Water smartweed, water knotweed, longroot smartweed
All the western states
Low - grows sideways, often floating on water; stems may be 9 feet long
In or alongside water; lakes, ponds, streams, marshes and moist meadows; up to 9,500 feet
Ovate or lanceolate, up to 5 inches long. Alternate. Stalked
June to September
Persicaria amphibia is an amphibious plant, usually growing semi-submerged along the edge of lakes or on land, in marshy areas and meadows; it has large, shiny green leaves and dense, elongated (up to 6 inches) clusters of small pink flowers, at the end of short stalks. Stems may be hairless or have a covering of short or long hairs. Leaves are oval-shaped for aquatic plants and more lanceolate for those on land, where the stems grow upwards more than sideways, and can reach heights of 3 feet.
Individual flowers have five lobes, opening to reveal either five thin white stamens (which may be slightly exserted), or two styles - plants produce either staminate of pistillate flowers.