1. Plant truly aquatic, the submersed leaves dissected in a bipinnate pattern into filiform segments (midvein present, the lateral segments again dissected), frequently detaching readily from the stem; petals white.
1. Plant terrestrial or aquatic but even if in water the leaves with definite flat lobes (not bipinnately dissected) and not falling from the stem; petals yellow.
2. Uppermost leaves (including those at base of branches of the inflorescence) deeply pinnatifid (lobed nearly or quite to the midrib); fruit linear, the ovary soon becoming more than 5 times as long as wide, but not (in Michigan) forming ripe seed; petals 2.5–3.7 mm long, distinctly exceeding the sepals.
2. Uppermost leaves often merely toothed or shallowly lobed; fruit nearly spherical to short-oblong or cylindrical, no more than 5 times as long as wide, normally setting copious seed; petals 0.5–2.3 mm long, barely if at all longer than the sepals (often shorter).
3. Pedicels of mature fruit somewhat curved or arching downwards; petals ca. 1 mm long or shorter; leaves all glabrous beneath; mature fruit ca. 2–5.2 mm long, up to 1.7 mm thick, mostly broadest well below the middle, strongly tapering to ± acute apex.
3. Pedicels of mature fruit usually ± straight, ascending or spreading; petals ca. (1–) 1.5–2.3 mm long; leaves glabrous or hispid beneath; mature fruit thicker, the largest on a plant (1.6–) 2–2.7 mm thick at or near the middle, not strongly tapering, the apex blunter.
All species found in Rorippa
MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. December 13, 2017. http://michiganflora.net/genus.aspx?id=Rorippa.