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Northern Prairie Wildlife Research Center

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Aquatic and Wetland Vascular Plants of the Northern Great Plains

15. Polygonaceae, the Smartweed Family

1. Polygonum L. -- Smartweed, knotweed, tear-thumb

11. Polygonum sagittatum L.-- Tear-thumb, arrow-vine

Slender annual; stems weak, usually reclining on surrounding vegetation, to 2 m long, strongly 4-angled, armed with reflexed prickles on the angles, the prickles usually continuous onto the petioles, leaf midribs and peduncles. Leaves mostly long-petioled below, becoming short-petioled upward on the stem, the blades lanceolate to elliptic and sagittate, 3-10 cm long, 0.8-2.5 cm wide, acute, the basal lobes straight or incurved; ocreae 5-10 mm long, sparsely ciliate. Racemes terminal and axillary on slender peduncles, globose, 5-10 mm long. Flowers whitish or pinkish; calyx 2.5-3 mm long, 5-parted to below the middle; stamens 8, included; style branches 3. Achenes brown to black, shiny, trigonous, 2-3 mm long. Jul--Sep. Swamps, springs and wet meadows; rare in ND and SD, frequent in NE Sand Hills; (Newf. and Que. to Sask., s to FL and TX).
GIF- Distribution Map

Map key

Previous Species -- Polygonum ramosissimum Michx.-- Bushy knotweed
Return to Family -- Polygonaceae - The Smartweed Family
Next Species -- Rumex altissimus Wood -- Pale dock

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