Annual, biennial, or short-lived perennial herb from a slender taproot; stems erect, 15-100 cm tall, simple to much branched from base, glabrous to stiff-hairy.
Basal and lower stem leaves oblong to oblanceolate, (4) 6-20 cm long, 0.5-4 cm wide, short-stalked to unstalked, irregularly saw-toothed, incised, deeply cleft, repand, or variously pinnately divided, with slightly clasping, ear-like lobes at the bases, sharp- or long-pointed at the tips; glabrous or stiff-hairy.
Inflorescence of spreading-ascending stalks, 3-14 mm long, glabrous to sparsely hairy; petals light yellow, 1-3.5 mm long, oblong to broadly spoon-shaped; sepals often yellowish or purplish, 1-2 mm long, glabrous.
Siliques, spreading to ascending, straight to somewhat upcurved, 3-14 mm long, 2-3 mm wide, egg-shaped to cylindric or clavate, 1- to 4-carpelled; beaks 0.2-1 mm long, straight, abruptly attached to apex; seeds brown to reddish-brown, mostly 0.4-0.6 mm long, minutely honeycombed and pimpled, 20-80.
At least six poorly defined varieties have been attributed to the BC flora, but are not treated here.
Synonyms and Alternate Names:
Radicula palustris (L.) Moench
Rorippa islandica var. microcarpa (Regel) Fernald
Rorippa palustris subsp. palustris
Rorippa palustris var. reptabunda (Fernald) R. Stuckey
Rorippa palustris var. williamsii (Britton) Hultén
1. Stems and abaxial leaf blade surfaces usually glabrous, rarely sparsely pubescent proximally........... Rorippa palustris subsp. palustris
1. Stems and abaxial leaf blades surfaces often densely hirsute.................Rorippa palustris subsp. hispida
Source: Flora North America online.