| Japanese knotweed | USDA PLANTS SYMBOL: FAJA2 |
| Fallopia japonica Sieb. & Zucc. | |
| Synonym(s): fleeceflower, Japanese bamboo | |
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. |
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Identification, Biology, Control and Management Resources
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| Selected Images from Invasive.org | View All Images at Invasive.org |
 Infestation; Mark Frey, The Presidio Trust , Bugwood.org Additional Resolutions & Image Usage |
 Infestation; James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Patch is over 100 m long and up to 15 m wide. Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Foliage; Jack Ranney, University of Tennessee, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Tom Heutte, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage |
 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 Additional Resolutions & Image Usage |
 Plant(s); Theodore Webster, USDA Agricultural Research Service, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); July James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); July James H. Miller, USDA Forest Service, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage |
 Flower(s); Richard Old, XID Services, Inc., Bugwood.org Additional Resolutions & Image Usage |
 Stem(s); stem and leaves in July Steve Manning, Invasive Plant Control, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; infestation in right-of-way in May Steve Manning, Invasive Plant Control, Bugwood.org Additional Resolutions & Image Usage |
 Fruit(s); Jan Samanek, State Phytosanitary Administration, Bugwood.org Additional Resolutions & Image Usage |
 Fruit(s); Ken Chamberlain, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Seed(s); Ken Chamberlain, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org Additional Resolutions & Image Usage |
 Feature(s); new shoots forming Philip Rusted, Thurlow Countryside Management (r&d), Bugwood.org Additional Resolutions & Image Usage |
 Stem(s); Cross-section of Stems Leslie J. Mehrhoff, University of Connecticut, Bugwood.org Additional Resolutions & Image Usage |
 Stem(s); John Cardina, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Stem(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Root(s); Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Root(s); John Cardina, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Seedling(s); cotyledons Ohio State Weed Lab Archive, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Plant(s); Catherine Herms, The Ohio State University, Bugwood.org Additional Resolutions & Image Usage |
 Infestation; Picture within stand Jenn Grieser, New York City Department of Environmental Protection, Bugwood.org Additional Resolutions & Image Usage |