Aquatic and Wetland Vascular Plants of the Northern Great Plains
15. Polygonaceae, the Smartweed Family
1. Polygonum L. -- Smartweed, knotweed, tear-thumb5. Polygonum hydropiperoides Michx.-- Mild water pepper
Erect to decumbent, usually branched perennial, nearly glabrous to strigose throughout; stems commonly rooting at the lower nodes when decumbent, to 1 m long. Leaf blades linear-lanceolate to lanceolate, 4-12 cm long, 0.3-2.5 cm wide, nearly glabrous to strigose, especially pubescent on the midvein and margins, gradually tapering to a narrow, blunt to acute tip, cuneate at the base, short-petioled to subsessile; ocreae membranous, 5-15 mm long, usually strigose, fringed with bristles. Racemes 2-several, slender, often interrupted in the lower portion, 1-6 cm long. Flowers greenish to white or pinkish; calyx 2-3 mm long, 5-parted to just below the middle, eglandular or only the inner sepals slightly glandular; stamens 8, included; style branches 3. Achenes black, shiny, trigonous with concave sides, 2-3 mm long. Aug--Sep. Wet soil or mud of meadows, marshes, ditches, stream banks and shores; uncommon and scattered; (Que. to B.C., s through the U.S. and into C. and S.Amer.).
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