- Scientific Name: Reynoutria japonica Houttuyn
- Ref: Nat. Hist. 2(8): 639. 1777.
- Synonym: Fallopia japonica (Houttuyn) Ronse Decraene; F. japonica var. compacta (J. D. Hooker) J. Bailey; Pleuropterus cuspidatus H. Gross; Polygonum cuspidatum Siebold & Zuccarini (1846), not Willdenow ex Sprengel (1825); Reynoutria henryi Nakai; Tiniaria japonica (Houttuyn) Hedberg.
- English Common Name: Asian knotweed, Japanese knotweed
- Chinese Common Name: 虎杖 hǔzhàng
- Japanese Common Name: イタドリ [疼取/痛取] itadori
- Family: Polygonaceae
- Genus: Reynoutria
- Distribution: Thickets in valleys, field margins, mountain slopes; 100-2000 m. Anhui, Fujian, N Gansu, Guangdong, Guangxi, Guizhou, Hainan, ?Heilongjiang, Henan, Hubei, Hunan, Jiangsu, Jiangxi, ?Liaoning, N Shaanxi, Shandong, Sichuan, Taiwan, Yunnan, Zhejiang [Japan, Korea, Russia (Far East); widely cultivated and becoming a weed in other parts of the world].
- Photo: 08/26/2017, Yunhe, Zhejiang
Herbs perennial. Rhizomes thickened. Stems numerous, erect, 1-2 m tall, stout, branched above, striate, papillate, often with red or purple spots. Leaves often deciduous; petiole 1-2 cm, papillate; leaf blade ovate or broadly elliptic, 5-12 × 4-9 cm, subleathery, both surfaces glabrous, papillate along veins, base broadly cuneate, rounded, or truncate, margin entire, apex acute or shortly acuminate, not ciliate. Inflorescence axillary, paniculate, 3-8 cm; bracts funnel-shaped, 1-2 mm, oblique, each 2-4-flowered. Pedicels 3-4 mm, slender, articulate below middle. Perianth white or greenish, 5-parted. Male flowers: stamens 8, longer than perianth. Female flowers: 3 outer tepals accrescent and winged on abaxial surface; styles 3; stigmas fimbriate. Achenes included in persistent perianth, black-brown, shiny, ovoid-ellipsoid, 4-5 mm. Fl. Jun-Sep, fr. Jul-Oct. 2n = 44, 52*.(Flora of China)
