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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.

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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. 2009. The PLANTS Database (http://plants.usda.gov, 23 Mar 2017). National Plant Data Center, Baton Rouge, LA 70874-4490 USA.

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Site: BWCAW Date: 2005-September-01Photographer: Gerald C Williamson
Minolta Dimage Z2
1/100f/3.2 ISO80
11.1mm
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
6.3mm
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

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2017
Photographs Copyright owned by the named photographer