AERIAL STEMS: monomorphic, evergreen, 30–220 cm long, 14–50-ridged, erect (to prostrate after flooding), the surface somewhat roughened (sand-papery), usually dark green at maturity, unbranched or with irregular, scattered branches in wound-forms, these with 6–20 ridges. SHEATHS: as long as or slightly shorter than wide, variously marked with a dark basal band, a light gray to brown central band, and a dark tip, sometimes more or less uniformly darkened; teeth 14–50 per sheath (6–20 on branches), 2–4 mm long, gray to black. STROBILI: 8–25 mm long, the tips sharply mucronate. SPORES: 35–70 μm in diameter. 2n = 216. 2 subspp. [often treated as vars.]; N. Amer., C. Amer., Eur., Asia. REFERENCES: G.Yatskievych and M.D. Windham , 2008, Vascular Plants of Arizona: Equisetaceae. CANOTIA 4 (2): 41–45.