Hydrilla verticillata (L.f.) Royle
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Plants producing small tubers; lvs up to 20(–40) × 2(–5) mm, denticulate; stipules fringed with orange-brown hairs; staminate fls breaking loose as in Elodea nuttallii; sep 1.5–3 mm; pet narrower, transparent, with a few red streaks; 2n=16 (diploid), 24 (triploid). Rivers, lakes, and ponds; intr. in se. U.S. and spreading n. near the coast to Va., Md., D.C., and Del., locally abundant. June–Aug.