Flower profile
Water smartweed
Persicaria amphibia
Water smartweed (Persicaria amphibia) is a flowering plant in the Polygonaceae family, native in the lower 48 states, blooming mostly July–September across the U.S.
Water smartweed is a wildflower that USDA PLANTS lists as native in the lower 48 states.
*iNaturalist research-grade observations, as of October 17, 2026.
On our lists for: North Dakota
Quick look
Persicaria amphibia is a species of flowering plant in the knotweed family known by several common names, including longroot smartweed, water knotweed, water smartweed, and amphibious bistort. It is native to much of North America, Asia, Europe, and parts of Africa, and it grows elsewhere as an introduced species and sometimes a noxious weed.
- It belongs to the Polygonaceae family. iNaturalist
- USDA PLANTS describes it as an herb (forb) with a perennial life cycle. USDA PLANTS
- USDA PLANTS lists it as native in the lower 48 states and records it in 45 states. USDA PLANTS
- NatureServe lists it as native to North Dakota. NatureServe
- iNaturalist has 95 research-grade sightings of it in North Dakota, ranking #72 among the 116 flowers on our North Dakota list. iNaturalist
When does it bloom?
Conservation status
- Federal (U.S. ESA)
- Not listed No U.S. Endangered Species Act listing in the USFWS ECOS database. USFWS ECOS
- NatureServe global
- G5 Secure worldwide. NatureServe
- North Dakota
- No list North Dakota has no state law listing endangered or threatened plants, so we show NatureServe's North Dakota ranks instead. NatureServe: SNR, not yet ranked in North Dakota.
- Rare elsewhere
- Other states where NatureServe ranks it rare or missing: GA (S1). (S1 critically imperiled, S2 imperiled, SH possibly extirpated, SX presumed extirpated.)
Checked October 17, 2026. Rankings and lists can change, so follow the links for the latest.
Can you eat it?
None of the sources we checked (NC State Extension (no page for this plant), USDA PLANTS) say whether it's edible or poisonous for people.
It isn't on the ASPCA plant list.
🌿 Never eat a wild plant unless you're certain of its ID; this isn't medical advice. Worried about a person? Call Poison Control at 1-800-222-1222. Worried about a pet? Call your vet.
Where does it grow?
USDA PLANTS records water smartweed in 45 states plus Washington, D.C.
recorded by USDA PLANTS on our state lists not recorded
See the full list of states
Arizona, Arkansas, California, Colorado, Connecticut, Delaware, Idaho, Illinois, Indiana, Iowa, Kansas, Kentucky, Louisiana, Maine, Maryland, Massachusetts, Michigan, Minnesota, Mississippi, Missouri, Montana, Nebraska, Nevada, New Hampshire, New Jersey, New Mexico, New York, North Carolina, North Dakota, Ohio, Oklahoma, Oregon, Pennsylvania, Rhode Island, South Carolina, South Dakota, Tennessee, Texas, Utah, Vermont, Virginia, Washington, West Virginia, Wisconsin, Wyoming; District of Columbia.
North Dakota counties with USDA records: Barnes, Billings, Bottineau, Bowman, Burke, Burleigh, Cass, Cavalier, Dickey, Divide, Eddy, Emmons, Foster, Grand Forks, Grant, Griggs, Kidder, LaMoure, Logan, McIntosh, McKenzie, McLean, Mercer, Mountrail, Nelson, Pembina, Pierce, Ramsey, Ransom, Renville, Richland, Rolette, Sargent, Sheridan, Slope, Stark, Steele, Stutsman, Traill, Walsh, Ward, Williams.
Names, range and relatives
Native status by region (USDA PLANTS): Canada: Native; Lower 48 states: Native.
Other scientific names (synonyms in USDA PLANTS): Persicaria coccinea, Persicaria muehlenbergii, Polygonum coccineum, Polygonum muehlenbergii.
County records: USDA PLANTS lists it in 904 counties across 38 states; the most are in Illinois (90), Kansas (90), Ohio (62).
Other Persicaria on Bloomipedia (5): American jumpseed, Low smartweed, Mile-a-minute weed, Spotted lady's thumb, Pink knotweed.
More from the Polygonaceae family (21 on Bloomipedia; most observed first): California buckwheat, Japanese knotweed, Sulfur buckwheat, Desert trumpet, American bistort, Cushion buckwheat, Devil's spineflower, Parsnipflower buckwheat.
More North Dakota flowers
Sources
- USDA, NRCS. PLANTS Database, profile POAME.
- iNaturalist, Persicaria amphibia: taxonomy, research-grade observation counts and “Flowering” annotations, retrieved October 17, 2026.
- Wikipedia, Persicaria amphibia (lead quoted under CC BY-SA 4.0).
- North Dakota: North Dakota state noxious weeds (N.D. Admin. Code 7-06-01-02), as listed by the ND Department of Agriculture.
- USFWS, ECOS species database (ESA listing check), October 17, 2026.
- NatureServe Explorer, Persicaria amphibia (global and state ranks).
- Edibility and toxicity: no source found (marked "not well documented").
- Photo: Bob Miller via iNaturalist · CC BY 4.0 · resized.