Water Smartweed

(Polygonum amphibium)

Water Smartweed (Polygonum amphibium  L.)

Identification: An aquatic or semi-aquatic plant, extremely variable in all of its features. Flowers white to pink, in a tightly cluster head. Flower head short and ovate to elongate. Stem smooth, either upright (in shoreline forms) to floating on the surface of the water. Leaves elongate, broadest in the middle, tapering at either end. Petioles distinct, longest in floating forms, becoming short to nearly absent in shoreline forms. Junction of leaf petiole and stem swollen with a sheath surrounding the stem. Upright forms 1 to 3 feet in height.

Distribution: Throughout most North America except for the southeastern United States.

Habitat: Water Smartweed is an aquatic or semi-aquatic species. Aquatic forms have the stems floating in water, while those closer to the mudflats of the shoreline may be more upright. The species is found along the shores of ponds, lakes, and rivers.

Flowering period: June to September.

Similar Species: Water Smartweed is an exceedingly variable species whose morphology depends in part on how submersed the plant is. The species is usually easily identified by its semi-aquatic to aquatic life style.