Description from Flora of China
Persicaria dichotoma (Blume) Masamune; P. peduncularis (Wallich ex Meisner) Nemoto; Polygonum pedunculare Wallich ex Meisner; P. strigosum R. Brown var. pedunculare (Wallich ex Meisner) Steward; P. tetragonum Blume; Tracaulon pedunculare (Wallich ex Meisner) Greene; T. tetragonum (Blume) Greene; Truellum dichotomum (Blume) Soják.
Herbs annual (?perennial). Stems ascending or erect, 40-100 cm tall, often branched, with sparse retrorse prickles. Petiole 5-10 mm; leaf blade lanceolate or narrowly elliptic, 5-10 × 1-3 mm, both surfaces glabrous, abaxially with retrorse prickly midvein, base cuneate, truncate, or subhastate, margin entire, not ciliate or very shortly ciliate, apex acute; ocrea tubular, 1.5-2 cm, membranous, usually glabrous, apex oblique, not ciliate. Inflorescence terminal or axillary, densely shortly spicate, usually 1 or 2 × dichotomously branched; peduncle glandular hairy; bracts broadly elliptic, 2-3 mm, ciliate, each 2- or 3-flowered. Pedicels shorter than bracts. Perianth pinkish, 5-parted; tepals broadly elliptic, 2-3 mm. Stamens 5, included. Styles 2, free; stigmas capitate. Achenes included in persistent perianth, brown, dull, nearly orbicular, biconvex, 2-2.5 mm. Fl. Jun-Jul, fr. Aug-Oct.
One of us (Park) notes that this is an extremely variable species, and consists of two varieties, Polygonum dichotomum var. dichotomum and var. angustissimum (J. D. Hooker) C. W. Park (see Park, Mem. New York Bot. Gard. 47: 75. 1988), but only the typical variety occurs in China.
Ditches, marshy areas; 100-1000 m. Fujian, Guangdong, ?Guangxi, Hainan, ?Hubei, Taiwan [India (Assam), Indonesia, Japan (Ryukyu Islands), Laos, Malaysia, Philippines, Thailand, Vietnam; Australia].