Epilobium arcuatum H. Léveillé; E. axillare Franchet ex Koidzumi; E. chrysocoma H. Léveillé; E. hakkodense H. Léveillé; E. japonicum (Miquel) Haussknecht; E. japonicum var. glandulosopubescens Haussknecht; E. kiusianum Nakai; E. makinoense H. Léveillé; E. myokense Koidzumi; E. nakaianum H. Léveillé; E. oligodontum Haussknecht; E. prostratum H. Léveillé (1907), not Warburg (1893); E. pyrricholophum var. anuoleucholophum H. Léveillé; E. pyrricholophum var. curvatopilosum H. Hara; E. pyrricholophum var. japonicum (Miquel) H. Hara; E. pyrricholophum f. kiusianum (Nakai) Nakai; E. quadrangulum H. Léveillé; E. rouyanum H. Léveillé; E. tetragonum Linnaeus var. japonicum Miquel.

Herbs perennial, erect, with basal filiform stolons with small widely spaced leaves. Stems 25-80 cm tall, usually well-branched or simple, strigillose and glandular pubescent throughut, especially dense on inflorescence. Leaves crowded, subsessile; cauline blade ovate to broadly oblong, upper ones narrowly ovate to lanceolate, 2-6 × 0.5-2 cm, both surfaces strigillose especially on margin and veins, base obtuse to subcordate, margin usually sharply serrulate with 7-15 teeth per side, apex acute or subobtuse. Inflorescence and flowers erect. Sepals 4-7 mm. Petals pink to purple, 6-8 mm. Stigma clavate to subcapitate, entire. Capsules 3.5-7.5 cm, strigillose, glandular; pedicels 0.7-1.5 cm. Seeds brown, 1.5-1.8 mm, finely papillose, with conspicuous chalazal collar 0.08-0.1 mm; coma reddish brown, rather persistent. Fl. Jul-Sep, fr. Aug-Nov. 2n = 36.

Wet places along streams and low areas, disturbed moist hillsides in mountains; (100-)300-1800 m. Anhui, Fujian, Guangdong, Guangxi, Guizhou, Henan, Hubei, Hunan, Jiangsu, Jiangxi, Shaanxi, Shandong, E Sichuan, Zhejiang [Japan, Russia (Far East)].