Rorippa nasturtium-aquaticum (L.) Hayek
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Species Description - Perennial; stems submersed or partly floating, or prostrate on mud, freely rooting; lvs of 3–9 obtuse segments, the lateral ovate to rotund, the terminal much larger, usually rotund; fls 5 mm wide, the pet twice as long as the sep; mature pedicels divaricate, 8–15 mm; frs slender, 1–2.5 cm, the beak 1 mm; seeds coarsely reticulate; 2n=32, 48, 64. Native of Eurasia, now widely established in clear quiet water throughout the U.S. and s. Can. All summer. (Radicula n.; Sisymbrium n.; Nasturtium microphyllum; N. officinale) Some botanists now restrict the name R. nasturtium-aquaticum to the "diploid" race (2n=32), and call the tetraploids (2n=64) R. microphylla (Boenn.) Hyl., regarding the plants with 2n=48 as vegetatively reproducing hybrids.