; Comparison of leaves of P. sachalinense (right of each pair) and P. cuspidatum
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Flower(s);
Leslie J. Mehrhoff, University of Connecticut, Bugwood.org
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Fruit(s);
Jan Samanek, Phytosanitary Administration, Bugwood.org
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Fruit(s); fruit
Jil Swearingen, USDI National Park Service, Bugwood.org
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Seed(s);
Ken Chamberlain, The Ohio State University, Bugwood.org
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Stem(s); In September
James H. Miller, USDA Forest Service, Bugwood.org
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Stem(s);
Chris Evans, University of Illinois, Bugwood.org
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Infestation; October, 2007.; Nathan Guyton and Japanese Knotweed
Randy Westbrooks, Invasive Plant Control, Inc., Bugwood.org
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Seedling(s);
Ohio State Weed Lab , The Ohio State University, Bugwood.org
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Plant(s); Britton, N.L., and A. Brown. 1913. Illustrated flora of the northern states and Canada. Vol. 1: 676.
USDA PLANTS Database, USDA NRCS PLANTS Database, Bugwood.org
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EDDMapS Distribution:
This map is incomplete and is based only on current site and county level reports made by experts and records obtained from USDA Plants Database. For more information, visit www.eddmaps.org
 


State(s) Where Reported invasive.
Based on state level agency and organization lists of invasive plants from WeedUS database.


Invasive Listing Sources: