Description from Flora of China
Persicaria glabra (Willdenow) M. Gomez; Polygonum densiflorum Meisner; P. portoricense Bertoloni ex Endlicher.
Herbs annual, glabrous throughout. Stems erect, 70-100 cm tall, dilated at nodes, rarely branched. Petiole 8-10 mm, robust; leaf blade lanceolate or oblong-lanceolate, 8-18 × 1.5-3 cm, base narrowly cuneate, margin entire, not ciliate, apex narrowly acuminate; ocrea tubular, 1-3 cm, membranous, veins numerous. Inflorescence terminal, spicate, 4-12 cm, usually with several dense spikes aggregated and panicle-like; bracts funnel-shaped, not ciliate, usually each 3- or 4-flowered. Pedicel large, longer than bracts, articulate at apex. Perianth white or pinkish, 5-parted; tepals elliptic, 3-4 mm, veins slender, furcate at apex, not curved downward. Stamens 6-8. Styles 2, connate to below middle. Achenes included in persistent perianth, black-brown, shiny, ovoid, biconvex, 2.5-3 mm. Fl. Jun-Aug, fr. Jul-Sep.
Riverbanks, streamsides, marshy areas; sea level to 100 m. Fujian, Guangdong, Guangxi, Hainan, Hubei, Hunan, Taiwan [Bangladesh, Bhutan, India, Myanmar, Philippines, Sri Lanka, Thailand, Vietnam; Africa, Australia, North and South America, Pacific Islands].