1	Fruits silicles, less than 3 times longer than wide		(2)
+	Fruits siliques, greater than 3 times longer than wide		(13)
2 (1)	Plants aquatic (submerged), rooting from proximal nodes; leaves: submerged pectinate, emergent usually not divided, rarely lobed		(3)
+	Plants terrestrial or of wet habitats, not rooting from nodes; leaves divided or not		(4)
3 (2)	Petals yellow; anthers ovate, 0.7-1 mm; styles (0.5-)1-2.2(-2.5) mm; septums complete.		2 Rorippa amphibia
+	Petals white; anthers linear, 1.7-2.2 mm; styles 2-4 mm; septums reduced to rims.		3 Rorippa aquatica
4 (2)	Fruit valves (3 or) 4(-6); septums fenestrate.		5 Rorippa barbareifolia
+	Fruit valves 2; septums complete		(5)
5 (4)	Fruit valves papillate, strigose, or pilose		(6)
+	Fruit valves glabrous		(8)
6 (5)	Annuals, glabrous; cauline leaves not auriculate; sepals deciduous, 0.7-1.3 mm; petals 0.5-0.8 mm; fruit valves papillate.		21 Rorippa tenerrima (in part)
+	Perennials, hirsute or pilose; cauline leaves sometimes auriculate; sepals persistent, 2-3.5 mm; petals 2.2-4.2 mm; fruit valves strigose or pilose		(7)
7 (6)	Fruit valves strigose; styles glabrous; fruiting pedicels 2-5(-6) mm, glabrous or sparsely hirsute.		6 Rorippa calycina
+	Fruit valves pilose; styles pilose; fruiting pedicels (3-)4-10(-12) mm, densely pilose.		7 Rorippa columbiae
8 (5)	Racemes not or slightly elongated (subumbellate) in fruit; sepals persistent; anthers narrowly oblong, 0.8-1.2 mm.		19 Rorippa subumbellata
+	Racemes elongated in fruit; sepals deciduous; anthers ovate, 0.2-0.6 mm		(9)
9 (8)	Fruits globose or subglobose, 1.2-3.2 mm		(10)
+	Fruits lanceolate, oblong, ovoid, ellipsoid, or pyriform, 2-10(-14) mm		(11)
10 (9)	Perennials, with thickened rhizomes; fruiting pedicels 4-15 mm; petals 3-5 mm; styles 1-1.5(-2) mm.		4 Rorippa austriaca
+	Annuals or biennials, without thickened rhizomes; fruiting pedicels 1.5-3.7(-4.3) mm; petals 0.6-1.2 mm; styles 0.1-0.7(-1) mm.		18 Rorippa sphaerocarpa
11 (9)	Perennials (caudex well-developed); cauline leaf blades: bases not auriculate, not amplexicaul.		1 Rorippa alpina (in part)
+	Annuals or, rarely, short-lived perennials (without caudex); cauline leaf blades: bases sometimes auriculate or amplexicaul		(12)
12 (11)	Stems ascending, decumbent, or prostrate, few to several from base; sepals 0.8-1.8 mm; petals 0.5-1.8 mm.		9 Rorippa curvipes (in part)
+	Stems erect, often simple from base; sepals 1.5-2.4(-2.6) mm; petals (1.5-)1.8-2.5(-3) mm.		14 Rorippa palustris (in part)
13 (1)	Sepals 4-5 mm; petals 6-8 mm.		8 Rorippa crystallina
+	Sepals 0.7-3(-4.5) mm; petals (0-)0.5-5.5(-6) mm		(14)
14 (13)	Petals absent		(15)
+	Petals present (sometimes less than 1 mm)		(16)
15 (14)	Fruits linear, (15-)25-40 × 0.7-0.9(-1) mm; ovules 70-90 per ovary; fruiting pedicels (2-)3-8(-10) mm.		11 Rorippa dubia (in part)
+	Fruits oblong to oblong-linear, (4-)6-9(-12) × (1.4-)1.8-2.8(-3.5) mm; ovules 158-242 per ovary; fruiting pedicels 0.5-2(-4) mm.		16 Rorippa sessiliflora
16 (14)	Fruits oblong to lanceolate, (1.5-)9-10 mm		(17)
+	Fruits linear or, oblong-linear, (8-)10-40 mm		(23)
17 (16)	Cauline leaf blades: bases not auriculate		(18)
+	Cauline (distal) leaf blades: bases auriculate		(19)
18 (17)	Perennials (with caudex); fruit valves glabrous; petals (1.3-)1.5-2 mm.		1 Rorippa alpina (in part)
+	Annuals; fruit valves papillate; petals 0.5-0.8 mm.		21 Rorippa tenerrima (in part)
19 (17)	Plants perennials, glabrous or pubescent, trichomes hemispherical, vesicular; petals 2.5-5.3(-6) mm; styles (0.8-)1-2.5(-3.5) mm		(20)
+	Plants annuals or, rarely, perennials, glabrous or hirsute, trichomes cylindrical; petals 0.5-2.5(-3) mm; styles 0.1-1(-1.2) mm		(21)
20 (19)	Fruiting pedicels straight or, rarely, curved-ascending, 3-5(-6.5) mm; petals 2.5-3.5 × 0.8-1.3 mm.		15 Rorippa ramosa
+	Fruiting pedicels sigmoid or recurved, 4-12(-14.5) mm; petals (2.7-)3.2-5.3(-6) × 1.5-2.5 mm.		17 Rorippa sinuata (in part)
21 (19)	Stems erect, (often simple from base); petals (1.5-)1.8-2.5(-3) mm.		14 Rorippa palustris (in part)
+	Stems ascending or decumbent to prostrate, (usually few- or several-branched from base); petals 0.5-1.8(-2) mm		(22)
22 (21)	Petals erect; fruits ovoid to pyriform.		9 Rorippa curvipes (in part)
+	Petals spreading; fruits oblong to linear.		10 Rorippa curvisiliqua (in part)
23 (16)	Plants pubescent (trichomes vesicular, hemispherical or clavate)		(24)
+	Plants usually glabrous, rarely pubescent (trichomes not vesicular)		(25)
24 (23)	Perennials (rhizomatous); fruiting pedicels sigmoid or recurved, 4-12(-14.5) mm; petals (2.7-)3.2-5.3(-6) mm; ovules (30-)50-82(-98) per ovary.		17 Rorippa sinuata (in part)
+	Annuals or biennials (not rhizomatous); fruiting pedicels straight or curved-ascending, (1.5-)2.3-4.7(-5.3) mm; petals 1-2 mm; ovules (100-)150-210 per ovary.		22 Rorippa teres
25 (23)	Perennials; cauline (distal) leaf blades pinnatisect; petals 1.5-2.5 mm wide; seeds rarely produced.		20 Rorippa sylvestris
+	Annuals or biennials; cauline leaf blades not pinnatisect; petals 0.2-1.5 mm wide; seeds usually produced		(26)
26 (25)	Seeds uniseriate; fruits straight, 0.7-0.9(-1) mm wide.		11 Rorippa dubia (in part)
+	Seeds biseriate, or often nearly so; fruits often curved, 1-2 mm wide		(27)
27 (26)	Petals 0.6-1.8(-2) mm, oblong to oblanceolate, shorter than sepals; median filaments 1-1.7 mm.		10 Rorippa curvisiliqua (in part)
+	Petals 2.5-4(-4.5) mm, obovate or spatulate, longer than sepals; median filaments 1.5-3 mm		(28)
28 (27)	Cauline (distal) leaves sessile, margins entire or denticulate; ovules (60-)70-110 per ovary; styles (0.5-)1-1.5(-2) mm.		12 Rorippa indica
+	Cauline (distal) leaves petiolate, margins pinnately lobed; ovules 42-68 per ovary; styles 0.5-1(-1.2) mm.		13 Rorippa microtitis