Lvs mostly 5-20+ cm נ0.25-1.5 mm, erect to often recurved, thin, soft and flaccid, twisted or not, yellowish-green to bright green, with few or no stomates and without peripheral strands; sporangia 2-5 mm, pale or uniformly tan, seldom brown-spotted, to one-third covered by the velum; megaspores mostly 0.4-0.65 (avg <0.6) mm wide, commonly high- crested as in no. 7 [Iso쵥s lacustris L.], but varying to rarely (I. acadiensis) with a loose reticulum of low, rounded ridges; 2n=44. Rather shallowly (to 1 m) submersed in ponds or lakes, less often in rivers, rooted in gravel, sand, or mud, rarely amphibious; N.S. and P.E.I. to Que., s. to N.Y. and Md.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.