Persicaria wallichii - Greuter & Burdet
Himalayan Knotweed
Synonym(s): Polygonum polystachyum Wallich ex Meisn.
Taxonomic Status: Accepted
Related ITIS Name(s): Polygonum polystachyum Wallich ex Meisn. (TSN 20919)
French Common Names: renouée à épis nombreux
Unique Identifier: ELEMENT_GLOBAL.2.148595
Element Code: PDPGN0L1Z0
Informal Taxonomy: Plants, Vascular - Flowering Plants - Buckwheat Family
 
Kingdom Phylum Class Order Family Genus
Plantae Anthophyta Dicotyledoneae Polygonales Polygonaceae Persicaria
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Concept Reference
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Concept Reference: Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
Concept Reference Code: B94KAR01HQUS
Name Used in Concept Reference: Polygonum polystachyum
Taxonomic Comments: FNA (vol. 5, 2005) transfers Polygonum polystachum to Persicaria wallichii.
Conservation Status
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NatureServe Status

Global Status: GNR
Global Status Last Changed: 22Mar1994
Rounded Global Status: GNR - Not Yet Ranked
Nation: United States
National Status: NNA
Nation: Canada
National Status: NNA (13Nov2017)

U.S. & Canada State/Province Status
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United States California (SNA), Massachusetts (SNR), Oregon (SNA)
Canada British Columbia (SNA), Nova Scotia (SNA)

Other Statuses

NatureServe Global Conservation Status Factors

Other NatureServe Conservation Status Information

Distribution
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U.S. States and Canadian Provinces

Due to latency between updates made in state, provincial or other NatureServe Network databases and when they appear on NatureServe Explorer, for state or provincial information you may wish to contact the data steward in your jurisdiction to obtain the most current data. Please refer to our Distribution Data Sources to find contact information for your jurisdiction.
Color legend for Distribution Map
NOTE: The distribution shown may be incomplete, particularly for some rapidly spreading exotic species.

U.S. & Canada State/Province Distribution
United States CAexotic, MA, ORexotic
Canada BCexotic, NSexotic

Range Map
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Ecology & Life History Not yet assessed
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Economic Attributes Not yet assessed
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Management Summary Not yet assessed
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Population/Occurrence Delineation Not yet assessed
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Population/Occurrence Viability
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U.S. Invasive Species Impact Rank (I-Rank)
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Disclaimer: While I-Rank information is available over NatureServe Explorer, NatureServe is not actively developing or maintaining these data. Species with I-RANKs do not represent a random sample of species exotic in the United States; available assessments may be biased toward those species with higher-than-average impact.

I-Rank: High/Medium
Rounded I-Rank: High
I-Rank Reasons Summary: Polygonum polystachyum, Himalayan knotweed, is known in the United States mainly from the Pacific Northwest. It has invaded riparian areas and other wetland places along the North and Central coast from Washington to California (also British Columbia). It also occurs in Massachusetts, but it is unclear if this species is spreading the eastern United States. This species reproduces vegetatively, fragmenting and resprouting easily. It also grows very quickly and outcompetes native plant species. It is difficult to control and requires at least 2 or 3 years to eradicate.
Subrank I - Ecological Impact: High/Medium
Subrank II - Current Distribution/Abundance: Medium/Low
Subrank III - Trend in Distribution/Abundance: Medium
Subrank IV - Management Difficulty: Medium/Low
I-Rank Review Date: 15Mar2004
Evaluator: Oliver, L.
Native anywhere in the U.S?
Native Range: Polygonum polystachyum is native to Asia, including Afghanistan, China, Bhutan, India, Nepal, Pakistan and Myanmar (GRIN).

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Screening Questions

S-1. Established outside cultivation as a non-native? YES
Comments: This knotweed species is known from California, Oregon and Massachusetts (Kartesz 1999). This species has also been reported in Washington (WA State Noxious Weed Control Board).

S-2. Present in conservation areas or other native species habitat? Yes
Comments: Polygonum polystachyum is a wetland plant that invades moist sites including roadsides, riparian and wetland areas (WA State Noxious Weed Contol Board).

Subrank I - Ecological Impact: High/Medium

1. Impact on Ecosystem Processes and System-wide Parameters:High/Moderate significance
Comments: Polygonum polystachyum, as well as other knotweeds, is known to choke small streams and other waterways, thereby altering the hydrologic regime.

2. Impact on Ecological Community Structure:Moderate significance
Comments: Himalayan knotweed, and other exotic knotweeds, is known to grow so thickly that it creates dense shade so that the establishment of tree seedlings on riverbanks is prevented (Skamania County, Washington, Noxious Weeds). This ultimately prevents the tree layer along riparian areas from regenerating itself.

3. Impact on Ecological Community Composition:High significance
Comments: Exotic knotweeds, including P. polystachyum, can produce dense stands, and even monocultures, which ultimately exclude native vegetation (Skamania County, Washington, Noxious Weeds, WA State Noxious Weed Control Board, University of California, Encycloweedia). Also, exotic knotweeds are known to be allelopathic, meaning its roots produce substances which are toxic to other plants, so germination and growth of other plant species is thwarted (Skamania County, Washington, Noxious Weeds).

4. Impact on Individual Native Plant or Animal Species:Unknown

5. Conservation Significance of the Communities and Native Species Threatened:Medium/Low significance
Comments: Himalayan knotweed impacts riparian areas (Skamania County, Washington, Noxious Weeds; WA State Noxious Weed Control Board 2003). It is known to exclude native species (Skamania County, Washington, Noxious Weeds).

Subrank II. Current Distribution and Abundance: Medium/Low

6. Current Range Size in Nation:Low significance
Comments: This knotweed species is known from Washington (WA State Noxious Weed Control Board 2003), Oregon, California and Massachusetts (Kartesz 1999).

7. Proportion of Current Range Where the Species is Negatively Impacting Biodiversity:High/Low significance
Comments: This species is a significant threat to riparian habitats in Kittitas County, Washington (WA State Noxious Weed Control Board 2003).

8. Proportion of Nation's Biogeographic Units Invaded:Low significance
Comments: Polygonum polystachyum prefers to grow in a moist climate and specifically inhabits the North and Central coastline from Canada to California (WA State Noxious Weed Control Board 2003). It also occus in Massachusetts, which contains 2 ecoregions (TNC 2001).

9. Diversity of Habitats or Ecological Systems Invaded in Nation:Low significance
Comments: Polygonum polystachyum has invaded riparian and wetland areas. Specifically, this species grows in open, sunny areas on moist soil in cool temperate climates. It also tolerates a wide range of soil types (WA State Noxious Weed Control Board 2003).

Subrank III. Trend in Distribution and Abundance: Medium

10. Current Trend in Total Range within Nation:Moderate significance
Comments: Polygonum polystachyum has been reported as uncommon in California, except perhaps in North and Central coastline. In Washington, this species has been reported as spreading vigoroursly (Whatcom Weeds, Whatcom County, Washington).

11. Proportion of Potential Range Currently Occupied:Medium significance/Insignificant
Comments: This species is known to require cool temperate climates, and has invaded every state in th Pacific Northwest, including British Columbia (University of California, Encycloweedia 2003). It has also invaded Massachusetts, which perhaps indicates it could spread into other states in New England.

12. Long-distance Dispersal Potential within Nation:High/Moderate significance
Comments: Polygonum polystachyum reproduces vegetatively and sexually, however, it appears that is spreads most often by vegetative means. It has been documented that vegetative parts of knotweeds, including the Himalayan knotweed, can be carried by floodwaters which then are able to grow roots and establish themselves on in floodplains and cobble bars (Skamania County, Washington, Noxious Weeds).

13. Local Range Expansion or Change in Abundance:Moderate significance
Comments: This knotweed species appears to be spreading at least in Washington state. Kartesz 1999 does not have a report for the species in that state, however, the Washington State Noxious Weed Control Board has listed it as a noxious weed for control in Kittitas County (WA State Noxious Weed Control Board 2003).

14. Inherent Ability to Invade Conservation Areas and Other Native Species Habitats:Medium/Low significance
Comments: Himalayan knotweed appears to be well adapted for invading wetland and riparian habitats, especially in the Pacific Northwest, as it has invaded and spread to each state in region. It reproduces vegetatively and fragments of the plant body can travel through waterways either by flood or usual hydrologic processes and become established (Skamania County, Washington, Noxious Weeds).

15. Similar Habitats Invaded Elsewhere:Moderate significance
Comments: In its native range, this species inhabits wet meadows and marshes of forested areas between 2500 and 4000 m in elevation (University of California, Encycloweedia 2003). If this species were to be introduced into other areas of the country with cool temperate climates and wet meadows or wooded marshes, it may be able to spread to those habitats in the United States.

16. Reproductive Characteristics:High significance
Comments: Polygonum polystachyum reproduces vegetatively and fragments easily, produces an extensive network of rhizomes which easily resprout and grows faster than native species (Skamania County, Washington, Noxious Weeds).

Subrank IV. General Management Difficulty: Medium/Low

17. General Management Difficulty:Moderate significance
Comments: The Himalayan knotweed has "populations [that] are extremely persistent and colonies are extremely difficult to eradicate" (WA State Noxious Weed Control Board 2003). Knotweeds require at least 2 or 3 years of active managment for well established patches. Usually more than one method of control has to be applied (Skamania County, Washington, Noxious Weeds).

18. Minimum Time Commitment:Low significance
Comments: As mentioned above well established patches of this species and other knotweeds require at least 2 to 3 years of management (Skamania County, Washington, Noxious Weeds).

19. Impacts of Management on Native Species:Unknown

20. Accessibility of Invaded Areas:Unknown
Authors/Contributors
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Botanical data developed by NatureServe and its network of natural heritage programs (see Local Programs), The North Carolina Botanical Garden, and other contributors and cooperators (see Sources).

References
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  • California Dept. of Food and Agriculture. 2003. Last updated December 13, 2003. EncycloWeedia: Notes on identification, biology, and management of plants defined as Noxious Weeds by California law. Available at: http://www.cdfa.ca.gov/phpps/ipc/encycloweedia/encycloweedia_hp.htm. (Accessed 2004).

  • Douglas, G.W., D. Meidinger, and J. Pojar, eds. 1999. Illustrated Flora of British Columbia, Vol. 4, Dicotyledons (Orobanchaceae through Rubiaceae). B.C. Minist. Environ., Lands and Parks, and B.C. Minist. For., Victoria. 427pp.

  • Flora of North America Editorial Committee. 2005. Flora of North America North of Mexico. Vol. 5. Magnoliophyta: Caryophyllidae: Caryophyllales, Polygonales, and Plumbaginales. Oxford Univ. Press, New York. vii + 656 pp.

  • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.

  • Kartesz, J.T. 1999. A synonymized checklist and atlas with biological attributes for the vascular flora of the United States, Canada, and Greenland. First edition. In: Kartesz, J.T., and C.A. Meacham. Synthesis of the North American Flora, Version 1.0. North Carolina Botanical Garden, Chapel Hill, N.C.

  • Skamania County, Washington, Noxious Weeds. 2004. Controlling Knotweeds of the Pacific Northwest. Online. http://www.skamaniacounty.org/Noxious_Weeds/TNCreport.htm and http://skamaniacounty.org/Noxious_Weeds/landownerknotweedinfo.htm. Accessed on 3/15/2004.

  • The Nature Conservancy. 2001. Map: TNC Ecoregions of the United States. Modification of Bailey Ecoregions. Online . Accessed May 2003.

  • USDA, ARS, National Genetic Resources Program. 2001. Germplasm Resources Information Network - (GRIN). [Online Database]. National Germplasm Resources Laboratory, Beltsville, Maryland.URL: http://www.ars-grin.gov/var/apache/cgi-bin/npgs/html/taxon.pl?6438. (Accessed 2004)

  • Washington State Noxious Weed Control Board. 2003. Himalayan Knotweed (Polygonum polystachyum). Written Findings of the State Noxious Weed Control Board - Class A. Online. http:// www.nwcb.wa.gov/weed_info/hykntweed.html. Accessed 3/15/2004.

  • Washington State University. Knotweeds Japanese knotweed, Polygonum cuspidatum; Giant Knotweed, Polygonum sachalinense; Himalayan knotweed, Polygonum polystachyum. Whatcom Weeds. Whatcom County Noxious Weed Control Board, Bellingham, WA. Online: http://www.co.whatcom.wa.us/publicworks/pdf/weeds/knotweeds2.pdf. Accessed on 3/15/2004.

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