Lvs more slender, the middle cauline ones 180-500 times as long as wide, mostly 0.1-0.35 (avg 0.2) mm wide; floating lvs 3-7-veined, to 11 mm wide; northeastern, mainly from Me. to N.J. and Pa., w. irregularly to s. Ont., Mich., n. Ind., Wis., and c. Minn. (P. bicupulatus; P. capillaceus, misapplied)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.