Polygonum hydropiperoides is a perennial herb to 1 m; colonial by slender, tough, branching, creeping rhizomes; stems somewhat reclining; leaf sheath membranous, appressed brownish hairy, top fringed with long bristles.
Leaves alternate, narrow.
Flowers pink to white, radially symmetrical; 5 petals (tepals), basal bracts tubular, appressed bristly, usually not overlapping, in erect, slender terminal or axillary racemes 2-8 cm long, raceme stalks appressed bristly above; blooming and fruiting July-Nov. (Hough 1983).
Fruit dry, achenes trigonous, smooth, shiny, rounded angles, concave sides, to 0.3 cm long, 0.2 cm cm wide.
Wetland status: OBL.
Frequency in NYC: Infrequent.
Habitat: Open wet soil, pond edges.