Elodea nuttallii (Planch.) H.St.John
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Habitally like no. 1 [Elodea canadensis Michx.], but the lvs narrower, paler, and softer, mostly 0.3–1.75 (avg 1.3) mm wide, not imbricate at the stem-tip; staminate spathes sessile, broadly ovoid 2–4 mm, the sessile staminate fl breaking loose and floating to the surface at anthesis, its sep 2 mm, the pet wanting or minute (to 1.5 mm); pistillate fls with sep 1–2 mm and pet 1–2(–2.5) mm; 2n=48. In quiet, usually noncalcareous water; Me. and Que. to Minn. and Nebr., s. to N.C., Miss., and Mo., and irregularly in w. U.S. July–Sept. (Anacharis n.; A. occidentalis; Philotria angustifolia; P. minor)