Northern Prairie Wildlife Research Center
Erect or decumbent perennial herbs; stems jointed and solid at the nodes, hollow through the internodes, longitudinally ridged, silicaceous, somethimes evergreen, some spp. dimorphic with colorless fertile stems which appear before the green sterile ones, the fertile stems eventually turning greenish in some; branches, if present, whorled in a regular or irregular fashion, arising from inside the sheath bases, sometimes rebranched; ridges of the stem, sometimes roughened with spicules of silica deposit; rhizomes deeply buried, with adventitious roots. Leaves small and scalelike, often lacking chlorophyll, whorled and united at the base to form sheaths around the stem, the teeth of the sheaths (corresponding to the leaves) free or coherent by the margins in pairs or groups. Sporangia homosporous, borne in a terminal cone made up of whorled, peltate sporangiophores; spores spherical, with 4 spirally wound elaters. Gametophyte photosynthetic.
Perhaps only Equisetum fluviatile and E. palustre are truly wetland plants, since they are more or less restricted to permanently saturated substrates. The remaining 5 species occurring in our region are either tolerant of wide-ranging soil moisture conditions or require consistently damp substrates, and so all have been included to ensure the proper identification of any equiseta encountered in wet places.
Hauke, R. L. 1965. Preliminary reports on the flora of Wisconsin. No. 54. Equisetaceae -- horsetail family. Trans. Wisconsin Acad. Sci. 54:331-346.
|1||Aerial stems fertile, brownish except that occasionally the sheaths may be green, or very small green branches may be present.||Lead 2|
|1||Aerial stems fertile or sterile, green.||Lead 4|
|2||Teeth of the sheaths with a white margin; stem becoming branched with green branches.||E. pratense|
|2||Teeth of the sheaths brown to blackish; stem simple or branched.||Lead 3|
|3||Stem becoming branched with green branches; teeth of the sheaths coherent in a few groups, reddish-brown, the groups with rounded to broadly acute tips.||E. sylvaticum|
|3||Stem not branched, soon withering; teeth of the lower sheaths dark brown to blackish, mostly separate, with long-acuminate tips.||E. arvense|
|4||Central cavity very large in relation to the diameter of the stem (ca. 4/5 the stem diameter), the stem wall thin; small outermost cavities opposite the ridges of the stem, i.e., on the same radius.*||E. fluviatile|
|4||Central cavity large or small, stem wall usually relatively thick; outermost cavities alternate with the stem ridges, i.e., on a different radius (a third set of smaller cavities often between the central one and the outermost).||Lead 5|
|5||Stem not branched above the base or only irregularly so; branches erect or strongly ascending.||Lead 6|
|5||Stem regularly branched above the base, the branches often spreading.||Lead 7|
|6||Sheaths longer than broad, with a dark apical band.||E. laevigatum|
|6||Sheaths shorter or not much longer than broad, with both an apical and a basal dark band.||E. hyemale|
|7||Teeth of the main stem sheaths reddish-brown, coherent in a few groups, especially toward the base of the stem; branches themselves branching.||E. sylvaticum|
|7||Teeth of the main stems sheaths whitish to black, sometimes brown but not reddish, separate or coherent in pairs; branches rarely branched.||Lead 8|
|8||Central cavity of the main stem about the same size as the outermost cavities; sheaths on the first internode of the branches with 5 or more teeth.||E. palustre|
|8||Central cavity of the main stem usually definitely larger than the outermost cavities; sheaths on the first internodes of the branches with 3 or 4 teeth.||Lead 9|
|9||Ridges of the main stem with spicules of silica deposit, especially on the upper part of the upper internodes.||E. pratense|
|9||Ridges of the main stem usually roughened but lacking spicules of silica deposit.||E. arvense|