Polygonum cespitosum Blume
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Freely branched, soon decumbent annual to 1 m, glabrous or partly strigose; lvs thin, dark green, lanceolate to elliptic or oblanceolate; ocreae strigulose or glabrous, ciliate with bristles 5–10 mm, racemes dense, 2–4 cm × 5 mm; ocreolae overlapping, their cilia mostly 2–3.5 mm, often equaling or surpassing the fls; achenes black, smooth and shining, trigonous, 2–2.5 mm; 2n=22, 24. Native of e. Asia, now a common weed, especially in moist soil, in much of our range, especially eastward. (Persicaria longiseta) Most of or all our plants represent the var. longisetum (De Bruyn) Stewart. Var. cespitosum, with shorter bristles on the ocreae and ocreolae, may also be expected.