Aquatic and Wetland Vascular Plants of the Northern Great Plains
15. Polygonaceae, the Smartweed Family
1. Polygonum L. -- Smartweed, knotweed, tear-thumb6. Polygonum lapathifolium L.-- Pale smartweed
Erect to decumbent, simple to widely branching annual (1)2-10 dm tall. Leaf blades lanceolate or elliptic-lanceolate, 4-17(20) cm long, 0.5-3.5(5) cm wide, glabrous above, glabrous to minutely strigose and often glandular-punctate beneath, occasionally finely white-tomentose beneath, acute or acuminate to the narrow, blunt tip, cuneate at the base, on short petioles to 2 cm long; ocreae 5-20 mm long, entire to lacerate, glabrous, not fringed with bristles. Racemes usually numerous, densely flowered, cylindric, erect or often nodding, 0.8-5 cm long, 0.5-1 cm thick. Flowers greenish-white or white to deep pink; calyx 2.5-3.5 mm long, 4- or 5-lobed to below the middle, the outer 2 sepals strongly 3-nerved, each nerve ending in an anchor-shaped fork; stamens usually 6, included; style branches 2. Achenes brown to dark brown, lenticular, concave on the sides, ca. 2 mm long, including the style beak. Jul--Sep. Marshes, wet meadows, ditches, shores, stream banks and other places where water stands temporarily; very common, often abundant; (Circumboreal, s throughout most of the U.S.).
Polygonum lapathifolium. The spikelike racemes are usually erect and shorter on smaller plants. The flowers can be strongly pink. |
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