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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

1. Polygonum amphibium L. -- Water smartweed

Aquatic, amphibious or terrestrial perennial, quite variable depending on the water regime, glabrous when aquatic, commonly with spreading to appressed pubescence when terrestrial, more often flowering when in water. Stems trailing through water or over mud, usually branched, with the tips erect and emersed, to 1 m long, freely rooting at the nodes, or in drier situations, the stems erect from an underground portion, usually simple, to 8 dm tall. Leaves of submersed plants commonly floating, with leathery, glabrous blades on petioles 1-8 cm long; leaves of emersed plants often pubescent, sessile or with petioles to 5 mm long; leaf blades elliptic, elliptic-oblong or elliptic-lanceolate, 4-12(18) cm long, 1-4 cm wide, acute to obtuse or rounded at the tip, subcordate to cuneate at the base; ocreae membranous, 0.5-2 cm long, truncate at the summit or often with a spreading herbaceous margin on emersed plants, glabrous to strigose-hispid. Racemes terminal, 1-2, rarely 3 or 4, globose to short-cylindric, 1-3.5(5) cm long, 1-1.5(2) cm thick; peduncles 1.5-6 cm long, glabrous or pubescent, seldom glandular. Flowers rose pink; calyx 5-lobed to below the middle, 4-6 mm long; stamens 5, included or exserted; style branches 2. Achenes brown to nearly black, lenticular, 1.9-2.5 mm long. Jul--Sep. Meadows, marshes, springs, fens, streams, ponds and lakes, usually where water is fresh; occasional; (Nearly cosmopolitan). P. natans Eat.

P. amphibium as described here is considered in the strict sense. See the comments under P. coccineum.
GIF-Polygonum amphibium GIF- Distribution Map

Map key

Return to Family -- Polygonaceae - The Smartweed Family
Next Species -- Polygonum bicorne Raf.-- Pink smartweed

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