Aerial stems having basal part persisting over winter, unbranched, 20--180 cm; lines of stomates single; ridges 14--32. Sheaths elongate, 7--17 × 3--12 mm, becoming dark-girdled with age; teeth 14--32, articulate and promptly shed or persistent. Cone apex pointed; spores white, misshapen. Cones maturing in late spring--early summer but spores not shed. Moist lakeshores, riverbanks, roadsides, prairies; 0--2500 m; Alta., B.C., Ont., Que., Sask.; Ariz., Ark., Calif., Colo., Conn., Del., D.C., Idaho, Ill., Ind., Iowa, Kans., Maine, Md., Mass., Mich., Minn., Mo., Mont., Nebr., Nev., N.H., N.J., N.Mex., N.Y., N.C., N.Dak., Ohio, Okla., Oreg., Pa., R.I., S.Dak., Tex., Utah, Vt., Va., Wash., W.Va., Wis., Wyo.; n Mexico including Baja California. The hybrid between Equisetum hyemale and E . laevigatum , E . × ferrissii , was mistaken for E . laevigatum by Schaffner and some subsequent authors. Although sterile, it exists outside the range of E . laevigatum , and apparently it is dispersed vegetatively (R.L. Hauke 1963). Perhaps it has persisted in some areas from a time when the parents were both there. Equisetum × ferrissii has been reported from Maine, New Hampshire, Rhode Island, South Dakota, and Vermont, but I have not seen specimens from those states.

General: Hybrid between E. hyemale and E. laevigatum. Monomorphic stems, evergreen 30-200 cm tall. Leaves: Erect, 14-50 ridged, erect, the surface roughened, usually dark green at maturity, unbranched or with irregular, scattered branches were wounded, these with 6-20 ridges; sheaths as long or slightly shorter than wide, marked with dark basal band, light gray to brown central band, and a dark tip, teeth 14-50 per sheath, 2-4 mm long, gray to black. Sporangia: Sterile hybrid, but bearing a false strobili with a somewhat mucronate tip. Ecology: Found in moist soil along stream banks and rivers, and marshy meadows from 2,500-8,500 ft (762-2591 m). Notes: Distinguished by looking at the sterile strobili, which when broken open will reveal a cottony mass of elaters, but not mature green, globose spores. Ethnobotany: Similar uses to other species in the genera. Etymology: Equisetum is from equus, horse and seta, bristle, while ferrissii is named for James Henry Ferriss (1849-1926) an American collector of land-snails, fossils, ferns, and cacti throughout the West. Sources: Yatskievych and Windham 2008