Aquatic and Wetland Vascular Plants of the Northern Great Plains
15. Polygonaceae, the Smartweed Family
1. Polygonum L. -- Smartweed, knotweed, tear-thumb7. Polygonum pensylvanicum L.-- Pennsylvania smartweed
Erect, simple to widely branching annual 3-12 dm tall. Leaf blades ovate-lanceolate to lanceolate, 3-15 cm long, 0.7-4 cm wide, glabrous except for the minutely strigose margin, sometimes puncticulate on the lower surface, acute or acuminate to the narrow, blunt tip, cuneate at the base; petioles short to 2.5 cm long; ocreae 0.5-1.5 cm long, entire to lacerate, glabrous, not fringed with bristles. Racemes usually few to many, dense, cylindric, erect, 1-3 cm long, 0.7-1 cm thick; peduncles glandular-pubescent. Flowers pink to nearly white; calyx 3-4.5 mm long, 5-lobed to well below the middle, the outer sepals with faint, irregularly forked nerves; stamens 8 or fewer, included; style branches 2. Achenes dark brown to black, shiny, lenticular, concave on the sides, 2.5-3 mm long, including the beak. Jul--Aug. Stream banks, shores and ditches; occasional to common; e ND, e and c SD and NE; (N.S. and Que. to ND, s to FL, TX and AZ).
Previous Species -- Polygonum lapathifolium L.-- Pale smartweed
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