The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Reynoutria japonica
(Itadori knotweed)

Copyright Info
Reynoutria japonica (Houtt.) Ronse Decr.

Common name: Itadori knotweed

Taxonomy: available through www.itis.govITIS logo

Native Range:
Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Reynoutria japonica are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
CT189420137Farmington River; Housatonic; Outlet Connecticut River; Quinnipiac; Saugatuck; Shetucket River; Thames
DC194619891Middle Potomac-Anacostia-Occoquan
IL199820052Des Plaines; Lower Fox
IN197919791Middle Wabash-Little Vermilion
LA198719871Bayou D'Arbonne
ME198820147Maine Coastal; Passamaquoddy Bay-Bay of Fundy; Penobscot River; Presumpscot; Saco River; Saint Francis River-Saint John River; St. George-Sheepscot
MD191520084Choptank; Gunpowder-Patapsco; Middle Potomac-Anacostia-Occoquan; Middle Potomac-Catoctin
MA196220107Ashuelot River-Connecticut River; Blackstone River; Cape Cod; Charles; Deerfield River; Narragansett; Westfield River
MI201520205Huron; Muskegon; Shiawassee; St. Joseph; Thunder Bay
MO200520051Lower Missouri-Crooked
NH200220074Black River-Connecticut River; Saco River; Upper Androscoggin River; West River-Connecticut River
NJ192420032Hackensack-Passaic; Raritan
NY190020208Bronx; Hudson-Hoosic; Lower Hudson; Raisin River-St. Lawrence River; Rondout; Saugatuck; Southern Long Island; Upper Delaware
OH200920223Ashtabula-Chagrin; Cuyahoga; Raccoon-Symmes
OR200220226Illinois; Lower Rogue; Middle Fork Willamette; Middle Rogue; Siuslaw; Upper Willamette
PA200220243Middle Delaware-Mongaup-Brodhead; Schuylkill; Upper Delaware
RI193120032Narragansett; Pawcatuck River
VT200120011Otter Creek
VA197319731Middle Potomac-Anacostia-Occoquan
WA200120112Lake Chelan; Lake Washington
WV200820102Cheat; Lower New
WI200820222Lower Wisconsin; Upper Fox

Table last updated 7/20/2024

† Populations may not be currently present.

Impact of Introduction:
Summary of species impacts derived from literature review. Click on an icon to find out more...

EcologicalEconomicHuman Health

Japanese knotweed is listed as one of the “World’s Worst” invaders (Global Invasive Species Database 2021). Once established, this fast-growing species spreads quickly from its deep extensive underground rhizome system (Del Tredici 2017) to form a dense canopy shading out other species (Beerling et al. 1994). A study in a small third order stream in New Jersey found that a stand of Japanese knotweed had a significant impact by decreasing stream baseflow and water levels (Vanderlklein et al. 2014). Japanese knotweed invasions could degrade terrestrial habitat quality for frogs by indirectly reducing arthropod abundance (Maerz et al. 2005). In a laboratory experiment, chemical compounds extracted from Japanese knotweed suppressed the of growth of moss which could have an effect on the moss assemblages in habitats invaded by knotweed (Palmeri and Kiviat 2021).

References: (click for full references)

Barney, J.N. 2006. North American history of two invasive plant species: phytogeographic distribution, dispersal vectors, and multiple introductions. Biological Invasions 8:703–717.
Beerling, D.J., J.P. Bailey, and A.P. Conolly. 1994. Fallopia japonica (Houtt.) Ronse Decraene. Journal of Ecology 82:959–979.

Braatne, J.H., S.M.P. Sullivan, and E. Chamberlain. 2007. Leaf decomposition and stream macroinvertebrate colonisation of Japanese knotweed, and invasive plant species. International Review of Hydrobiology 92:656–665.

Chen, H., T. Tuck, X. Ji, X. Zhou, G. Kelly, A. Cuerrier, and J. Zhang. 2013. Quality assessment of Japanese knotweed (Fallopia japonica) grown on Prince Edward Island as source of resvertarol. Journal of Agricultural and Food Chemistry 61:6383–6392.

Child, L., and M. Wade. 2000. The Japanese knotweed manual: The management and control of an invasive alien weed. Packard Publishing Limited, West Sussex, UK.

Clements, D.R., T. Larsen, and J. Grenz. 2016. Knotweed management strategies in North America with the advent of widespread hybrid bohemian knotweed, regional differences, and the potential for biocontrol via the psyllid Aphalara itadori Shinji. Invasive Plant Science and Management 9:60–70.

De Waal, L.C. 2001. A viability study of Fallopia japonica stem tissue. Weed Research 41:447–460.

Del Tredici, P. 2017. The introduction of Japanese knotweed, Reynoutria japonica, into North America 1. The Journal of the Torrey Botanical Society 144(4):406–416.

Global Invasive Species Database. 2021. Species profile: Polygonum cuspidatum. Downloaded from http://www.iucngisd.org/gisd/species.php?sc=91 on 14-09-2021.

Maerz, J.C., B. Blossey, and V. Nuzzo. 2005. Green frogs show reduced foraging success in habitats invaded by Japanese knotweed. Biodiversity and Conservation 14:2901–2911.

Palmeri, J. and E. Kiviat. 2021. Toxic effects of knotweed Polygonum cuspidatum s.l. rhizome on the mosses Atrichum angustatum and Thuidium delicatulum. Lindbergia 44: linbg.01131.

Richards, C.L., R.L. Walls, J.P. Bailey, R. Parameswaran, T. George, and M. Pigliucci. 2008. Plasticity in salt tolerance traits allows for invasion of novel habitat by Japanese knotweed s.l. (Fallopia japonica and F. bohemica, Polygonaceae). American Journal of Botany 95(8):931–942.

Shaw, R.H., S. Bryner, and R. Tanner. 2009. The life history and host range of the Japanese knotweed psyllid, Aphalara itadori Shinji: Potentially the first classical biological weed control agent for the European Union. Biological Control 49:105–113.

United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS). 2021. Polygonum cuspidatum Siebold & Zucc. plant profile. https://plants.usda.gov/home/plantProfile?symbol=POCU6 (accessed 21 September 2021).

Vanderlklein, D.W., J. Galster, and R. Scherr. 2014. The impact of Japanese knotweed on stream baseflow. Ecohydrology 7:881–886.

Winston, R.L., C.B. Randall, B. Blossey, P.W. Tipping, E.C. Lake, and J. Hough-Goldstein. 2017. Field Guide for the Biological Control of Weeds in Eastern North America. USDA Forest Service, Forest Health Technology Enterprise Team, Morgantown, West Virginia, USA.

Author: Brown, M.

Revision Date: 10/21/2021

Citation Information:
Brown, M., 2024, Reynoutria japonica (Houtt.) Ronse Decr.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=3602, Revision Date: 10/21/2021, Access Date: 7/20/2024

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [7/20/2024].

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