Much like no. 2 [Epilobium hirsutum L.], but smaller, to 8 dm, the lvs 2-8 cm, sessile or subsessile but not clasping, the upper commonly alternate; pet 4-9 mm, deeply notched. European sp., intr. into wet places in Mich. and s. Ont. July-Sept.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.