Description from Flora of China
Polygonum pensylvanicum Bunge, Enum. Pl. China Bor. 57. 1833, not Linnaeus (1753); Persicaria bungeana (Turczaninow) Nakai ex T. Mori; Polygonum chanetii H. Léveillé.
Herbs annual. Stems erect or ascending, 30-80 cm tall, branched, retrorsely prickly. Petiole 5-10 mm; leaf blade green adaxially, lanceolate or narrowly elliptic, 4-13 × 1-3 cm, abaxially hispidulous, adaxially glabrous, usually hispidulous along midvein, base cuneate, margin ciliate, apex acute or subacuminate; ocrea tubular, 1-1.5 cm, membranous, apex truncate, long ciliate. Inflorescence terminal or axillary, spicate, 5-10 mm, usually branched, interrupted at base; peduncle densely glandular hairy; bracts green, funnel-shaped, not ciliate, glabrous, often with few glandular hairs. Pedicels shorter than bracts. Perianth white or pinkish, 5-parted; tepals elliptic, 3-4 mm. Stamens 8, in 2 whorls, included. Styles 2, connate to below middle; stigmas capitate. Achenes included in persistent perianth, black, dull, orbicular, biconvex, ca. 3 mm. Fl. Jul-Aug, fr. Aug-Sep. 2n = 20.
Grassy valleys, near fields, roadsides; sea level to 1700 m. Gansu, Hebei, Heilongjiang, Jiangsu, Jilin, Liaoning, Nei Mongol, Ningxia, Shandong, Shanxi [Japan, Korea, Russia (Far East)].