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. The two types differ as follows:
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.
Duration: Perennial Nativity: Non-Native Lifeform: Forb/Herb General: Perennial aquatic or semi-aquatic herb; succulent stems floating, creeping or ascending, rooting at the nodes, 10-80 cm or more long; glabrous. Leaves: Pinnately divided into ovate to orbicular segments, the terminal one the largest, 1-10 cm long, narrowly clasping at the base. Flowers: Racemes without bracts; pedicels spreading to ascending, 5-13 mm long; sepals 2-3 mm long, green or with white tips; petals white, 3-5 mm long, oblanceolate. Fruits: Siliques spreading or curved upward, 1-3 cm long, 2-3 mm wide; style about 1 mm long. Ecology: Found in water or very wet soil; 1,500-7,500 ft (460-2285 m); flowers April-August. Distribution: Introduced to all of N. America, found in every state in the US; south through MEX, C. America and S. America; throughout much of the rest of the world on every continent. Notes: Highly distinct and ubiquitous plant of wetlands; distinguished by the fact it is only in wet places; has creeping, highly branched stems which cover areas, root at nodes and float in water; pinnately compound leaves; inflorescences of white petals and elongated fruits. Greens have a spicy mustard taste. Ethnobotany: Havasupai used for food. Other tribes and cultures around the world eat as greens. Sold in some supermarkets. Etymology: Rorippa is an Anglo-Saxon work rorippen with an uncertain meaning, while nasturtium-aquaticum is from the Latin nasus tortus, a twisted nose. Synonyms: Rorippa nasturtium-aquaticum, Sisymbrium nasturtium-aquaticum, Nasturtium nasturtium-aquaticum Editor: SBuckley 2010, FSCoburn 2015