Sisymbrium sylvestre Linnaeus, Sp. Pl. 2: 657. 1753; Nasturtium sylvestre (Linnaeus) R. Brown; Rorippa liaotungensis X. D. Cui & Y. L. Chang.

Herbs perennial, (5-)15-80(-100) cm tall, glabrous or sparsely pubescent. Stems prostrate, decumbent, ascending, or suberect, branched mainly basally. Rosette leaves soon withered, similar to cauline leaves. Middle cauline leaves petiolate, deeply pinnatisect; petiole not auriculate, rarely minutely auriculate; leaf blade (2-)3.5-15(-20) × (0.7-)1-4.5(-6) cm; lateral lobes 3-6 on each side of midvein, sublinear, lanceolate, oblong, elliptic, or ovate, margin dentate or serrate, sometimes subentire; uppermost leaves with 1-3 lateral lobes or not lobed, often subsessile. Racemes ebracteate. Fruiting pedicels (3-)4-10(-12) mm, slender, divaricate. Sepals green or yellow, oblong, 1.8-3(-3.5) × 0.7-1.5 mm, ascending or spreading. Petals yellow, spatulate or obovate, (2.2-)2.8-5.5(-6) × 1.5-2.5 mm, apex rounded. Filaments (1.5-)1.8-3.5(-4) mm; anthers oblong, 0.7-1 mm. Ovule number highly variable, mostly aborted. Fruit linear, very rarely oblong-linear, (0.4-)0.7-2(-2.5) cm × (0.7-)1-1.3(-1.6) mm, rarely producing seeds; style 0.5-1(-1.5) mm; stigma subentire or slightly 2-lobed. Seeds reddish brown, ovoid, colliculate, uniseriate or rarely subbiseriate, 0.6-0.9 × 0.4-0.5 mm. Fl. and fr. May-Sep. 2n = 32, 40, 48.

Although the present authors have not examined the type of Rorippa liaotungensis, the detailed description and illustration leave no doubt that it is a synonym of R. sylvestris, hundreds of specimens of which were examined from its native and naturalized ranges.

Along ditches, damp areas, meadows, waste grounds, fields; 100-2000 m. Xinjiang, Liaoning [India, Japan, Kashmir, Russia, Tajikistan, Uzbekistan; SW Asia, Europe; introduced in North and South America].