Epilobium angustifolium Linnaeus subsp. circumvagum Mosquin, Brittonia 18: 169. 1966, based on Chamaenerion angustifolium var. platyphyllum Daniels, Univ. Missouri Stud., Sci. Ser. 2: 176. 1911; C. angustifolium var. abbreviatum Lunell; C. angustifolium var. canescens (Alph. Wood) Britton; C. angustifolium subsp. macrophyllum (Haussknecht) Czerepanov; C. danielsii (D. Löve) Czerepanov; C. exaltatum Rydberg; Chamerion angustifolium (Linnaeus) Holub var. canescens (Alph. Wood) N. H. Holmgren & P. K. Holmgren; C. angustifolium subsp. circumvagum (Mosquin) Hoch; C. danielsii (D. Löve) Czerepanov; C. platyphyllum (Daniels) Á. Löve & D. Löve; E. angustifolium var. abbreviatum (Lunell) Munz; E. angustifolium var. canescens Alph. Wood; E. angustifolium subsp. macrophyllum (Haussknecht) Hultén; E. angustifolium var. macrophyllum (Haussknecht) Fernald; E. angustifolium var. platyphyllum (Daniels) Fernald; E. danielsii D. Löve; Pyrogennema angustifolium (Linnaeus) Lunell var. abbreviatum (Lunell) Lunell

Stems 30–200 cm, sparsely strigillose, usually glabrous proximally. Leaves: petioles 2–7 mm; cauline blades oblong- to elliptic-lanceolate, (6–)9–23 × (0.7–)1.5–3.4 cm, base subcuneate to attenuate, margins ± denticulate, surface strigillose on adaxial side and on abaxial midrib, or, rarely, glabrous. Inflorescences strigillose; bracts 7–25 mm. Flowers: sepals 9–19 × 1.5–3 mm, acuminate; petals obovate to suborbicular, 14–25 × 7–14 mm, entire or scarcely emarginate; filaments 8–17 mm; anthers 2.5–3 mm; pollen mixed 3- and 4-porate (rarely 5-porate), 70–95 µm diam.; ovaries 8–25 mm, style 9–18 mm. Capsules 5–9.5 cm; pedicels 1–3 cm. Seeds 1–1.3 × 0.3–0.4 mm. 2n = 72, 108.

Flowering Jun–Sep. Moist, often disturbed places in montane and boreal forest regions, frequent after fires; 0–3800 m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld. and Labr., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Ariz., Ark., Calif., Colo., Conn., Del., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Tenn., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; Mexico (Coahuila, Nuevo León); Eurasia.