Wildflowers of the United States

Home Journal Family Index - All States Photo Albums News About Privacy

Water Knotweed, Swamp Smartweed, Water Smartweed - Persicaria amphibia

Family: Polygonaceae - Buckwheat family Genus Common Name: Smartweed Native Status: Native
Persicaria amphibia - Water Knotweed, Swamp Smartweed, Water Smartweed. The Polygonum genus has recently been split into multiple genera, with about 30 species being reclassified in the genus Persicaria. I am following the lead of others in changing this from Polygonum amphibium to Persicaria amphibia. The genus common name for Persicaria is now "Smartweed"; Polygonum had been "Knotweed". The text imbedded in the photos will continue to reflect the old classification.

There are aquatic and terrestrial varieties of Persicaria amphibia; the aquatic variety is more widespread than the terrestrial variety than the terrestrial variety, with the terrestrial variety not generally being found in the Southeast. Leaves are alternate and lanceolate.

Leave comments on Persicaria amphibia at this link.

Check here for more information about Persicaria amphibia.
Persicaria amphibia

Distribution of Persicaria amphibia in the United States and Canada:
USDA Plants Distribution Map temporarily unavailable.
Blue=Native; Grey=Introduced

Map from USDA Plants Database:
USDA, NRCS. 2017. The PLANTS Database (http://plants.usda.gov, 24 Feb 2018). National Plant Data Team, Greensboro, NC 27401-4901 USA.

Search Our Database: Enter any portion of the Scientific, Common Name, or both.
Scientific name:
Common name:

Example: Enter "lob" in the common name field and you'll get all our species that have "lobelia" in the common name, as well as "sharp-lobed hepatica".

Do a general Google search of the entire site:

Follow on Twitter
Follow USWildflowers on Twitter

Site: BWCAW Date: 2005-September-01Photographer: Gerald C Williamson
Minolta Dimage Z2
1/100f/3.2 ISO80
Pink flowers are around 1/8-inch across in an ovate or elongated terminal cluster. The blossom have 5 petal-like pink sepals and 5 stamens which extend well beyond the sepals.
Persicaria amphibia

Site: BWCAW Date: 2005-September-01Photographer: Gerald C. Williamson
1/50f/3.2 ISO50
This might be the aquatic variety at a time of low water. Generally the terrestrial has a more elongated flower cluster.
Click on the photo for a larger image
Persicaria amphibia

Commercial / Cookie Notice

Looking for Wildflowers for a specific state? Check here:

All content except USDA Plants Database map Copyright Gerald C. Williamson 2018
Photographs Copyright owned by the named photographer