Much like no. 8 [Epilobium ciliatum Raf.], but the stem arising from a large, subterranean turion; pls often simple or only sparsely branched even when well developed; lvs avg wider, mostly ovate or narrowly ovate; infl tending to be leafy and narrow, not much branched; pet mostly (5-)6-10 mm, rose-purple to rarely white; seeds 1-1.5 mm, similarly ridged, or seldom merely papillate; 2n=36. Wet places, typically in cooler, more stable habitats than no. 8; Nf. to Alas. and Asia, s. to N.S., N.B., Vt., n. N.Y., n. Mich., Wis., Minn., and in the w. to N.M. and Calif. June-Aug. (E. boreale; E. leptocarpum; E. steckerianum; E. ciliatum var. g.) Hybridizes with no. 8.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.