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Polygonum amphibium var. emersum (Longroot smartweed)
Reveal, James L.

Polygonum amphibium var. emersum

Polygonum amphibium L. var. emersum Michx.

Longroot Smartweed

Polygonaceae (Buckwheat Family)

Synonym(s): Persicaria amphibia, Persicaria amphibia var. emersa, Persicaria coccinea, Persicaria muehlenbergii, Polygonum amphibium var. coccineum, Polygonum coccineum, Polygonum coccineum var. pratincola, Polygonum coccineum var. terrestre, Polygonum muehlenbergii, Polygonum muehlenbergii var. terrestre


USDA Native Status: L48 (N), CAN (N)

Polygonum amphibium var. emersum has lanceolate leaves with narrowly tapering tips and slender flower clusters at least 1 1/2 inches (4 cm) long. Once called P. coccineum, a separate species, this variety of Polygonum amphibium is aggressive to the point of being classified as a noxious weed.


From the Image Gallery

29 photo(s) available in the Image Gallery

Plant Characteristics

Duration: Perennial
Habit: Herb
Fruit Type: Achene
Size Notes: Stems prostrate to ascending to erect, up to about 4 feet long in terrestrial plants, up to about 10 feet in some aquatic plants.

Bloom Information

Bloom Color: Red , Pink
Bloom Time: Jun , Jul , Aug , Sep


USA: AR , AZ , CA , CO , CT , DC , DE , IA , ID , IL , IN , KS , KY , LA , MA , MD , ME , MI , MN , MO , MS , MT , NC , ND , NE , NH , NJ , NM , NV , NY , OH , OK , OR , PA , RI , SC , SD , TN , TX , UT , VA , VT , WA , WI , WV , WY
Canada: AB , BC , MB , NB , NS , NT , PE , QC , SK

Growing Conditions

Aquatic: yes

National Wetland Indicator Status

This information is derived from the U.S. Army Corps of Engineers National Wetland Plant List, Version 3.1 (Lichvar, R.W. 2013. The National Wetland Plant List: 2013 wetland ratings. Phytoneuron 2013-49: 1-241). Click here for map of regions.

Web Reference

Webref 38 - Flora of North America (2019) Missouri Botanical Garden, St. Louis, MO & Harvard University Herbaria, Cambridge, MA.
Webref 23 - Southwest Environmental Information Network (2009) SEINet - Arizona Chapter

Additional resources

USDA: Find Polygonum amphibium var. emersum in USDA Plants
FNA: Find Polygonum amphibium var. emersum in the Flora of North America (if available)
Google: Search Google for Polygonum amphibium var. emersum


Record Modified: 2023-05-02
Research By: TWC Staff

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