1.
Equisetum fluviatile
Linnaeus, Sp. Pl. 2: 1062. 1753.
River horsetail, pipes, prêle fluviatile
Equisetum limosum
Linnaeus
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.
