Isoëtes lacustris

Lvs mostly 5-10(-20) cm נ0.7-2 mm, erect to often recurved, relatively coarse and firm, carrying their width well toward the acute tip, fleshy and brittle, twisted, dark green, generally lacking both stomates and peripheral strands; sporangia 3-5 mm, pale, only rarely spotted, to one-half covered by the velum; megaspores mostly 0.5-0.8 (avg >0.6) mm wide, beset with jagged crests or high ridges that may form an irregular reticulum, varying to rarely (I. hieroglyphica) with a loose reticulum of low rounded ridges or with scattered low mounds; 2n=110. Submersed (0.5-)1-3+ m in cold ponds, lakes, or streams, rooted in gravel; circumboreal, s. to N.J., Mich., Wis., Minn., and Colo.; disjunct in the mts. of Va. and Tenn. (I. macrospora)

Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.

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