Equisetum hyemale subsp. affine
Aerial stems persisting more than a year, unbranched, 18–220 cm; lines of stomates single; ridges 14–50. Sheaths when mature dark-girdled, brown to gray above girdle, squarish in face view, 4.5–17 × 3.5–18 mm; teeth 14–50, articulate and promptly shed or persistent. Cone apex pointed; spores green, spheric. 2n =216.
Phenology: Cones maturing in summer, old stems sometimes developing branches with cones in spring.
Habitat: Moist roadsides, riverbanks, lakeshores, woodlands
Elevation: 0–3000 m
Alta., B.C., Man., N.B., Nfld. and Labr. (Nfld.), N.W.T., N.S., Ont., P.E.I., Que., Sask., Yukon, Ala., Alaska including the Aleutian Islands, Ariz., Ark., Calif., Colo., Conn., Del., D.C., Fla., Ga., Idaho, Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.C., S.Dak., Tenn., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo., Mexico, Central America in Guatemala.
In southern and central to western regions plants tend to be taller and have more persistent teeth (Equisetum robustum, E. prealtum); in the Far West they often have bituberculate ridges (E. hyemale var. californicum). Equisetum hyemale subsp. hyemale is found in Europe and Asia to northwestern China in Xinjiang.