swamp smartweed Persicaria amphibium L.
Family: Polygonaceae (smartweed)
Life cycle: Perennial, reproduces by seed and creeping rootstocks.
Habitat: wetlands, roadside ditches, poorly drained areas of crop fields
General description: Recumbent to erect stems reaching lengths of up to 3 ft. Stems with swollen nodes have prominent ochrea, rooting at lower nodes of the plant. Leaves are lanceolate with round base and pointed tip, up to 8 in long. Pubescence of stems and leaves is highly variable, ranging from glabrous to densely hairy. Pink flowers arranged on a dense, terminal spike up to 5 in long. Reproduces primarily by creeping rhizomes.
Key ID traits: Creeping rootstocks; long, lanceolate leaves with ochrea at the nodes. Pubescent stems and leaves.
Similar species: There are many similar species, all referred to as swamp smartweed. General growth habit is similar to Pennsylvania smartweed and ladysthumb, but swamp smartweed is typically found in wetter soils and reproduces primarily by the perennial rootstock. Former name was Polygonum amphibium.
Miscellaneous: In western Iowa swamp smartweed is known as tanweed due to coloration caused by the dense pubescence. Another common name for the plant is devil’s shoestring, referring to the long rhizomes.
- Retired Weed Scientist and Professor of Agronomy
- Field Agronomist in Central Iowa