Rhizome 0.3-1.5 cm thick; lvs usually submerged, very thin, linear, 15-100 cm נ2-13 mm, but sometimes terrestrial or emersed, the blade then rather narrowly lance-elliptic, tapering to the base, 2-6 cm נ4-15 mm, 2.7-5 times as long as wide; pedicels stout; sep 1.3-2.2 mm; pet faintly anthocyanic, 2.3-3.7 נ2.1-3.7 mm; anthers 0.3-0.6 mm; style short, 0.3-0.6 mm, uncinate-curved; achenes 11-20, 1.8-2.6 mm, with a median dorsal ridge flanked by a groove on each side; 2n=14. Circumboreal, in Amer. s. to N.Y., Wis., Mo., Nebr., Colo., and Calif. June-Aug. (A. geyeri)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.