Description from Flora of China
Boisduvalia Spach; Chamaenerion Séguier; Zauschneria Presl.
Herbs perennial [or annual, sometimes suffrutescent], with leafy rosettes, stolons, soboles (shoots), or turions (subterranean globose buds with fleshy scales). Stems glabrous to pubescent, often with lines of hairs decurrent from margins of petioles. Leaves opposite, becoming alternate and bractlike in inflorescence; petiolate or sessile; stipules absent; bracteoles absent. Inflorescences simple or branched racemes, panicles, spikes, or corymbs. Flowers 4-merous, often protandrous, with floral tube, producing nectar at base of style. Petals pink to rose-purple or white [or rarely cream-colored or orange-red], obcordate or obtrullate, notched at apex. Stamens 8, in two unequal whorls; pollen yellow, shed in tetrads. Style erect; stigma entire or 4-lobed. Fruit an elongate, slender capsule, 4-loculed, loculidical. Seeds many [or rarely only 4], generally with terminal coma of silky hairs [or coma rarely lacking]. 2n = [18, 20, 24, 26, 28, 30, 32,] 36, [38, 60].
The genus is divided into seven sections, all present in North America but only one, Epilobium sect. Epilobium, in China, where the species occur in most temperate to montane habitats except extreme deserts or warm, subtropical forests.
Careful gathering of ripe seeds and perennating structures, usually at or just below the ground surface, facilitate identification. The pattern of vestiture on stems, also extremely valuable for identification, is sometimes obscure on specimens collected very late in the growing season.
About 165 species: montane, boreal, and/or arctic regions of Africa, Asia, Australasia, Europe, and North and South America, from sea level to 5000 m, often in moist, disturbed places: 33 species (nine endemic) in China.
(Authors: Chen Jiarui (陈家瑞 Chen Chia-jui); Peter C. Hoch, Peter H. Raven)