Plants glabrous throughout or sparsely pubescent. Stems (1-)2-10(-18) dm. Cauline leaves: petiole not winged, base auriculate; blade (3-)5-9(-11)-foliolate, (1.5-)2.5-10 (-15) cm; lateral leaflets sessile or petiolulate, rachis not winged, blade smaller than terminal; terminal leaflet (or simple blade) suborbicular or oblong, (0.6-) 1.5-3.5(-4.5) cm × (4-)8-20(-25) mm, base obtuse, cuneate, or subcordate, margins entire or repand, apex obtuse. Fruiting pedicels divaricate or descending, straight or, occasionally, recurved, (7-)9-21(-25) mm. Flowers: sepals 2.5-4 × 1-1.5 mm; petals white or pink, spatulate or obovate, 4.5-6 × 1.5-3 mm, (base to 1 mm), apex rounded; filaments 2.5-3.5 mm; anthers 0.7-1 mm. Fruits 1.4-2.2(-2.7) cm × 1-1.5(-1.8) mm; ovules 30-38(-40) per ovary; style 0.5-1.5(-2) mm. Seeds uniseriate, reddish brown, ovoid, (0.8-)1-1.2 × (0.6-)0.7-0.8(-0.9) mm, moderately reticulate with (75-)100-150(-175) areolae on each side. 2n = 64.

Flowering Jan-Aug. Lake margins, streams, ponds, springs, river shores, seeps, swales, wet meadows; 0-1500 m; introduced; B.C., Man., N.B., Nfld. and Labr. (Nfld.), Ont., P.E.I., Que.; Conn., Idaho, Ind., Ky., Maine, Mass., Mich., N.H., N.Mex., N.Y., Oreg., Pa., R.I., Vt., Wyo.; Europe; introduced also elsewhere in the New World, Australia.

Duration: Perennial

Nativity: Non-Native

Lifeform: Forb/Herb

General: Herbaceous perennials, to 1 m high or taller, stems prostrate, decumbent, or erect in emergent plants, unbrancing, herbage glabrous throughout or sparsely pubescent, plants with pungent, watery sap.

Leaves: Alternate, blades pinnate, 3-11-foliolate, (sometimes simple when submerged) 1.5-15 cm long, terminal leaflet or simple blades suborbicular or oblong, 6-45 mm long and 4-25 mm wide, bases obtuse, cuneate, or subcordate, margins entire or repand, apices obtuse, lateral leaflets sessile or with very short petioles, rachis not winged, petioles not winged but with auriculate bases, basal leaves not in a rosette.

Flowers: White, with 4 petals forming a cross, petals white or pink, spatulate or obovate, 4.5-6 mm long and 1.5-3 mm wide with bases to 1 mm, apices rounded, sepals 4, free, sepals 2.5-4 mm long and 1-1.5 mm wide, stamens 6 with 4 long and 2 short (tetradynamous) filaments 2.5-3.5 mm long, anthers to 1 mm long, ovary solitary and superior, ovules 30-40 per ovary, generally 2-chambered with a septum connecting 2 parietal placentas, styles solitary, 0.5-2 mm long, stigmas entire or 2-lobed, flowers borne in elongated, corymbose and several-flowered racemes (in rounded clusters) at branch tips, infloresences elongated in fruit.

Fruits: Linear to narrowly oblong siliques dihescent into 2 valves and a septum, 14-27 mm long and 1-1.5 mm wide, fruiting pedicels divaricate or descending, straight or occasionally recurved, 7-25 mm long. Seeds 1-many, in a single row (uniseriate) reddish brown

Ecology: Introduced, found in water or wet areas on lake margins, streams, ponds, springs, river shores, seeps, swales, and wet meadows, from 0-5,000 ft (0-1524 m); flowering January-August.

Distribution: Widespread across much of the northern United States, currently only recognized as occurring in New Mexico in the southwest, see USDA Plants or FNA for more information.

Notes: This low-growing cress like to have wet feet, growing in or near water, and has somewhat inconspicuous white flowers, the petals with rounded lobes and the flowers with exserted anthers and styles, with flowers borne in small, rounded, apical clusters, and leaves more similar in appearance (at first glance) to a clover than a mustard due to the rounded lobes of its leaves. The single row of seeds in the fruits are a good identifying trait for this species. This plant has so far only been recognized as occurring in New Mexico in the southwest, and is not treated in older versions of Kearney and Peebles.

Ethnobotany: Unknown.

Synonyms: Rorippa microphylla

Editor: LCrumbacher2012