Aerial stems dimorphic; vegetative stems green, branched, 16--50 cm; hollow center 1/6--1/3 stem diam. Sheaths somewhat elongate, 3--5 × 2--4 mm; teeth 8--18, narrow, 1.5--4 mm, centers dark and margins white. Branches in regular whorls, horizontal to drooping, solid; ridges 3; valleys channeled; 1st internode of each branch equal to or longer than subtending stem sheath; sheath teeth deltate. Fertile stems brown, with stomates, initially unbranched, persisting and becoming branched and green after spore discharge. Cones maturing in late spring. Meadows, wet woodlands; 0--2000 m; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Conn., Ill., Iowa, Maine, Mass., Mich., Minn., N.H., N.Y., N.Dak., Vt., Wis.; n Eurasia to ne China, Japan in Hokkaido.
Stems annual, dimorphic, the sterile ones 2-5 dm, 1-3 mm thick, smoothish toward the base, otherwise beset with high, blunt, siliceous tubercles or very short, high, transverse ridge-crests on the (6-)10-18 ridges, with rather small vallecular cavities and a fairly large central cavity commonly 1/3-1/2 the diameter of the stem, the stomates in 2 broad bands in each furrow; sheaths 2-6 cm, green, the teeth 1-2 mm, persistent, only basally connate, with pale, hyaline margins and a firmer dark midstripe; branches regularly whorled at the middle and upper nodes, solid, mostly 3-angled, simple, the first internode to as long as the associated stem-sheath; fertile stems with simple branches, otherwise as in E. sylvaticum. Streambanks and moist woods; circumboreal, s. in our range to N.J. and ne. Io.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.