Rorippa palustris
bog yellow cress, common yellow-cress, hispid yellowcress, marsh cress, marsh yellow-cress
(often simple from base), erect, branched distally, (0.5–)1–10(–14) dm, (sometimes hirsute proximally).
rosulate;
blade [(4–)6–20(–30) cm × 10–50(–80) mm] margins lyrate-pinnatisect, (abaxial surface sometimes hirsute).
petiolate or subsessile;
blade lyrate-pinnatisect, (lateral lobes oblong or ovate when present), (1.5–)2.5–10(–18) cm × (5–)8–25(–30) mm, (lateral lobes smaller than terminal), base auriculate or amplexicaul, margins subentire or irregularly dentate, sinuate, serrate, or crenate, (abaxial surface sometimes hirsute).
often considerably elongated.
sepals erect, oblong, 1.5–2.4(–2.6) × 0.5–1 mm;
petals yellow or pale yellow, spatulate, (1.5–)1.8–2.5(–3) × 0.5–1.5(–2) mm;
median filaments 1–2.5 mm;
anthers ovate, 0.3–0.5 mm.
divaricate or slightly to strongly reflexed, straight or curved, (2.5–)3–10(–14) mm.
usually silicles, rarely siliques, often slightly curved, oblong, ellipsoid, or oblong-ovoid, (2.5–)4–10 × (1.5–)1.7–3(–3.5) mm;
ovules 20–90 per ovary;
style 0.2–1(–1.2) mm.
biseriate, brown to yellowish brown, ovoid or subglobose, 0.5–0.7(–0.9) mm (0.4–0.6(–0.7) mm diam.), colliculate.
Rorippa palustris
Subspecies 2 (2 in the flora).
Rorippa palustris is a highly variable species with controversial infraspecific taxonomy. B. Jonsell (1968) recognized four subspecies, of which one (subsp. palustris) is cosmopolitan and three are North American. R. L. Stuckey (1972) followed Jonsell but further divided the North American plants into eleven, poorly defined varieties. Division of the species into subspecies based solely on stem height and fruit length is artificial. The variation is continuous in every character, and the recognized infraspecific taxa represent only some of the extremes. Some collections cannot be adequately assigned to a given subspecies or variety, and of all the infraspecific taxa recognized, only two can be consistently separated from each other; they are recognized here as subspecies.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
1. Stems and abaxial leaf blade surfaces usually glabrous, rarely sparsely pubescent proximally. | subsp. palustris |
1. Stems and abaxial leaf blades surfaces often densely hirsute. | subsp. hispida |
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MI Flora, 
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PNW Herbaria, Turner Photog. 
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