Aerial stems monomorphic, green, unbranched or branched, 35--115 cm; hollow center large, to 9/10 stem diam.; vallecular canals absent. Sheaths squarish in face view, ca. 4--10 × 4--10 mm; teeth black, occasionally with narrow white border, 12--24, narrow, 2--3 mm. Branches when present only from midstem nodes, spreading, hollow, ridges 4--6, valleys rounded; 1st internode of each branch shorter than subtending stem sheath; sheath teeth narrow. 2 n =216. Cones maturing in summer. Standing in water, in ponds, ditches, marshes, swales; 0--1500 m; St. Pierre and Miquelon; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska including the Aleutian Islands, Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Maine, Md., Mass., Mich., Minn., Mont., Nebr., N.H., N.J., N.Y., N.Dak., Ohio, Oreg., Pa., R.I., S.Dak., Vt., Va., Wash., W.Va., Wis., Wyo.; Eurasia s to n Italy, China, Korea, Japan.

Stems annual, all alike, to 1 m or more, shallowly 9-25-ridged, the ridges smooth or nearly so, the stomates in a single broad band in each furrow; central cavity commonly more than ޠthe diameter of the stem, the vallecular cavities commonly lacking except near the base; sheaths green, 4-9 mm, with persistent, narrow, sharp, black or blackish teeth 1.5-3+ mm, these not or scarcely hyaline- margined; branches none to often numerous and whorled at the middle and upper nodes, 4-6-angled, simple, the first internode slightly shorter than the associated stem-sheath; cone pedunculate, 1-2 cm, deciduous. In shallow water, along muddy shores, and in marshes and bogs; circumboreal, in Amer. s. to Pa., Ill., Io., Nebr., and Wash.

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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