Perennial herb 20 cm - 0.6 m tall Stem: upright, usually branched above, mostly hairless. Leaves: alternate, deeply pinnately divided, thin-stalked, oblong, tips of segments pointed, sharply toothed, mostly hairless. Lower leaves to 20 cm long and more than 2 cm wide. Upper leaves progressively reduced. Flowers: in loose, branched clusters (racemes). Flower stalks curved, 5 - 10 mm long, and widely divergent or bent downward when mature. Sepals four, ascending. Petals four, yellow, 4 - 5 mm long, twice as long as sepals. Fruit: a long, narrow pod (silique), sometimes drooping, 10 - 15 mm long, 1.5 mm wide, nearly straight, more or less round in cross-section, with a 0.5 - 1 mm long beak. The siliques rarely swell and produce seed, propagation being mostly by means of perennial creeping roots.
Similar species: No information at this time.
Flowering: mid-May to early August
Habitat and ecology: Introduced from Eurasia. Frequent along the muddy margins of streams, usually in places where competition is light. Also found in wet waste ground and other moist to wet areas.
Occurence in the Chicago region: non-native
Etymology: Rorippa possibly comes from the Latin roro, meaning "to be moist," and ripa, meaning riverbank. Sylvestris means "of the woods" and "growing wild."
Author: The Morton Arboretum
From Flora of Indiana (1940) by Charles C. Deam
Local or infrequent on the alluvial bottoms of streams throughout the state except along the muddy slopes of the bank of the Ohio River where it is frequent to common. This is a pernicious weed and should be destroyed as soon as it is discovered. It is best exterminated by the application of some reliable weed killer.
Indiana Coefficient of Conservatism: C = null, non-native
Erect perennial 2-6 dm, usually branched above, glabrous or sparingly hirsute on the lower part of the stem; basal rosettes present in young plants; cauline lvs slender-petiolate, oblong, deeply pinnatifid or divided into numerous oblong or obovate segments, the lower lvs to 2 dm, more than 2 cm wide, the upper progressively reduced, the segments mostly acute, sharply or angularly toothed or in depauperate pls subentire; pet 4-5 mm, twice as long as the sep; mature pedicels widely divergent or somewhat deflexed, often arcuate, 5-10 mm; frs nearly straight, 10-15 נ1.5 mm, the style 0.5-1 mm; seeds often wanting; 2n=32, 40, 48. Native of Eurasia, intr. in wet soil nearly throughout our range. May-Aug. (Radicula s.)
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.