Water Horsetail

Appearance

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.

Naming

Equisetum fluviatile Linnaeus
Equisetum limosum Linnaeus

Distribution

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

Behavior

Colonies of Water Horsetail help to provide cover for various invertebrate and vertebrate animals, including wetland birds. Dragonflies sometimes use the apices of stems and cones as perching sites.

Habitat

Standing in water, in ponds, ditches, marshes, swales

Reproduction

By spores and rhizomes. Spore cones maturing in summer.

Predators

Various monophagous or oligophagous insects are known to feed on horsetails (Equisetum spp.). These species include the larvae of leaf-mining flies (some Liriomyza spp.), leaf beetles (Hippuriphila spp.), larvae of sawflies (some Dolerus spp.), Grypus equiseti (Horsetail Weevil), and Anoecia equiseti (an aphid). In North America, most of these species have been observed to feed on Field Horsetail (Equisetum arvense), while similar species in Europe have been observed to feed on Water Horsetail (Equisetum fluviatile) and other horsetails; see Poinar (2014) for more information. Among vertebrate animals, the stems of horsetails are eaten by the American Moose and Muskrat (Martin et al., 1951/1961).