Aerial stems lasting less than a year, occasionally overwintering in the southwestern United States, usually unbranched, 20--150 cm; lines of stomates single; ridges 10--32. Sheaths green, elongate, 7--15 × 3--9 mm; teeth 10--32, articulate and usually shed early, leaving dark rim on sheath. Cone apex rounded to apiculate with blunt tip; spores green, spheric. 2 n =216. Cones maturing in spring--early summer. Moist prairies, riverbanks, roadsides; 1530--3500 m; Alta., B.C., Man., Ont., Que., Sask.; Ariz., Ark., Calif., Colo., Idaho, Ill., Ind., Iowa, Kans., Mich., Minn., Mo., Mont., Nebr., Nev., N.Mex., N.Dak., Ohio, Okla., Oreg., S.Dak., Tex., Utah, Wash., Wis., Wyo.; n Mexico including Baja California. Schaffner named this species Equisetum kansanum because he applied the name E . laevigatum to what we now know is the hybrid E . × ferrissii . The coarser-stemmed, occasionally persistent forms in the southwestern United States have been called Equisetum funstonii .

Stems all alike, annual (reputedly sometimes perennial toward the southwest), mostly unbranched, 3-10 dm, 3-8 mm thick, with mostly (10-)16-32 ridges, these smooth or commonly with inconspicuous, low, transverse wrinkle-ridges; central cavity mostly 2/3-3/4 the diameter of the stem, much larger than the small vallecular ones; stomates in 2 lines in each furrow; sheaths mostly 7-15 mm, mainly green, black-banded at the apex only, or the lowest ones sometimes black also at the base or throughout, the dark, scarious-margined teeth promptly and regularly deciduous; cones short-pedunculate, 1-2.5 cm, blunt or often inconspicuously short-apiculate. Open wet places; s. B.C. to Baja Calif., e. to s. Ont., w. N.Y., O., w. Va., Ill., Okla., and Tex. (E. kansanum)

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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