1	Cauline leaves (at least some) sessile, blade bases auriculate, sagittate, or amplexicaul		(2)
+	Cauline leaves usually petiolate, blade bases (when sessile) not auriculate, sagittate, or amplexicaul (absent in L. nanum)		(8)
2 (1)	Plants glabrous or sparsely pubescent proximally; uppermost cauline leaf blades: bases cordate-amplexicaul; basal leaf blades: margins 2- or 3-pinnatifid or pinnatisect; petals yellow.		33 Lepidium perfoliatum
+	Plants usually puberulent or hirsute proximally, rarely glabrate; uppermost cauline leaf blades: bases auriculate or sagittate; basal leaf blades: margins usually entire, subentire, dentate, denticulate, lyrate, or sinuate, rarely 1- or 2-pinnatifid; petals (when present) white		(3)
3 (2)	Stamens 2; petals absent or rudimentary; basal leaf blades: margins 1- or 2-pinnatifid; styles usually obsolete (rarely to 0.1 mm).		28 Lepidium oblongum (in part)
+	Stamens 6; petals present (distinct); basal leaf blades: margins usually entire, subentire, dentate, denticulate, lyrate, or sinuate, rarely pinnatifid; styles distinct (0.2 mm or longer)		(4)
4 (3)	Plants not rhizomatous; fruits dehiscent, apically broadly winged, notch present; racemes much-elongated in fruit		(5)
+	Plants rhizomatous; fruits indehiscent, apically not winged, notch absent; racemes not much-elongated (corymbose panicles) in fruit		(6)
5 (4)	Annuals; fruit valves papillate; styles 0.2-0.5(-0.7) mm, included or only slightly exserted beyond apical notch of fruits.		6 Lepidium campestre
+	Perennials (with caudex); fruit valves often not papillate; styles (0.6-)1-1.5 mm, well-exserted beyond apical notch of fruits.		18 Lepidium heterophyllum
6 (4)	Fruits flattened, cordate to subreniform, valves reticulate-veined.		14 Lepidium draba
+	Fruits inflated, globose, subglobose, obovoid, or obcompressed globose, valves not reticulate-veined		(7)
7 (6)	Fruits usually globose, rarely subglobose, (2-)3-4.4(-5) mm wide, valves puberulent; styles 0.5-1.5 mm.		3 Lepidium appelianum
+	Fruits obovoid to subglobose, or obcompressed globose, (3.5-) 4-6.2(-7) mm wide, valves glabrous; styles (0.8-)1.2-2(-2.3) mm.		7 Lepidium chalepense
8 (1)	Valves rugose or rugose-verrucose		(9)
+	Valves usually smooth (rarely minutely papillate in L. jaredii)		(10)
9 (8)	Fruits reniform to ovate-cordate, 2.3-3.4 mm, apical notches absent, ridged; stamens 6.		8 Lepidium coronopus
+	Fruits didymous, 1.3-1.7 mm, apical notches present, not ridged; stamens 2.		13 Lepidium didymum
10 (8)	Subshrubs or perennials (caudex woody, sometimes with persistent petiolar remains)		(11)
+	Annuals or biennials (without woody caudex, without persistent petiolar remains)		(24)
11 (10)	Styles included in apical notch of fruits; stamens 2; petals absent or rudimentary.		32 Lepidium paysonii
+	Styles usually exserted beyond apical notch of fruits, rarely subequaling notch, or notch absent; stamens 6 (or 2 or 4 in L. integrifolium); petals well-developed		(12)
12 (11)	Basal and proximalmost cauline leaf blade margins pinnately lobed		(13)
+	Basal and proximalmost cauline leaf blade margins usually entire, crenate, or dentate, rarely palmately 3-5-lobed (at apex)		(17)
13 (12)	Plants glabrous throughout; basal leaves absent; fruits 4.2-7(-8) mm wide.		17 Lepidium fremontii
+	Plants puberulent (at least on fruiting pedicels or rachises); basal leaves present; fruits (1.5-)1.8-3.6(-4) mm wide		(14)
14 (13)	Fruits broadly obovate; fruiting pedicels puberulent throughout.		19 Lepidium huberi
+	Fruits ovate to suborbicular or oblong; fruiting pedicels puberulent adaxially, rarely glabrous		(15)
15 (14)	Fruits usually ovate to suborbicular, rarely oblong; basal leaf blades: margins 1- or 2-pinnatifid to -pinnatisect; cauline leaf blades: margins often pinnately lobed.		25 Lepidium montanum (in part)
+	Fruits broadly ovate; basal leaf blades: margins pinnately lobed; cauline leaf blades: margins usually entire, rarely dentate		(16)
16 (15)	Perennials or subshrubs; stems (0.7-)1-4.8(-6.1) dm; middle cauline leaf blades (0.7-)1-2(-3) mm wide.		2 Lepidium alyssoides
+	Perennials; stems (3.5-)4.5-16(-18) dm; middle cauline leaf blades (2.5-)4-10 mm wide.		15 Lepidium eastwoodiae (in part)
17 (12)	Plants pulvinate or cespitose; basal leaf blades: margins usually subapically or apically 3-5-toothed or -lobed, rarely entire (L. barnebyanum); fruiting pedicels puberulent throughout		(18)
+	Plants not pulvinate, not cespitose; basal leaf blades: margins entire or uniformly dentate; fruiting pedicels usually puberulent adaxially, rarely glabrous		(21)
18 (17)	Basal leaves rosulate; cauline leaves absent; anthers 1.4-2 mm.		26 Lepidium nanum
+	Basal leaves not rosulate; cauline leaves present; anthers 0.3-0.8 mm		(19)
19 (18)	Basal leaf blades: margins entire; petals 3.2-4.6 mm; fruits 4-5.5(-6.2) mm.		5 Lepidium barnebyanum
+	Basal leaf blades: margins subapically 3-5-lobed or toothed, rarely entire (L. davisii); petals 2-3.5 (-4) mm; fruits 2.5-4(-5) mm		(20)
20 (19)	Plants cespitose; fruits suborbicular to broadly ovate; styles 0.5-1 mm; seeds (1.8-)2-2.3 mm.		10 Lepidium davisii
+	Plants pulvinate; fruits ovate; styles 0.3-0.6 mm; seeds 1.2-1.5 mm.		29 Lepidium ostleri
21 (17)	Fruits obovate to somewhat rhomboid, 7-11 mm; fruiting pedicels glabrous; seeds 3.7-4.5 mm.		41 Lepidium tiehmii
+	Fruits oblong-elliptic, ovate, oblong, or suborbicular, 1.6-4(-4.4) mm; fruiting pedicels usually pubescent or puberulent, sometimes glabrous (less than 6 mm); seeds 0.8-2 mm		(22)
22 (21)	Plants rhizomatous; fruits (1.6-)1.8-2.4(-2.7) mm, apically not winged, notch usually absent; styles 0.05-0.15 mm.		23 Lepidium latifolium
+	Plants not rhizomatous; fruits (2.5-)3-4(-4.4) mm, apically winged, notch present; styles 0.2-1 mm		(23)
23 (22)	Perennials or subshrubs (woody base aboveground); stamens 6; racemes slightly elongated (subcorymbose panicles) in fruit.		9 Lepidium crenatum
+	Perennials (woody base not aboveground); stamens usually 4, rarely 2 or 6; racemes elongated (not corymbose) in fruit.		20 Lepidium integrifolium
24 (10)	Stamens 2		(25)
+	Stamens 4 or 6		(33)
25 (24)	Fruit valves distinctly reticulate-veined; sepals persistent.		39 Lepidium strictum
+	Fruit valves usually not veined (rarely weakly veined); sepals deciduous or, rarely, tardily so		(26)
26 (25)	Fruits 1.7-2.1 × 1.2-1.6 mm; plants puberulent with clavate trichomes.		38 Lepidium sordidum
+	Fruits 1.8-7 × 1.5-5(-5.6) mm; plants puberulent, hirsute, or hispid with cylindrical trichomes		(27)
27 (26)	Fruiting pedicels often strongly flattened, 0.2-0.7 mm wide; fruit valves hirsute to hispid (sometimes only on margins).		22 Lepidium lasiocarpum
+	Fruiting pedicels terete or only slightly flattened, 0.1-0.3(-4) mm wide; fruit valves glabrous or puberulent (at least on margins)		(28)
28 (27)	Fruits elliptic		(29)
+	Fruits obovate, suborbicular, or orbicular		(30)
29 (28)	Basal leaf blades pinnatifid; racemes slightly elongated in fruit, rachises with curved trichomes; fruiting pedicels usually puberulent adaxially, rarely throughout.		35 Lepidium ramosissimum
+	Basal leaf blades (1- or) 2- or 3-pinnatisect; racemes considerably elongated in fruit, rachises with straight trichomes; fruiting pedicels puberulent throughout.		36 Lepidium ruderale
30 (28)	Plants hirsute; basal leaf blade margins pinnatifid		(31)
+	Plants puberulent or glabrous; basal leaf blade margins dentate, serrate, lyrate, or pinnatifid		(32)
31 (30)	Stems often simple from base; rachises pubescent, trichomes curved with fewer, longer, straight ones.		4 Lepidium austrinum
+	Stems often several from base; rachises hirsute, trichomes mostly straight.		28 Lepidium oblongum (in part)
32 (30)	Fruits obovate to obovate-suborbicular, widest beyond middle; rachises with straight, slender to subclavate trichomes; petals absent or rudimentary, 0.3-0.9 mm; cotyledons incumbent.		11 Lepidium densiflorum
+	Fruits orbicular, widest at middle; rachises usually with curved, cylindrical trichomes, rarely glabrous; petals usually present, rarely rudimentary, 1-2(-2.5) mm; cotyledons usually accumbent, rarely incumbent.		42 Lepidium virginicum
33 (24)	Stamens 4; styles usually obsolete, rarely to 0.1 mm, usually included in, or equaling, apical notch of fruits		(34)
+	Stamens 6; styles (0.1-)0.2-1.6 mm, usually exserted beyond, rarely subequaling or included in, apical notch of fruits		(39)
34 (33)	Fruiting pedicels terete or slightly flattened, 0.1-0.3 mm wide		(35)
+	Fruiting pedicels strongly flattened, 0.4-1.4 mm wide		(36)
35 (34)	Fruits 2.4-3.6 mm, apically winged, apical notches 0.3-0.8 mm deep; stamens all median; petals absent.		30 Lepidium oxycarpum
+	Fruits 1.8-2 mm, apically not winged, apical notches 0.05-0.1 mm deep; stamens 2 median, 2 lateral; petals present (rudimentary, 0.4-0.6 mm).		34 Lepidium pinnatifidum
36 (34)	Sepals somewhat persistent; fruit valves hirsute (trichomes spreading, mixed with smaller ones); petals usually pubescent on outside, rarely glabrescent, with fringed margin; racemes compact, subcapitate to cylindrical in fruit.		24 Lepidium latipes
+	Sepals deciduous; fruit valves glabrous or (sparsely, uniformly) puberulent, pubescent, or hirsute (sometimes only on margin); petals usually absent, when present, glabrous, without fringed margin; racemes lax or somewhat dense, not compact in fruit		(37)
37 (36)	Petals usually present, rarely rudimentary or absent; fruit valves slightly veined or not; fruiting pedicels not appressed to rachises.		27 Lepidium nitidum
+	Petals absent; fruit valves strongly reticulate-veined; fruiting pedicels appressed to rachises or distally recurved		(38)
38 (37)	Fruits (3-)4-6 × 2.5-3.5 mm, apical notches (0.8-)1-2 mm deep, V-shaped; fruiting pedicels (2-)3-4.2 mm.		1 Lepidium acutidens
+	Fruits 2.5-3.5 × 2-2.8 mm, apical notches 0.5-0.7(-0.8) mm deep (closed), often U-shaped; fruiting pedicels (1.6-)1.9-2.5(-3) mm.		12 Lepidium dictyotum
39 (33)	Fruiting pedicels suberect to ascending, subappressed to rachises; fruits (4-) 5-6.4(-7) mm; styles usually included in, rarely subequaling, apical notch of fruits; cotyledons 3-lobed.		37 Lepidium sativum
+	Fruiting pedicels divaricate-ascending to horizontal or descending, not appressed to rachises; fruits 2-3.8(-4.2) mm; styles exserted from apical notch of fruits; cotyledons entire		(40)
40 (39)	Petals usually yellow (rarely creamy white at early anthesis, or fading whitish)		(41)
+	Petals white		(42)
41 (40)	Fruiting pedicels (2.7-)3-4.4(-5) mm, glabrous adaxially; racemes dense, slightly elongated (corymbose to subcapitate) in fruit, rachises glabrous adaxially; fruits divergently winged apically, apical notches 0.2-0.6 mm deep.		16 Lepidium flavum
+	Fruiting pedicels 5-15 mm, pilose adaxially; racemes lax, much-elongated in fruit, rachises usually pilose, rarely glabrous; fruits not winged apically, apical notches 0(-0.1) mm deep.		21 Lepidium jaredii
42 (40)	Filaments puberulent.		31 Lepidium papilliferum
+	Filaments glabrous		(43)
43 (42)	Annuals; rachises pilose, trichomes straight.		40 Lepidium thurberi
+	Annuals or biennials; rachises puberulent, trichomes straight or curved		(44)
44 (43)	Petals suborbicular, 1.5-2.5 mm wide; cauline leaf blades lanceolate or oblanceolate to linear; stems (3.5-)4.5-16(-18) dm, often simple from base.		15 Lepidium eastwoodiae (in part)
+	Petals spatulate to oblanceolate, 1.3-1.8 mm wide; cauline leaf blades often pinnatifid to pinnatisect, sometimes linear; stems 0.4-5(-7) dm, simple or few to several from base.		25 Lepidium montanum (in part)