2.
Equisetum palustre
Linnaeus, Sp. Pl. 2: 1061. 1753.
Marsh horsetail, prêle des marais
Equisetum palustre
var.
americanum
Victorin
Aerial stems monomorphic, green, branched or unbranched, 20--80 cm; hollow center small, to 1/3 stem diam.; vallecular canals nearly as large. Sheaths elongate, 4--9 × 2--5 mm; teeth dark, 5--10, narrow, 2--5 mm, margins white, scarious. 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. Marshes and swamps; 0--1500m; Alta., B.C., Man., N.B., Nfld., N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon; Alaska, Calif., Idaho, Maine, Mich., Minn., Mont., N.H., N.Y., N.Dak., Oreg., Pa., Vt., Wash., Wis.; Eurasia s to Himalayas, n China, Korea, Japan.
The name Equisetum palustre var. americanum has been used for specimens from the flora that have longer teeth than those from Eurasia.
