Aerial stems dimorphic; vegetative stems green, branched, 2--60(--100) cm; hollow center 1/3--2/3 stem diam. Sheaths squarish in face view, 2--5(--10) × 2--5(--9) mm; teeth dark, 4--14, narrow, 1--3.5 mm, often cohering in pairs. Branches in regular whorls, ascending, solid; ridges 3--4; valleys channeled; 1st internode of each branch longer than subtending stem sheath; sheath teeth attenuate. Fertile stems brown, lacking stomates, unbranched, shorter than vegetative stems, with larger sheaths, fleshy, ephemeral. 2 n =ca. 216.
Phenology
Cones maturing in early spring
Altitude range
0--3200 m
Distribution
GreenlandSt. Pierre and Miquelonall states except Fla.Eurasia s to Himalayasc ChinaKoreaJapan.USA La.USA Miss.USA S.C.Canada Alta.Canada B.C.Canada Man.Canada N.B.Canada Nfld.Canada N.W.T.Canada N.S.Canada Ont.Canada P.E.I.Canada Que.Canada Sask.Canada Yukon
Discussion
Among the many infraspecific taxa that have been named in this species, Equisetum arvense var. boreale Bongard has been most generally accepted and has been applied to plants with tall, erect stems with 3-ridged branches. Because both 3-ridged and 4-ridged branches may occur on a single stem, the variety boreale is not recognized here as distinct (R.L. Hauke 1966).
