Brassicaceae
Herbs or subshrubs [shrubs or, rarely, lianas or trees], annual, biennial, or perennial; usually terrestrial, rarely submerged aquatics; with pungent watery juice; scapose or not; pubescent or glabrous, usually without papillae or tubercles (multicellular glandular papillae or tubercles present in Bunias, Chorispora, and Parrya); taprooted or rhizomatous (rarely stoloniferous), caudex simple or branched, sometimes woody, rhizomes slender or thick. Trichomes unicellular, simple, stalked, or sessile; forked, stellate, dendritic, malpighiaceous (medifixed, 2-fid, appressed), or peltate and scalelike, eglandular. Stems (absent in Idahoa, sometimes Leavenworthia) usually erect, sometimes ascending, descending, prostrate, decumbent, or procumbent; branched or unbranched. Leaves (sometimes persistent) cauline usually present, basal present or not (sometimes rhizomal present in Cardamine), rosulate or not, usually alternate (sometimes opposite or whorled in Cardamine angustata, C. concatenata, and C. diphylla and in Lunaria annua; sometimes subopposite in C. dissecta and C. maxima and in Draba ogilviensis), usually simple, rarely trifoliolate or pinnately, palmately, or bipinnately compound; stipules absent [with tiny, stipulelike glands at base of petioles and pedicels]; petiolate, sessile, or subsessile (sessile auriculate or not, sometimes amplexicaul); blade margins entire, dentate, crenate, sinuate, repand, or dissected. Inflorescences terminal, usually racemose (racemes often corymbose or paniculate) or flowers solitary on pedicels from axils of rosette leaves; bracts usually absent, sometimes present. Pedicels present (persistent or caducous [rarely geotropic]). Flowers bisexual [unisexual], usually actinomorphic (zygomorphic in Iberis, sometimes in Pennellia, Streptanthus, and Teesdalia); perianth and androecium hypogynous; sepals usually caducous, rarely persistent, 4, in 2 decussate pairs (1 pair lateral, 1 median), distinct [connate], not saccate or lateral (inner) pair (or, rarely, both pairs) saccate, forming tubular, campanulate, or urceolate calyx; petals 4, alternate with sepals, usually cruciform, rarely in abaxial and adaxial pairs, rarely rudimentary or absent, claw differentiated or not from blade, blade sometimes reduced and much smaller than well-developed claw, basally unappendaged, or, rarely, appendaged, margins entire or emarginate to 2-fid, rarely pinnatifid [fimbriate or filiform]; stamens (2 or 4) 6 [8–24], in 2 whorls, usually tetradynamous (lateral outer pair shorter than median inner 2 pairs), rarely equal in length or in 3 pairs of unequal length; filaments (slender, sometimes winged, appendaged, or toothed): median pairs usually distinct, rarely connate; anthers dithecal, dehiscing by longitudinal slits, pollen grains 3(–11)-colpate, trinucleate; nectar glands receptacular, variable in number, shape, size, and disposition around filament base, always present opposite bases of lateral filaments, median glands present or absent; disc absent; pistil 1, 2-carpellate; ovary 2-locular with false septum connecting 2 placentae, rarely 1-locular and eseptate, placentation usually parietal, rarely apical; gynophore usually absent; style 1, persistent [caducous], sometimes obsolete or absent; stigma capitate or conical, entire or 2-lobed, lobes spreading or connivent, sometimes decurrent, distinct or connate, rarely elongated into horns or spines; ovules 1–300 per ovary, anatropous or campylotropous, bitegmic, usually crassinucellate, rarely tenuinucellate. Fruits usually capsular, usually 2-valved ((3 or) 4(–6) in Rorippa barbareifolia, (2 or) 4 in Tropidocarpum capparideum), termed siliques if length 3+ times width, or silicles if length less than 3 times width, sometimes nutletlike, lomentaceous, samaroid, or schizocarpic and [with] without a carpophore carrying the 1-seeded mericarp, dehiscent or indehiscent, segmented or not, torulose or smooth, terete, angled, or flat, often latiseptate (flattened parallel to septum) or angustiseptate (flattened at right angle to septum); gynophore usually absent, sometimes distinct; valves each not or obscurely veined, or prominently 1–7-veined, usually dehiscing acropetally, rarely basipetally, sometimes spirally or circinately coiled, glabrous or pubescent [spiny or glochidiate]; replum (persistent placenta) rounded, flattened, or indistinct (obsolete in Crambe, often perforate in Thysanocarpus); septum complete, perforated, reduced to a rim, or absent (obsolete in Crambe and Thysanocarpus, not differentiated from replum in Raphanus), sometimes with a midvein or anastomosing veins. Seeds usually yellow or brown, rarely black or white, flattened or plump, winged or not, or narrowly margined, ovoid, oblong, globose, or ovate, usually uniseriate or biseriate, sometimes aseriate, per locule, mucilaginous or not when wetted; embryo usually strongly curved, rarely straight with tiny radicle; cotyledons entire, emarginate, 3[2]-fid to base, orientation to radicle: incumbent (embryo notorrhizal: radicle lying along back of 1 cotyledon), accumbent (embryo pleurorrhizal: radicle applied to margins of both cotyledons), conduplicate (embryo orthoplocal: cotyledons folded longitudinally around radicle), or spirally coiled (embryo spirolobal) [twice transversely folded (embryo diplecolobal)]; endosperm absent (germination epigeal).
Contents
- 1 Distribution
- 2 Discussion
- 3 Selected References
- 4 Lower Taxa
- 5 Illustrations
- 6 Keys
- 6.1 Key to Genera Based Primarily on Flowering Specimens
- 6.2 Key to Genera of Group 1
- 6.3 Key to Genera of Group 2
- 6.4 Key to Genera of Group 3
- 6.5 Key to Genera of Group 4
- 6.6 Key to Genera Based Primarily on Fruiting Specimens
- 6.7 Key to Genera of Group 5
- 6.8 Key to Genera of Group 6
- 6.9 Key to Genera of Group 7
- 6.10 Key to Genera of Group 8
Distribution
Nearly worldwide, especially temperate areas, with the highest diversity in the Irano-Turanian region, Mediterranean area, and western North America.
Discussion
Genera ca. 338, species ca. 3780 (97 genera, 744 species in the flora).
Of the 634 species of Brassicaceae (mustards or crucifers) native in the flora area, 616 (418 endemic) grow in the United States, 140 (12 endemic) in Canada, and 31 (1 endemic) in Greenland.
The latest comprehensive account of the Brassicaceae for North America (R. C. Rollins 1993) included Mexico and Central America and excluded Greenland. In that account, 667 native species were recognized for the continent; I place 37 of those in the synonymy of other species. Of the remaining 630 species, 111 are restricted to Mexico and Central America, and 519 are native to the flora area. This last number falls 114 species short of the 634 native species that I recognize in the flora area. Since Rollins’s account, 50 species were added to the flora in the past 15 years. Of these, 35 species were described as new, ten were added as native but previously overlooked or misidentified, and five have since become naturalized. Additionally, 72 species recognized in this treatment were treated by Rollins as either synonyms or infraspecific taxa of other species. The generic placement of 158 species in this account differs drastically from that in Rollins, though most of the changes involve the transfer of most of his species of Arabis to Boechera (59 spp.) and of Lesquerella to Physaria (54 spp.). The generic circumscriptions adopted herein are fully compatible with the rapidly accumulating wealth of molecular data, and all genera recognized here are monophyletic. Some examples demonstrate the differences between the two treatments. Arabis, in the sense of Rollins, included 80 species and 64 varieties; in this account, those 144 taxa are assigned to six genera in five tribes: Arabidopsis (2 spp.; tribe Camelineae), Arabis (16 spp.; tribe Arabideae), Boechera (109 spp.; tribe Boechereae), Pennellia (2 spp.; tribe Halimolobeae), Streptanthus (1 sp.; tribe Thelypodieae), and Turritis (1 sp.; tribe Camelineae). A similar division involves Thlaspi, a genus recognized by Rollins to include nine species, of which two are retained here in Thlaspi (tribe Thlaspideae), one is placed in Microthlaspi, and three in Noccaea (both in tribe Noccaeeae), two are reduced to synonymy of the latter genus, and one species of Noccaea is endemic to Mexico. Lepidium in this treatment includes Rollins’s Cardaria, Coronopus, and Stroganowia; Hesperidanthus includes his Caulostramina, Glaucocarpum, and Schoenocrambe (excluding its type).
The Brassicaceae include important crop plants that are grown as vegetables (e.g., Brassica, Eruca, Lepidium, Nasturtium, Raphanus) and condiments (Armoracia, Brassica, Eutrema, Sinapis). Vegetable oils of some species of Brassica, including B. napus (canola), probably rank first in terms of the world’s tonnage production. The Eurasian weed Arabidopsis thaliana (thale or mouse-ear cress) has become the model organism in experimental and molecular biology. The family also includes ornamentals in the genera Aethionema, Alyssum, Arabis, Aubrieta, Aurinia, Erysimum, Hesperis, Iberis, Lobularia, Lunaria, Malcolmia, and Matthiola. Finally, the flora includes 106 species of weeds from southwest Asia and Europe (R. C. Rollins and I. A. Al-Shehbaz 1986), of which 11 species of Lepidium have become noxious weeds in western North America.
The Brassicaceae have been regarded as a natural group for over 250 years, beginning with their treatment by Linnaeus in 1753 as the “Klass” Tetradynamia. More recently and based on a limited sampling of genera, W. S. Judd et al. (1994) recommended that the Brassicaceae and Capparaceae (including Cleomaceae) be united into one family, Brassicaceae. Molecular studies (J. C. Hall et al. 2002) suggested that three closely related families be recognized, with Brassicaceae sister to Cleomaceae, and both sister to Capparaceae. All three families have consistently been placed in one order (e.g., Capparales or Brassicales) by A. Cronquist (1988), A. L. Takhtajan (1997), and J. E. Rodman et al. (1996, 1998), as well as by the Angiosperm Phylogeny Group (APG) (http://www.mobot.org/MOBOT/research/APweb/). Brassicales includes families uniquely containing glucosinolates (mustard-oil glucosides), myrosin cells, racemose inflorescences, superior ovaries, often-clawed petals, and a suite of other characteristics (see the APG website).
Tribal classification of Brassicaceae has been subject to controversy. O. E. Schulz’s (1936) classification has been used for over 70 years, though many botanists (e.g., E. Janchen 1942; I. A. Al-Shehbaz 1984; M. Koch et al. 1999; O. Appel and Al-Shehbaz 2003; Koch et al. 2003; M. A. Beilstein et al. 2006; Al-Shehbaz et al. 2006) amply demonstrated the artificiality of that system. Schulz divided the family into 19 tribes and 30 subtribes based on characters (e.g., fruit length-to-width ratio, compression, dehiscence; cotyledonary position; sepal orientation) that exhibit tremendous convergence throughout the family. Of these, only the tribe Brassiceae was previously shown to be monophyletic.
Several molecular studies (e.g., R. A. Price et al. 1994; J. C. Hall et al. 2002; M. Koch 2003; T. Mitchell-Olds et al. 2005; C. D. Bailey et al. 2006; M. A. Beilstein et al. 2006, 2008) have demonstrated that the Brassicaceae are split into two major clades: the Mediterranean-Southwest Asian Aethionema and its sister clade that includes the rest of the family. Although Beilstein et al. showed that the family, excluding Aethionema, is divided into three major clades, such subdivision was based on only ca. 30% of the total number of genera. These three major clades still hold when nearly all genera of the family are investigated (S. I. Warwick et al., unpubl.).
Tribal assignments in the flora area are based on critical evaluation of morphology in connection with all published molecular data. To date, about 230 of the 338 genera of the family are placed in 35 tribes, including all large genera, which account for over 70% of the total species. Most of the remaining 108 genera would likely be assigned to the 35 tribes, be placed in new, smaller tribes, or be reduced to synonymy of larger genera. The delimitation of tribes for the flora area follows I. A. Al-Shehbaz et al. (2006), Al-Shehbaz and S. I. Warwick (2007), and D. A. German and Al-Shehbaz (2008) and differs from that of O. E. Schulz (1936) and the subsequent adjustments proposed by E. Janchen (1942) and Al-Shehbaz (1984, 1985, 1985b, 1986, 1987, 1988, 1988b, 1988c). Some of the tribes (e.g., Brassiceae and Lepidieae) are easily distinguished by relatively few characters; others (e.g., Arabideae, Camelineae, and Thelypodieae) are more difficult to separate unless a larger suite of characters is used. Because of the incomplete molecular knowledge on all genera of the family, the tribes, their genera, and species are listed herein alphabetically. Both R. C. Rollins (1993) and O. Appel and Al-Shehbaz (2003) arranged the genera alphabetically throughout, and the only difference in this account is the placement together of closely related genera within well-established monophyletic tribes.
Morphological data alone are sometimes unreliable in establishing phylogenetic relationships within Brassicaceae. Convergence is common throughout the family, and almost all morphological characters, especially of the fruits and embryos, which are quite heavily utilized in the delimitation of the genera and tribes, evolved independently. For example, rare character states, such as the spirolobal cotyledons, are known in at least three genera of three tribes (Bunias, Buniadeae; Erucaria, Brassiceae; Heliophila, Heliophileae), and lianas evolved independently in the South American Cremolobus (Cremolobeae), the South African Heliophila, and the Australian Lepidium (Lepidieae). Similarly, the reduction of chromosome number in the family to n = 4 occurred independently in two species of the Australian Stenopetalum and in at least 11 species of the North American Physaria. Other character states (e.g., zygomorphy, apetaly, reduction of stamen number to four, connation of median filaments, etc.) also evolved independently. Reexamination of morphology in light of molecular data is essential in order to understand the role of homoplasy and the evolution of various character states.
The literature on chromosome numbers of Brassicaceae is rather extensive, and rarely is an individual work cited herein in that regard. Instead, the recently compiled cytological data for the entire family (S. I. Warwick and I. A. Al-Shehbaz 2006) are consulted for all species.
Because the size of ovules is relatively small, it is very difficult to determine the number of ovules per ovary. The number of ovules per ovary is based on the sum of mature seeds and aborted ovules in the fruit. The length of style and type of stigma are also taken from the fruits, and the length of fruiting pedicels is measured from several proximal pedicles of the infructescence. Elevation ranges are normally given for a taxon; unfortunately, the range is not known for some taxa.
Generic delimitation in Brassicaceae is often difficult because most genera are distinguished primarily by fruit characters. The following artificial keys emphasize either flowering or fruiting characters, and the most reliable identification of a given plant to a genus can be achieved when specimens have both flowers and fruits, and when both keys are successfully used to identify it to the same genus. The keys are based on species rather than generic descriptions so that all of the morphological manifestations in a given genus are covered and, therefore, a genus may appear multiple times within one of the first four key groups. For example, genera with highly diversified vegetative and floral morphology (e.g., Cardamine, Caulanthus, Lepidium, and Streptanthus) appear in the keys to groups multiple times. Because of such coverage, keys to flowering material incorporate characteristics of a species, or groups of species, rather than of genera. Leads marked (¤) in keys for groups 1–4 indicate that mature fruits and seeds are needed for the identification of genera in their subordinate couplet(s).
Selected References
Lower Taxa
Illustrations
Keys
Key to Genera Based Primarily on Flowering Specimens
| 1 | Trichomes simple or absent | > 2 |
| 1 | Trichomes (at least some) branched | > 3 |
| 2 | Cauline leaves absent or, when present, petiole or blade bases sometimes auriculate or amplexicaul | Group 1 |
| 2 | Cauline leaves present, petiole or blade bases not auriculate | Group 2 |
| 3 | Ovaries and young fruits linear | Group 3 |
| 3 | Ovaries and young fruits not linear | Group 4 |
Key to Genera of Group 1
| 1 | Plants scapose; cauline leaves absent | > 2 |
| 1 | Plants not scapose; cauline leaves present, some blade bases auriculate to amplexicaul | > 8 |
| 2 | Flowers solitary (pedicellate from basal rosettes) | > 3 |
| 2 | Flowers in racemes or corymbs | > 4 |
| 3 | Petals lavender, orange, yellow, or white, considerably longer than sepals, differentiated into blade and claw; se United States. | Leavenworthia |
| 3 | Petals white, slightly longer than sepals, not differentiated into blade and claw; British Columbia, Pacific and some Mountain states. | Idahoa |
| 4 | Petals yellow. | Diplotaxis |
| 4 | Petals white, lavender, or purple | > 5 |
| 5 | Perennials; petals 4-23 mm | > 6 |
| 5 | Annuals; petals 0.5-2.5 mm or absent | > 7 |
| 6 | Petals often white, 0.8-1.5(-2) mm wide; plants eglandular. | Cardamine |
| 6 | Petals usually purple or lavender, rarely white, 3-8 mm wide; plants often with glandular papillae. | Parrya |
| 7 | Leaf blades linear or subulate, margins entire; plants littoral or aquatic. | Subularia |
| 7 | Leaf blades lanceolate to oblanceolate or obovate, margins sometimes lobed; plants terrestrial. | Teesdalia |
| 8 | Racemes bracteate throughout. | Streptanthus |
| 8 | Racemes ebracteate or proximalmost flowers bracteate | > 9 |
| 9 | Cauline leaves petiolate | > 10 |
| 9 | Cauline leaves sessile | > 14 |
| 10 | Cauline leaves compound | > 11 |
| 10 | Cauline leaves simple | > 12 |
| 11 | Plants terrestrial, not rooting from proximal nodes. | Cardamine |
| 11 | Plants aquatic, rooting from proximal nodes. | Nasturtium |
| 12 | Cauline leaf blade margins usually dentate or serrate, rarely subentire. | Iodanthus |
| 12 | Cauline leaf blade margins runcinate or pinnatifid | > 13 |
| 13 | Bases of lateral sepals saccate; petals (12-)16-25(-32) mm. | Orychophragmus |
| 13 | Bases of lateral sepals not saccate; petals 6-10 mm. | Coelophragmus |
| 14 | Stamens 2. | Lepidium |
| 14 | Stamens 6, rarely 4 | > 15 |
| 15 | Stamens exserted; ovaries and young fruits on distinct gynophores | > 16 |
| 15 | Stamens (at least some) included; ovaries and young fruits sessile or on obsolete gynophores | > 19 |
| 16 | Racemes not or slightly elongated in fruit; filaments often puberulent basally; se United States. | Warea |
| 16 | Racemes elongated in fruit; filaments glabrous; Pacific and Mountain states | > 17 |
| 17 | Stigmas 2-lobed; stamens tetradynamous. | Thelypodiopsis |
| 17 | Stigmas entire; stamens subequal | > 18 |
| 18 | Sepals spreading to reflexed; petals usually yellow, rarely white, 12-25 mm. | Stanleya |
| 18 | Sepals erect to ascending; petals purple or white, 6-12(-16) mm. | Thelypodium |
| 19 | Stamens often in 3 pairs of unequal length; petal margins crisped and/or channeled ( ¤) | > 20 |
| 19 | Stamens tetradynamous; petal margins not or rarely crisped, not channeled | > 21 |
| 20 | Fruits terete; seeds not winged. | Caulanthus |
| 20 | Fruits latiseptate; seeds often winged. | Streptanthus |
| 21 | Petals yellow | > 22 |
| 21 | Petals white, lavender, pink, purple, or violet | > 30 |
| 22 | Ovules 1 or 2 per ovary | > 23 |
| 22 | Ovules (4-)10-94 per ovary | > 25 |
| 23 | Basal and proximal cauline leaf blade margins 2- or 3-pinnatifid or pinnatisect. | Lepidium |
| 23 | Basal and proximal cauline leaf blade margins usually entire, dentate, sinuate, or runcinate, rarely pinnatifid | > 24 |
| 24 | Fruiting pedicels reflexed. | Isatis |
| 24 | Fruiting pedicels erect (appressed). | Myagrum |
| 25 | Calyces urceolate; petal margins crisped. | Thelypodiopsis |
| 25 | Calyces not urceolate; petal margins not crisped | > 26 |
| 26 | Fruiting pedicels reflexed; petal claws not attenuate. | Caulanthus |
| 26 | Fruiting pedicels divaricate to erect; petal claws attenuate | > 27 |
| 27 | Petals (6-)8-30 mm, claws distinct. | Brassica |
| 27 | Petals 0-9(-12) mm, claws absent | > 28 |
| 28 | Cauline leaf blade bases cordate-amplexicaul. | Conringia |
| 28 | Cauline leaf blade bases auriculate | > 29 |
| 29 | Ovaries and young fruits linear; stems angular distally. | Barbarea |
| 29 | Ovaries and young fruits usually globose, ovoid, or oblong (if linear, petals absent or 0.5-4 mm); stems seldom angular distally. | Rorippa |
| 30 | Ovaries and young fruits ovate, orbicular, or cordate | > 31 |
| 30 | Ovaries and young fruits linear | > 36 |
| 31 | Ovules usually 1 or 2 per ovary, if 4 (some Lepidium), style distinct | > 32 |
| 31 | Ovules (4-)6-16 per ovary | > 34 |
| 32 | Plants usually pubescent; ovules 2(-4) per ovary. | Lepidium |
| 32 | Plants glabrous, rarely sparsely pubescent; ovules 1 per ovary | > 33 |
| 33 | Cauline leaf blade margins dentate or subentire; fruits terete, ovoid or ellipsoid; plants glabrous. | Calepina |
| 33 | Cauline leaf blade margins usually subentire, dentate, pinnatifid, or pinnatisect, rarely entire; ovaries latiseptate, orbicular to ovate, or elliptic; plants glabrous or pubescent. | Thysanocarpus |
| 34 | Perennials or, rarely, biennials. | Noccaea |
| 34 | Annuals ( ¤) | > 35 |
| 35 | Seed coats smooth; cauline leaf blade margins entire; plants not fetid. | Microthlaspi |
| 35 | Seed coats striate or coarsely reticulate; cauline leaf blade margins often dentate; plants often fetid. | Thlaspi |
| 36 | Petals not differentiated into blade and claw, gradually narrowed basally | > 37 |
| 36 | Petals differentiated into blade and claw | > 39 |
| 37 | Biennials or perennials; young fruits latiseptate. | Boechera |
| 37 | Annuals; young fruits terete | > 38 |
| 38 | Cauline leaf blade bases sagittate-amplexicaul; stigmas entire. | Eutrema |
| 38 | Cauline leaf blade bases auriculate; stigmas 2-lobed, rarely entire. | Thelypodiopsis |
| 39 | Petal claws not attenuate; fruits reflexed. | Caulanthus |
| 39 | Petal claws attenuate; fruits erect to divaricate | > 40 |
| 40 | Petals magenta or purple with deeper purple center. | Streptanthus |
| 40 | Petals white, lavender, or purple, without deeper purple center | > 41 |
| 41 | Petals 15-30 × 6-12 mm, claws 7-15 mm. | Brassica |
| 41 | Petals 2.5-15(-22) × 1-5(-9) mm, claws 1-6(-11) mm | > 42 |
| 42 | Perennials; e, c United States. | Iodanthus |
| 42 | Annuals, biennials, or perennials; sw, w United States | > 43 |
| 43 | Stigmas 2-lobed. | Thelypodiopsis |
| 43 | Stigmas entire | > 44 |
| 44 | Annuals (biennials); petioles not ciliate; w Texas. | Dryopetalon |
| 44 | Biennials or, rarely, perennials; petioles often ciliate; Mountain and Pacific states. | Thelypodium |
Key to Genera of Group 2
| 1 | Racemes bracteate throughout | > 2 |
| 1 | Racemes ebracteate or proximalmost flowers bracteate | > 6 |
| 2 | Perennials; leaf blade margins entire. | Aphragmus |
| 2 | Annuals; leaf blade margins pinnately lobed, sinuate, or dentate | > 3 |
| 3 | Plants pubescent (trichomes retrorse or recurved). | Erucastrum |
| 3 | Plants glabrous | > 4 |
| 4 | Petals pink or purple; cauline leaves compound (3-5-foliolate). | Cardamine |
| 4 | Petals yellow; cauline leaves not compound | > 5 |
| 5 | Basal leaf blade margins 1 or 2 (or 3)-pinnatisect; petals 4-20 mm. | Selenia |
| 5 | Basal leaf blade margins dentate, or sinuate- to runcinate-pinnatifid; petals 1.5-2 mm. | Sisymbrium |
| 6 | Petals absent | > 7 |
| 6 | Petals present | > 8 |
| 7 | Sepals 0.7-1.2 mm; ovules 6-22 per ovary. | Cardamine |
| 7 | Sepals 1.2-3 mm; ovules 70-242 per ovary. | Rorippa |
| 8 | Flowers zygomorphic | > 9 |
| 8 | Flowers actinomorphic | > 11 |
| 9 | Ovaries and young fruits linear; ovules 10-120 per ovary; stamens in 3 pairs of unequal length. | Streptanthus |
| 9 | Ovaries and young fruits ovate, obcordate, or suborbicular; ovules 2 or 4 per ovary; stamens tetradynamous | > 10 |
| 10 | Annuals or perennials (without basal rosettes); abaxial petals 5-16 mm. | Iberis |
| 10 | Annuals (with basal rosettes); abaxial petals 0.5-1.5 mm. | Teesdalia |
| 11 | Stamens 2 or 4 | > 12 |
| 11 | Stamens 6 | > 16 |
| 12 | Stamens 2. | Lepidium |
| 12 | Stamens 4 | > 13 |
| 13 | Ovaries linear. | Cardamine |
| 13 | Ovaries not linear | > 14 |
| 14 | Ovules 10-24 per ovary. | Hornungia |
| 14 | Ovules 2 or 4 per ovary | > 15 |
| 15 | Filaments appendaged. | Teesdalia |
| 15 | Filaments not appendaged. | Lepidium |
| 16 | Ovaries ovate, ovoid, obovate, orbicular, globose, oblong, or elliptic (sometimes in 2 segments with such shapes) | > 17 |
| 16 | Ovaries usually linear, rarely narrowly lanceolate | > 27 |
| 17 | Petals (15-)17-25(-30) mm, usually purple or lavender, rarely white; styles and gynophores well-developed. | Lunaria |
| 17 | Petals 0.5-12(-15) mm, usually yellow, cream, or white, rarely lavender; styles and gynophores often absent | > 18 |
| 18 | Ovules 24-80 per ovary. | Rorippa |
| 18 | Ovules 1-12(-14) per ovary | > 19 |
| 19 | Ovaries and young fruits 2-segmented | > 20 |
| 19 | Ovaries and young fruits unsegmented | > 23 |
| 20 | Petals cream or pale yellow with dark purple or brown veins; ovules 4-6 per ovary. | Carrichtera |
| 20 | Petals white, lavender, or yellow, without dark veins; ovules 1 or 2(-4) per ovary | > 21 |
| 21 | Plants hispid proximally, not succulent; style distinct; petals yellow; disturbed habitats, waste places, roadsides. | Rapistrum |
| 21 | Plants glabrous throughout, succulent; style absent; petals white, lavender, or pale yellow; coastal sandy beaches | > 22 |
| 22 | Cauline leaves to 10 cm; filaments not toothed or winged. | Cakile |
| 22 | Cauline leaves 10-40 cm; filaments toothed and winged. | Crambe |
| 23 | Ovules 1 or 2(-4) per ovary | > 24 |
| 23 | Ovules 6-14 per ovary | > 25 |
| 24 | Ovules 2(-4) per ovary; young fruits angustiseptate. | Lepidium |
| 24 | Ovules 1 per ovary; young fruits latiseptate. | Thysanocarpus |
| 25 | Perennials with fleshy roots; stems 5-12(-20) dm; basal leaf blades 10-60 cm; racemes corymbose-paniculate. | Armoracia |
| 25 | Annuals, biennials, or perennials without fleshy roots; stems 0.1-3(-5) dm; basal leaf blades 1-10 cm; racemes subumbellate or corymbose | > 26 |
| 26 | Racemes bracteate basally; petals with dark veins. | Aphragmus |
| 26 | Racemes ebracteate; petals without darker veins. | Cochlearia |
| 27 | Cauline leaves compound | > 28 |
| 27 | Cauline leaves simple (sometimes divided, blade continuous between lobes) | > 29 |
| 28 | Plants terrestrial, not rooting from proximal stem nodes. | Cardamine |
| 28 | Plants aquatic, rooting from proximal stem nodes. | Nasturtium |
| 29 | Petal blades pinnately lobed. | Dryopetalon |
| 29 | Petal blades entire | > 30 |
| 30 | Plants with glandular papillae. | Chorispora |
| 30 | Plants without glandular papillae | > 31 |
| 31 | Stamens equal or subequal in length (well-exserted) | > 32 |
| 31 | Stamens tetradynamous or in 3 pairs of unequal length | > 36 |
| 32 | Petals yellow, claws and/or filaments usually pubescent, rarely both glabrous. | Stanleya |
| 32 | Petals white, lavender, pink, or purple, claws and filaments glabrous (except Warea carteri) | > 33 |
| 33 | Inflorescences corymbose racemes; se United States. | Warea |
| 33 | Inflorescences elongated racemes; Pacific and Mountain states, Oklahoma, Texas | > 34 |
| 34 | Petal claws dentate to sublaciniate; sepals ascending; stamens well-exserted. | Chlorocrambe |
| 34 | Petal claws entire; sepals spreading or erect; stamens (spreading) slightly exserted ( ¤) | > 35 |
| 35 | Fruits subsessile on equally broad gynophores. | Caulanthus |
| 35 | Fruits stipitate on narrower gynophores. | Thelypodium |
| 36 | Stamens in 3 pairs of unequal length ( ¤) | > 37 |
| 36 | Stamens tetradynamous | > 40 |
| 37 | Fruits terete; seeds not winged. | Caulanthus |
| 37 | Fruits slightly to distinctly latiseptate; seeds winged all around or only distally | > 38 |
| 38 | Cotyledons accumbent. | Streptanthus |
| 38 | Cotyledons incumbent | > 39 |
| 39 | Adaxial stamens with connate filaments and sterile anthers; fruit valves each with an obscure midvein. | Sibaropsis |
| 39 | Adaxial stamens with distinct filaments and fertile anthers; fruit valves each with a prominent midvein. | Streptanthella |
| 40 | Petal blades with purple or brown veins darker than rest of blade | > 41 |
| 40 | Petals blades with veins same color intensity as rest of blade | > 45 |
| 41 | Perennials, glaucous, glabrous; leaf blade margins entire or dentate | > 42 |
| 41 | Annuals, not glaucous, often pubescent; leaf blade margins pinnately lobed (¤) | > 43 |
| 42 | Stigmas prominently 2-lobed; ovules 76-210 per ovary. | Caulanthus |
| 42 | Stigmas obscurely 2-lobed; ovules 24-62 per ovary. | Hesperidanthus |
| 43 | Fruits indehiscent, corky, valvular segments rudimentary, seedless. | Raphanus |
| 43 | Fruits dehiscent, not corky, valvular segments well-developed, seeded | > 44 |
| 44 | Fruit valves 3-veined; terminal segments usually 1-6-seeded, sometimes seedless. | Coincya |
| 44 | Fruit valves 1-veined; terminal segments seedless. | Eruca |
| 45 | Cauline leaf blade margins entire | > 46 |
| 45 | Cauline leaf blade margins pinnately divided, sinuate, or dentate | > 52 |
| 46 | Plants biennial. | Boechera |
| 46 | Plants perennial (with rhizomes or caudices) | > 47 |
| 47 | Plants with slender or thick rhizomes or tubers. | Cardamine |
| 47 | Plants with caudices | > 48 |
| 48 | Petals yellow, lavender, or purple. | Hesperidanthus |
| 48 | Petals white | > 49 |
| 49 | Ovules 28-90 per ovary. | Boechera |
| 49 | Ovules 6-12(-18) per ovary | > 50 |
| 50 | Basal leaf blades ciliate, leathery. | Nevada |
| 50 | Basal leaf blades glabrous, not leathery ( ¤) | > 51 |
| 51 | Fruits latiseptate; cotyledons accumbent. | Cardamine |
| 51 | Fruits terete; cotyledons incumbent. | Eutrema |
| 52 | Petals yellow | > 53 |
| 52 | Petals white, pink, lavender, or purple | > 59 |
| 53 | Racemes bracteate basally. | Erucastrum |
| 53 | Racemes usually ebracteate or, rarely, proximalmost 1 or 2 flowers bracteate | > 54 |
| 54 | Ovaries and young fruits 2-segmented ( ¤) | > 55 |
| 54 | Ovaries and young fruits unsegmented | > 57 |
| 55 | Fruit valves 1-veined; sepals usually erect or ascending, rarely spreading. | Brassica |
| 55 | Fruit valves 3-7-veined; sepals spreading to reflexed | > 56 |
| 56 | Seeds ovoid or oblong; stigmas entire. | Hirschfeldia |
| 56 | Seeds globose; stigmas 2-lobed. | Sinapis |
| 57 | Stigmas entire. | Rorippa |
| 57 | Stigmas 2-lobed ( ¤) | > 58 |
| 58 | Seeds biseriate; fruit valves 1-veined; cotyledons conduplicate. | Diplotaxis |
| 58 | Seeds uniseriate; fruit valves 3-veined; cotyledons incumbent. | Sisymbrium |
| 59 | Ovaries and young fruits 2-segmented | > 60 |
| 59 | Ovaries and young fruits unsegmented | > 61 |
| 60 | Ovules (1 or) 2(-4) per ovary. | Cakile |
| 60 | Ovules 20-60 per ovary. | Diplotaxis |
| 61 | Cauline leaf blades reniform or cordate, margins crenate or dentate. | Alliaria |
| 61 | Cauline leaf blades usually not reniform or cordate, at least some with margins pinnatifid, pinnatisect, runcinate, or pectinate | > 62 |
| 62 | Leaf blades pectinate or pinnatisect, lateral lobes filiform to linear; racemes: rachises flexuous. | Sibara |
| 62 | Leaf blades dentate or variously divided, not pectinate, rarely pinnatisect, lobes (when present) usually ovate to oblong, rarely linear; racemes: rachises usually not flexuous (except some Cardamine) | > 63 |
| 63 | Petals usually purple, if not, then margins crisped and/or channeled. | Caulanthus |
| 63 | Petals white or lavender, margins neither crisped nor channeled | > 64 |
| 64 | Leaf blade margins pinnatisect or pinnatifid throughout ( ¤) | > 65 |
| 64 | Leaf blade margins entire or dentate ± distally ( ¤) | > 66 |
| 65 | Seeds not winged; replum flattened; fruit valves dehiscing elastically. | Cardamine |
| 65 | Seeds winged; replum rounded; fruit valves not dehiscing elastically. | Planodes |
| 66 | Fruits terete; seeds not winged; cotyledons incumbent. | Caulanthus |
| 66 | Fruits latiseptate; seeds winged; cotyledons accumbent. | Streptanthus |
Key to Genera of Group 3
| 1 | Racemes bracteate basally or throughout | > 2 |
| 1 | Racemes ebracteate or proximal flowers bracteate | > 3 |
| 2 | Annuals; leaf blade margins pinnatifid; petals yellow. | Tropidocarpum |
| 2 | Perennials; leaf blade margins usually entire or dentate, rarely lobed; petals white. | Braya |
| 3 | Plants scapose; cauline leaves absent | > 4 |
| 3 | Plants not scapose; at least 1 cauline leaf present | > 5 |
| 4 | Sepals 1.5-2.5 mm; petioles of previous years not persistent. | Draba |
| 4 | Sepals 4-5 mm; petioles of previous years persistent (stramineous). | Anelsonia |
| 5 | Cauline leaves sessile, blade bases auriculate, sagittate, or amplexicaul | > 6 |
| 5 | Cauline leaves usually petiolate, if sessile, blade bases not auriculate, sagittate, or amplexicaul | > 11 |
| 6 | Trichomes finely dendritic. | Phoenicaulis |
| 6 | Trichomes stellate, forked, simple, and dendritic (never exclusively dendritic) | > 7 |
| 7 | Trichomes stalked, stellate, rarely few simple. | Arabis |
| 7 | Trichomes of a different type or a mixture of more than one | > 8 |
| 8 | Annuals; stigmas 2-lobed; petals with purple veins darker than blades. | Caulanthus |
| 8 | Biennials or perennials; stigmas entire or subentire; petals with veins not purple, color intensity same as blades | > 9 |
| 9 | Petals usually yellow or creamy white, rarely pink; young fruits appressed to rachises. | Turritis |
| 9 | Petals white, pink, lavender, or purple; young fruits not or rarely appressed to rachises (some Boechera) ( ¤) | > 10 |
| 10 | Fruits latiseptate; cotyledons accumbent. | Boechera |
| 10 | Fruits terete; cotyledons incumbent. | Transberingia |
| 11 | Trichomes sessile, medifixed, malpighiaceous or stellate. | Erysimum |
| 11 | Trichomes stalked or simple, not medifixed, malpighiaceous, stellate, forked, or dendritic | > 12 |
| 12 | Stigmas 2-lobed (conical, connivent, decurrent) | > 13 |
| 12 | Stigmas entire (capitate) | > 17 |
| 13 | Sepals spreading to reflexed. | Nerisyrenia |
| 13 | Sepals erect (sometimes connivent) | > 14 |
| 14 | Plants often with multiseriate glands; stigmas 2-horned; petal margins crisped. | Matthiola |
| 14 | Plants without multiseriate glands; stigmas not horned; petal margins not crisped | > 15 |
| 15 | Petals (6.5-)8-10(-12) mm. | Strigosella |
| 15 | Petals (13-)15-30 mm | > 16 |
| 16 | Plants tomentose, trichomes dendritic; sepals 10-15 mm. | Matthiola |
| 16 | Plants not tomentose, trichomes simple and/or forked; sepals 5-8 mm. | Hesperis |
| 17 | Cauline leaf blade margins usually 1-3-pinnatisect, pectinate, or, rarely, pinnatifid | > 18 |
| 17 | Cauline leaf blade margins entire, dentate, sinuate, or lyrate | > 22 |
| 18 | Perennials (cespitose), woody basally; leaf blades pectinate, rigid, persisting in subsequent years as pectinate spines. | Polyctenium |
| 18 | Annuals, biennials, or perennials, not woody basally; leaf blades 1-3-pinnatisect or pinnatifid, pliable, not persisting in subsequent years as spines | > 19 |
| 19 | Petals yellow; trichomes dendritic. | Descurainia |
| 19 | Petals white; trichomes simple, 2-forked, dendritic, and, sometimes, cruciform | > 20 |
| 20 | Annuals; petals 2-3.5 mm; plants puberulent, some trichomes dendritic; California, Nevada. | Sibara |
| 20 | Biennials or perennials; petals 4-10 mm; plants pubescent, trichomes forked or cruciform; n, e, c United States, Canada, Alaska ( ¤) | > 21 |
| 21 | Fruits pubescent; cotyledons incumbent. | Sandbergia |
| 21 | Fruits glabrous; cotyledons accumbent. | Arabidopsis |
| 22 | Flowers cup-shaped; petals white with purple tips. | Pennellia |
| 22 | Flowers not cup-shaped; petals white, pink, lavender, purple, yellow, or orange | > 23 |
| 23 | Proximalmost flowers bracteate | > 24 |
| 23 | Proximalmost flowers ebracteate | > 25 |
| 24 | Basal and proximalmost cauline leaf blade margins entire. | Draba |
| 24 | Basal and proximalmost cauline leaf blade margins dentate. | Braya |
| 25 | Leaf blade margins sometimes lobed, sinuate, or lyrate | > 26 |
| 25 | Leaf blade margins entire or dentate | > 27 |
| 26 | Trichomes forked; fruits terete or latiseptate, glabrous. | Arabidopsis |
| 26 | Trichomes subdendritic; fruits terete, pubescent. | Halimolobos |
| 27 | Petals yellow. | Draba |
| 27 | Petals white, lavender, pink, or purple | > 28 |
| 28 | Ovaries and young fruits pubescent ( ¤) | > 29 |
| 28 | Ovaries and young fruits glabrous | > 30 |
| 29 | Seeds winged; cotyledons accumbent; fruits strongly flattened. | Boechera |
| 29 | Seeds not winged; cotyledons incumbent; fruits slightly flattened. | Sandbergia |
| 30 | Petals (4-)5-18 mm; seeds winged. | Boechera |
| 30 | Petals 2-4(-5 mm); seeds not winged ( ¤) | > 31 |
| 31 | Fruits latiseptate; seeds biseriate; cotyledons accumbent. | Draba |
| 31 | Fruits usually terete, rarely slightly latiseptate; seeds uniseriate; cotyledons incumbent | > 32 |
| 32 | Basal leaves often petiolate; branched trichomes 2-4-rayed, stalked; ovules (30-)40-70 per ovary. | Arabidopsis |
| 32 | Basal leaves not petiolate; branched trichomes submalpighiaceous, subsessile; ovules 20-28 per ovary. | Braya |
Key to Genera of Group 4
| 1 | Plants scapose; cauline leaves absent | > 2 |
| 1 | Plants not scapose; at least 1 cauline leaf present | > 6 |
| 2 | Ovules 4 per ovary. | Cusickiella |
| 2 | Ovules 10 or more per ovary | > 3 |
| 3 | Petals yellow or orange. | Draba |
| 3 | Petals white, lavender, rose, or purple | > 4 |
| 4 | Sepals 4-5 mm; petioles of previous years persistent (stramineous). | Anelsonia |
| 4 | Sepals 1.5-3(-3.7) mm; petioles of previous years not persistent ( ¤) | > 5 |
| 5 | Cotyledons accumbent. | Draba |
| 5 | Cotyledons incumbent. | Braya |
| 6 | Cauline leaves sessile, blade bases auriculate, sagittate, or amplexicaul | > 7 |
| 6 | Cauline leaves usually petiolate, if sessile, blade bases neither auriculate nor amplexicaul | > 11 |
| 7 | Plants perennial (caudex well-developed, woody); trichomes dendritic. | Phoenicaulis |
| 7 | Plants annual, biennial or, rarely, perennial; trichomes often mixed simple, forked, stellate, or subdendritic | > 8 |
| 8 | Petals white; at least some branched trichomes sessile, stellate. | Capsella |
| 8 | Petals usually yellow, rarely creamy white or white with yellow claws; branched trichomes stalked, not stellate | > 9 |
| 9 | Styles 0.5-0.9 mm; petals 2-2.5 mm; ovules 2-4 per ovary. | Neslia |
| 9 | Styles 1-3 mm; petals (2.5-)4-12 mm; ovules 4-32(-40) per ovary | > 10 |
| 10 | Stamens in 3 pairs of unequal length; nectar glands distinct (4); fruit valves extending into stylar area. | Camelina |
| 10 | Stamens tetradynamous; nectar glands confluent; fruit valves not extending into stylar area. | Paysonia |
| 11 | Racemes bracteate throughout. | Tropidocarpum |
| 11 | Racemes ebracteate or proximalmost flowers bracteate | > 12 |
| 12 | Plants with multicellular glandular tubercles or papillae. | Bunias |
| 12 | Plants without multicellular glandular tubercles or papillae | > 13 |
| 13 | Petal apices strongly 2-fid. | Berteroa |
| 13 | Petal apices rounded, retuse, or emarginate | > 14 |
| 14 | Cauline leaf blade trichomes exclusively malpighiaceous | > 15 |
| 14 | Cauline leaf blade trichomes not exclusively malpighiaceous | > 16 |
| 15 | Petals yellow; ovules 14-18 per ovary. | Draba |
| 15 | Petals white or purplish violet; ovules 2 per ovary. | Lobularia |
| 16 | Some filaments winged, dentate, or appendaged | > 17 |
| 16 | All filaments not winged, dentate, or appendaged | > 19 |
| 17 | Plants annual or, rarely, perennial; ovules 1 or 2 per ovary. | Alyssum |
| 17 | Plants perennial; ovules 4-40 per ovary | > 18 |
| 18 | Petals yellow, 3-6 mm. | Aurinia |
| 18 | Petals usually purple to violet, rarely white, (10-)15-28 mm. | Aubrieta |
| 19 | Ovules 1 or 2 per ovary | > 20 |
| 19 | Ovules 4-100 per ovary | > 24 |
| 20 | Ovaries and young fruits angustiseptate, suborbicular, didymous; petals (3.5-)4-15 mm | > 21 |
| 20 | Ovaries and young fruits latiseptate (subterete or 4-angled), orbicular to obovate or ovoid, not didymous; petals 0.9-3(-4) mm | > 22 |
| 21 | Sepals spreading or reflexed; stigmas conical, 2-lobed; petals 3.5-10 (-12) mm. | Dimorphocarpa |
| 21 | Sepals erect, connivent; stigmas capitate, entire; petals (10-)12-15 mm. | Dithyrea |
| 22 | Ovaries and young fruits ovoid, subterete or 4-angled; petals 0.9-1.3 mm. | Euclidium |
| 22 | Ovaries and young fruits orbicular to obovate, latiseptate; petals 1.5-3(-4) mm | > 23 |
| 23 | Sepals persistent; fruiting pedicels divaricate to ascending. | Alyssum |
| 23 | Sepals caducous; fruiting pedicels reflexed. | Athysanus |
| 24 | Sepals erect, linear to oblong-linear, connivent; petals linear-oblanceolate to linear, twisted with age. | Lyrocarpa |
| 24 | Sepals erect to spreading, oblong to ovate, not connivent; petals obovate, spatulate, oblong, or oblanceolate, not twisted with age | > 25 |
| 25 | Cauline leaf blade margins 1-3-pinnatisect, pectinate, pinnatifid, or palmately 3-7-lobed | > 26 |
| 25 | Cauline leaf blade margins usually entire or dentate, rarely sinuate | > 29 |
| 26 | Leaf blades pectinate, rigid, persisting as pectinate spines. | Polyctenium |
| 26 | Leaf blades 1-3-pinnatisect, pinnatifid, or palmately 3-7-lobed, not rigid, not persisting as spines | > 27 |
| 27 | Perennials (caudex well-developed). | Smelowskia |
| 27 | Annuals | > 28 |
| 28 | Petals yellow; most or all trichomes dendritic. | Descurainia |
| 28 | Petals white; trichomes simple or forked. | Hornungia |
| 29 | Trichomes stellate or lepidote, webbed or not. | Physaria |
| 29 | Trichomes simple, forked, cruciform, pectinate, dendritic, or malpighiaceous, often mixed (never exclusively stellate or lepidote) | > 30 |
| 30 | Ovaries and young fruits strongly angustiseptate | > 31 |
| 30 | Ovaries and young fruits latiseptate (terete or 4-angled, except Hornungia) | > 32 |
| 31 | Petals 1.5-2.5 × 0.7-1.2 mm, claws indistinct; styles 0.3-0.8 (-1) mm; anthers oblong, 0.7-1 mm. | Halimolobos |
| 31 | Petals (7-)8-11(-13) × (5-)6-9 mm, claws distinct; styles 2-5 mm; anthers linear, 2.5-4 mm. | Synthlipsis |
| 32 | Plants annuals | > 33 |
| 32 | Plants perennials | > 35 |
| 33 | Racemes secund; fruiting pedicels reflexed. | Athysanus |
| 33 | Racemes not secund; fruiting pedicels erect or ascending to spreading or divaricate | > 34 |
| 34 | Petals usually yellow, (1.2-)1.5-8.5 mm (if white, late-season flowers often cleistogamous and apetalous). | Draba |
| 34 | Petals white, 0.6-1.2 mm. | Hornungia |
| 35 | Basal leaf blade margins often apically 3-5-lobed, surfaces densely silvery villous, trichomes simple or densely grayish tomentose (mostly dendritic and simple). | Smelowskia |
| 35 | Basal leaf blade margins not apically 3-5-lobed, surfaces glabrate or sparsely to densely pubescent, trichomes seldom silvery or grayish ( ¤) | > 36 |
| 36 | Cotyledons accumbent. | Draba |
| 36 | Cotyledons incumbent | > 37 |
| 37 | Fruits 4-angled; ovules 4 per ovary. | Cusickiella |
| 37 | Fruits terete; ovules 10-30 per ovary. | Braya |
Key to Genera Based Primarily on Fruiting Specimens
| 1 | Fruits silicles (lengths less than 3 times widths) | > 2 |
| 1 | Fruits siliques (at least 3 times as long as wide) | > 3 |
| 2 | Trichomes simple or absent | Group 5 |
| 2 | Trichomes (at least some) branched | Group 6 |
| 3 | Trichomes (at least some) branched | Group 7 |
| 3 | Trichomes simple or absent | Group 8 |
Key to Genera of Group 5
| 1 | Fruits 2-segmented | > 2 |
| 1 | Fruits unsegmented | > 5 |
| 2 | Fruits corky; plants glabrous; strand and seashore beaches | > 3 |
| 2 | Fruits not corky; plants pubescent; inland | > 4 |
| 3 | Fruits with well-developed proximal segments, usually seeded, terminal segments ovoid to lanceolate; cotyledons usually accumbent, sometimes incumbent. | Cakile |
| 3 | Fruits with stalklike proximal segments, seedless, terminal segments globose; cotyledons conduplicate. | Crambe |
| 4 | Cauline leaf blade margins 1- or 2-pinnatisect; fruiting pedicels strongly recurved;fruit terminal segments flattened, cochleariform, or short-lingulate, seedless. | Carrichtera |
| 4 | Cauline leaf blade margins dentate; fruiting pedicels erect to ascending (straight); fruit terminal segments globose or ovoid, 1(-3)-seeded. | Rapistrum |
| 5 | Fruits angustiseptate | > 6 |
| 5 | Fruits terete or latiseptate | > 16 |
| 6 | Cauline leaves usually petiolate, if sessile, blade bases not auriculate, sagittate, or amplexicaul | > 7 |
| 6 | Cauline leaves sessile, blade bases auriculate, sagittate, or amplexicaul | > 11 |
| 7 | Seeds 8-24 per fruit | > 8 |
| 7 | Seeds 2(-4) per fruit | > 9 |
| 8 | Perennials, 5-12(-20) dm, roots fleshy. | Armoracia |
| 8 | Annuals, 0.2-3 dm, roots not fleshy. | Hornungia |
| 9 | Racemes not or slightly elongated in fruit; seeds winged. | Iberis |
| 9 | Racemes elongated in fruit; seeds not winged | > 10 |
| 10 | Seeds 4 per fruit; cotyledons accumbent. | Teesdalia |
| 10 | Seeds 2 per fruit; cotyledons incumbent, rarely accumbent. | Lepidium |
| 11 | Fruits indehiscent, samaroid, 1-seeded. | Isatis |
| 11 | Fruits dehiscent, not samaroid, 2-16-seeded | > 12 |
| 12 | Seeds usually 2 per fruit. | Lepidium |
| 12 | Seeds 4-16 per fruit | > 13 |
| 13 | Fruits not keeled, not winged, strongly reticulate; seeds biseriate. | Cochlearia |
| 13 | Fruits keeled, winged, not reticulate; seeds uniseriate | > 14 |
| 14 | Seeds blackish brown, concentrically striate or alveolate; plants fetid. | Thlaspi |
| 14 | Seeds yellow-brown or brown, usually smooth, rarely minutely reticulate; plants not fetid | > 15 |
| 15 | Annuals; styles 0-0.3 mm. | Microthlaspi |
| 15 | Perennials or, rarely, biennials; styles (0.2-)0.4-4 mm. | Noccaea |
| 16 | Cauline leaves absent | > 17 |
| 16 | Cauline leaves present | > 20 |
| 17 | Fruits solitary on pedicles from basal rosette; seeds winged | > 18 |
| 17 | Fruits racemes, corymbose; seeds not winged | > 19 |
| 18 | Fruits oblong to globose; styles 0.7-7 mm; seeds uniseriate; se United States, s Missouri, e Texas. | Leavenworthia |
| 18 | Fruits orbicular or orbicular-ovate; styles 0.3-0.8 mm; seeds biseriate; British Columbia, Pacific and some Mountain states. | Idahoa |
| 19 | Annuals, aquatic, without multicellular glandular papillae; basal leaf blades linear or subulate. | Subularia |
| 19 | Perennials, terrestrial, with multicellular glandular papillae; basal leaf blades obovate to broadly spatulate. | Parrya |
| 20 | Racemes bracteate throughout, if only basally bracteate, then septums absent | > 21 |
| 20 | Racemes ebracteate | > 22 |
| 21 | Perennials; basal leaf blade margins entire; septums absent; styles 0.2-1 mm; seeds not winged. | Aphragmus |
| 21 | Annuals; basal leaf blade margins 1 or 2 (or 3)-pinnatisect; septums present; styles 1-12 mm; seeds winged. | Selenia |
| 22 | Fruits 30-45(-50) mm; gynophores 7-18 mm. | Lunaria |
| 22 | Fruits 1-15 mm; gynophores 0-0.5 mm | > 23 |
| 23 | Fruits dehiscent, seeds 8-90 per fruit | > 24 |
| 23 | Fruits indehiscent, seeds 1 or 2(-4) per fruit | > 25 |
| 24 | Fruit valves each with an obscure midvein; seeds 18-90 per fruit; petals yellow. | Rorippa |
| 24 | Fruit valves each with a distinct midvein; seeds 8-14 per fruit; petals white. | Cochlearia |
| 25 | Fruits strongly latiseptate, winged, with radiating rays. | Thysanocarpus |
| 25 | Fruits terete, not winged, without radiating rays | > 26 |
| 26 | Perennials (rhizomatous), hirsute; fruits globose to obovoid. | Lepidium |
| 26 | Annuals, glabrous; fruits ovoid to ellipsoid or obpyriform to clavate-obcordiform | > 27 |
| 27 | Fruits ovoid to ellipsoid; styles obsolete. | Calepina |
| 27 | Fruits obpyriform to clavate-obcordate; styles (0.8-)1.2-2 mm. | Myagrum |
Key to Genera of Group 6
| 1 | Plants scapose; cauline leaves absent | > 2 |
| 1 | Plants not scapose; at least 1 cauline leaf present | > 5 |
| 2 | Seeds 4 per fruit. | Cusickiella |
| 2 | Seeds 10 or more per fruit | > 3 |
| 3 | Seeds silvery papillate; fruit valves each with distinct (anastomosing) lateral veins. | Anelsonia |
| 3 | Seeds minutely reticulate; fruit valves each with obscure lateral veins | > 4 |
| 4 | Seeds biseriate; cotyledons accumbent. | Draba |
| 4 | Seeds usually uniseriate, rarely biseriate; cotyledons incumbent. | Braya |
| 5 | Cauline leaves sessile, blade bases auriculate, sagittate, or amplexicaul | > 6 |
| 5 | Cauline leaves usually petiolate, if sessile, blade bases not auriculate, sagittate, or amplexicaul | > 9 |
| 6 | Fruits indehiscent, 1-seeded, lenticular or compressed-globose; valves woody. | Neslia |
| 6 | Fruits dehiscent, 4-40-seeded, not lenticular or compressed-globose; valves papery or leathery | > 7 |
| 7 | Fruits obdeltoid to obdeltoid-cordiform, strongly angustiseptate; styles 0.2-0.7 mm; stellate trichomes sessile. | Capsella |
| 7 | Fruits globose, pyriform, obovoid, orbicular, or subovate, usually latiseptate, rarely angustiseptate (some Paysonia); styles 1-3.5 mm; stellate trichomes absent or short-stalked | > 8 |
| 8 | Fruit valves with caudate apex extending 1-2.5 mm onto style; cotyledons incumbent. | Camelina |
| 8 | Fruit valves not extending onto style; cotyledons accumbent. | Paysonia |
| 9 | Fruits angustiseptate | > 10 |
| 9 | Fruits latiseptate (terete or 4-angled) | > 19 |
| 10 | Racemes bracteate throughout. | Tropidocarpum |
| 10 | Racemes usually ebracteate, rarely proximalmost flowers bracteate | > 11 |
| 11 | Seeds 2 per fruit; fruits didymous, breaking into 1-seeded segments; valves indurate around margin | > 12 |
| 11 | Seeds 4-100 per fruit; fruits not didymous or, if didymous (some Physaria), inflated and not breaking into 1-seeded segments; valves not indurate around margin | > 13 |
| 12 | Stigmas conical, 2-lobed (decurrent); sepals spreading to reflexed. | Dimorphocarpa |
| 12 | Stigmas capitate, entire; sepals erect. | Dithyrea |
| 13 | Leaf blades pectinate, persisting as pectinate spines. | Polyctenium |
| 13 | Leaf blades entire or divided, neither pectinate nor persisting as spines | > 14 |
| 14 | Fruits obcordiform to panduriform; stigmas prominently 2-lobed. | Lyrocarpa |
| 14 | Fruits not obcordiform or panduriform; stigmas entire or subentire | > 15 |
| 15 | Leaf blade margins palmately (3 or) 5 (or 7)-lobed; sepals persistent. | Smelowskia |
| 15 | Leaf blade margins entire, dentate, sinuate, or pinnatisect; sepals caducous | > 16 |
| 16 | Annuals or biennials; styles 0-0.8(-1) mm; cotyledons incumbent | > 17 |
| 16 | Perennials or, rarely, annuals; styles 1.8-7 mm; cotyledons accumbent | > 18 |
| 17 | Fruits 10-24-seeded; valves glabrous. | Hornungia |
| 17 | Fruits (60-)70-100-seeded; valves pubescent. | Halimolobos |
| 18 | Cauline leaf blade margins entire; trichomes stellate. | Physaria |
| 18 | Cauline leaf blade margins sinuate or dentate; trichomes dendritic mixed with simple and forked ones. | Synthlipsis |
| 19 | Racemes secund; fruits reflexed. | Athysanus |
| 19 | Racemes not secund; fruits not reflexed | > 20 |
| 20 | Plants with multicellular glandular papillae or tubercles; fruits woody, indehiscent; cotyledons spirolobal. | Bunias |
| 20 | Plants without multicellular glandular papillae or tubercles; fruits not woody, mostly dehiscent (except Euclidium); cotyledons incumbent or accumbent | > 21 |
| 21 | Cauline leaf blade margins 1- or 2-pinnatifid or pinnatisect | > 22 |
| 21 | Cauline leaf blade margins entire, crenate, dentate, or sinuate | > 23 |
| 22 | Annuals or biennials; petals yellow. | Descurainia |
| 22 | Perennials (cespitose); petals white, lavender, or purple. | Smelowskia |
| 23 | Seeds 1 or 2 per fruit | > 24 |
| 23 | Seeds 4 or more per fruit | > 26 |
| 24 | Fruits indehiscent, subterete or 4-angled. | Euclidium |
| 24 | Fruits dehiscent, latiseptate | > 25 |
| 25 | Trichomes stellate (when branched). | Alyssum |
| 25 | Trichomes malpighiaceous. | Lobularia |
| 26 | Seeds winged or margined; filaments winged, toothed, or appendaged | > 27 |
| 26 | Seeds usually neither winged nor margined, if narrowly margined (some Physaria), trichomes exclusively stellate; filaments not winged, toothed, or appendaged | > 28 |
| 27 | Perennials; cotyledons incumbent; petals emarginate. | Aurinia |
| 27 | Annuals or biennials; cotyledons accumbent; petals deeply 2-fid. | Berteroa |
| 28 | Trichomes almost exclusively stellate (rays simple or divided, webbed or not), sometimes lepidote; septums often with apical midvein. | Physaria |
| 28 | Trichomes often mixed, not exclusively stellate, webbed, or lepidote; septums without apical midvein | > 29 |
| 29 | Cotyledons accumbent. | Draba |
| 29 | Cotyledons incumbent | > 30 |
| 30 | Seeds 10-30 per fruit, biseriate or uniseriate; plants not white-canescent. | Braya |
| 30 | Seeds 4 per fruit, not in rows; plants white-canescent throughout. | Smelowskia |
Key to Genera of Group 7
| 1 | Plants scapose; cauline leaves absent | > 2 |
| 1 | Plants not scapose; at least 1 cauline leaf present | > 3 |
| 2 | Seeds minutely reticulate; fruit valves each with obscure lateral veins. | Draba |
| 2 | Seeds silvery papillate; fruit valves each with distinct (anastomosing) lateral veins. | Anelsonia |
| 3 | Cauline leaves sessile, blade bases auriculate, sagittate, or amplexicaul | > 4 |
| 3 | Cauline leaves petiolate, if sessile, blade bases not auriculate, sagittate, or amplexicaul | > 9 |
| 4 | Fruits latiseptate; cotyledons accumbent | > 5 |
| 4 | Fruits terete, or 4-angled; cotyledons usually incumbent, rarely accumbent (Turritis) | > 7 |
| 5 | Plants tomentose, trichomes finely dendritic; seeds (6-)8-16(-18) per fruit. | Phoenicaulis |
| 5 | Plants pubescent, trichomes usually stellate, forked, or 2-14-rayed; (if trichomes dendritic) seeds more than 24 per fruit | > 6 |
| 6 | Branched trichomes stellate, 3-5-rayed; fruits straight, erect (appressed to rachises) to divaricate, 0.6-2 mm wide. | Arabis |
| 6 | Branched trichomes forked, 2-14-rayed, or dendritic; fruits arcuate, curved, or straight, usually reflexed, pendent, or spreading, rarely erect, 1-6 mm wide. | Boechera |
| 7 | Seeds uniseriate; stigmas 2-lobed; branched trichomes 2-rayed. | Caulanthus |
| 7 | Seeds biseriate; stigmas entire; branched trichomes dendritic or substellate | > 8 |
| 8 | Fruiting pedicels divaricate to ascending; fruits terete, not appressed to rachises. | Transberingia |
| 8 | Fruiting pedicels erect; fruits subterete or 4-angled, appressed to rachises. | Turritis |
| 9 | Racemes bracteate throughout | > 10 |
| 9 | Racemes ebracteate or only proximalmost flowers bracteate | > 11 |
| 10 | Plants annual; fruits angustiseptate; petals yellow. | Tropidocarpum |
| 10 | Plants perennial; fruits terete; petals white, pink, or purple. | Braya |
| 11 | Trichomes sessile, malpighiaceous, sometimes mixed with sessile 3-5-rayed, stellate ones (simple trichomes absent). | Erysimum |
| 11 | Trichomes stalked, cruciform, dendritic, stellate, submalpighiaceous, or forked (simple trichomes sometimes present) | > 12 |
| 12 | Stigmas conical, 2-lobed, lobes connivent, often decurrent | > 13 |
| 12 | Stigmas capitate, usually entire, rarely slightly 2-lobed, lobes neither connivent nor decurrent | > 16 |
| 13 | Seeds winged; cotyledons accumbent; stigmas usually with 2 horns (if not, fruits (4-)6-12(-15) cm). | Matthiola |
| 13 | Seeds not winged; cotyledons incumbent; stigmas without horns | > 14 |
| 14 | Fruits torulose, glabrous; trichomes simple and forked; glandular (glands unicellular, on uniseriate stalks). | Hesperis |
| 14 | Fruits not torulose, pubescent; some trichomes dendritic; not glandular | > 15 |
| 15 | Annuals; fruits 4-angled; sepals erect; styles obsolete. | Strigosella |
| 15 | Perennials or subshrubs; fruits angustiseptate or terete; sepals spreading; styles 0.9-4.3 mm. | Nerisyrenia |
| 16 | Cauline leaf blade margins usually pectinate, pinnatifid, or pinnatisect, rarely lyrate | > 17 |
| 16 | Cauline leaf blade margins usually entire or dentate, rarely sinuate | > 23 |
| 17 | Fruits latiseptate | > 18 |
| 17 | Fruits terete, 4-angled, or angustiseptate | > 20 |
| 18 | Fruits strongly torulose; cotyledons incumbent. | Sandbergia |
| 18 | Fruits not torulose; cotyledons accumbent | > 19 |
| 19 | Biennials or perennials; branched trichomes forked and 3-rayed, stellate. | Arabidopsis |
| 19 | Annuals; at least some branched trichomes dendritic. | Sibara |
| 20 | Leaf blades pectinate, rigid; fruits slightly angustiseptate. | Polyctenium |
| 20 | Leaf blades pinnatifid or pinnatisect, not rigid; fruits terete or 4-angled | > 21 |
| 21 | Branched trichomes submalpighiaceous or 2-forked. | Braya |
| 21 | Branched trichomes mostly dendritic | > 22 |
| 22 | Annuals, biennials, or, rarely, perennials (without caudex); seeds mucilaginous when wetted; petals yellow. | Descurainia |
| 22 | Perennials (caudex well-developed); seeds not mucilaginous when wetted; petals white, lavender, or pink. | Smelowskia |
| 23 | Seeds winged | > 24 |
| 23 | Seeds not winged | > 25 |
| 24 | Fruiting racemes usually not secund; styles distinct; flowers not cup-shaped; fruiting pedicels reflexed, pendent, erect, or divaricate. | Boechera |
| 24 | Fruiting racemes secund; styles obsolete; flowers cup-shaped; fruiting pedicels divaricate-ascending. | Pennellia |
| 25 | Seeds biseriate | > 26 |
| 25 | Seeds uniseriate | > 29 |
| 26 | Fruiting pedicels pendent | > 27 |
| 26 | Fruiting pedicels erect, ascending, or spreading | > 28 |
| 27 | Cotyledons accumbent; seeds 8-90 per fruit. | Boechera |
| 27 | Cotyledons incumbent; seeds 150-250 per fruit. | Pennellia |
| 28 | Styles 4-6 mm; fruits pubescent, trichomes setiform mixed with smaller, stellate ones. | Aubrieta |
| 28 | Styles to 2 mm; fruits glabrous or pubescent, trichomes 2- or 4-rayed, not setiform. | Draba |
| 29 | Cotyledons accumbent; fruits latiseptate | > 30 |
| 29 | Cotyledons incumbent; fruits terete or 4-angled | > 31 |
| 30 | Basal leaf margins entire; seeds 14-22(-30) per fruit. | Boechera |
| 30 | Basal leaf margins coarsely dentate; seeds 24-48 per fruit. | Arabidopsis |
| 31 | Fruits ellipsoid to oblong; seeds 4-8 per fruit. | Smelowskia |
| 31 | Fruits linear; seeds (16-)20-140 per fruit | > 32 |
| 32 | Fruits pubescent, trichomes subsessile, with coarser, stalked ones; cauline leaf blade margins dentate to sinuate. | Halimolobos |
| 32 | Fruits glabrous or pubescent, trichomes dendritic, forked, cruciform, stellate, or submalpighiaceous (not mixed); cauline leaf blade margins usually entire, rarely dentate | > 33 |
| 33 | Seeds 90-140 per fruit; trichomes dendritic. | Pennellia |
| 33 | Seeds 20-70 per fruit; trichomes forked, cruciform, stellate, or submalpighiaceous | > 34 |
| 34 | Trichomes submalpighiaceous. | Braya |
| 34 | Trichomes forked, cruciform, or stellate | > 35 |
| 35 | Fruits densely pubescent; seedss 20-30 per fruit. | Sandbergia |
| 35 | Fruits glabrous; seeds 30-70 per fruit. | Arabidopsis |
Key to Genera of Group 8
| 1 | Plants scapose; cauline leaves absent | > 2 |
| 1 | Plants not scapose; at least 1 cauline leaf present | > 5 |
| 2 | Fruits (some or all) on solitary pedicels (from basal rosettes); seeds winged or margined. | Leavenworthia |
| 2 | Fruits in corymbs or racemes; seeds not winged, not margined | > 3 |
| 3 | Annuals or, rarely, perennials; cotyledons conduplicate; seeds 20-36 per fruit; petals yellow. | Diplotaxis |
| 3 | Perennials (cespitose); cotyledons accumbent; seeds 8-20 per fruit; petals white, lavender, or purple | > 4 |
| 4 | Stigmas entire; plants eglandular. | Cardamine |
| 4 | Stigmas lobed (lobes prominent, decurrent); plants with multicellular glandular papillae or tubercles (except Parrya arctica). | Parrya |
| 5 | Fruits indehiscent or breaking into 1-seeded segments | > 6 |
| 5 | Fruits dehiscent, more than 1-seeded | > 9 |
| 6 | Plants with multicellular glandular papillae or tubercles. | Chorispora |
| 6 | Plants eglandular | > 7 |
| 7 | Fruits not segmented, 1-seeded (samaroid). | Isatis |
| 7 | Fruits segmented, usually more than 1-seeded | > 8 |
| 8 | Styles obsolete; cotyledons accumbent; petal veins not darker than rest of blade; plants glabrous; beaches and strands. | Cakile |
| 8 | Styles 1-5 mm; cotyledons conduplicate; petal veins darker than rest of blade; plants pubescent; inland. | Raphanus |
| 9 | Fruits usually segmented, if unsegmented (Orychophragmus), stigma lobes decurrent and petiole bases strongly auriculate; cotyledons conduplicate | > 10 |
| 9 | Fruits unsegmented; cotyledons incumbent or accumbent | > 18 |
| 10 | Cauline leaf blade bases auriculate to amplexicaul | > 11 |
| 10 | Cauline leaf blade bases neither auriculate nor amplexicaul | > 12 |
| 11 | Fruits segmented; stigmas entire or lobes not decurrent; seeds globose. | Brassica |
| 11 | Fruits unsegmented; stigmas lobed, lobes decurrent; seeds oblong. | Orychophragmus |
| 12 | Seeds biseriate | > 13 |
| 12 | Seeds uniseriate | > 14 |
| 13 | Terminal fruit segments beaklike, not ensiform; petals veins same color as blade. | Diplotaxis |
| 13 | Terminal fruit segments ensiform; petal veins darker than rest of blade. | Eruca |
| 14 | Fruit valves each prominently 3-7-veined | > 15 |
| 14 | Fruit valves each obscurely veined or midvein prominent | > 16 |
| 15 | Fruits (30-)40-150-seeded; sepals erect. | Coincya |
| 15 | Fruits 4-16(-24)-seeded; sepals spreading or reflexed. | Sinapis |
| 16 | Racemes bracteate throughout or at least basally. | Erucastrum |
| 16 | Racemes ebracteate | > 17 |
| 17 | Fruit valves each prominently 1-veined; fruits divaricate to erect, if appressed to rachises, terminal segments seedless. | Brassica |
| 17 | Fruit valves obscurely 3-7-veined; fruits erect, appressed to rachises, terminal segments 1- or 2-seeded. | Hirschfeldia |
| 18 | Fruits latiseptate | > 19 |
| 18 | Fruits terete or 4-angled | > 33 |
| 19 | Replums strongly flattened; fruit valves dehiscing elastically, becoming spirally or circinately coiled. | Cardamine |
| 19 | Replums terete; fruit valves neither dehiscing elastically nor coiled | > 20 |
| 20 | Seeds winged at least distally | > 21 |
| 20 | Seeds not winged | > 27 |
| 21 | Cotyledons incumbent | > 22 |
| 21 | Cotyledons accumbent | > 23 |
| 22 | Fruits erect; cauline leaf blade margins entire. | Sibaropsis |
| 22 | Fruits reflexed; cauline leaf blade margins dentate or pinnatifid. | Streptanthella |
| 23 | Cauline leaf blade margins pinnatifid to pinnatisect into dentate lobes. | Planodes |
| 23 | Cauline leaf blade margins sometimes entire or dentate | > 24 |
| 24 | Stigmas usually prominently 2-lobed, if entire, stamens in 3 pairs of unequal length and/or calyces urceolate. | Streptanthus |
| 24 | Stigmas entire, stamens tetradynamous, calyces not urceolate | > 25 |
| 25 | Cauline leaf blade bases not auriculate or sagittate. | Boechera |
| 25 | Cauline leaf blade bases auriculate or sagittate | > 26 |
| 26 | Seeds 10-28 per fruit; fruits 6-11.7 cm. | Boechera |
| 26 | Seeds 50-86 per fruit; fruits 1.5-4.7 cm; (Texas). | Dryopetalon |
| 27 | Cauline leaf blade margins pectinate (lobes filiform). | Sibara |
| 27 | Cauline leaf blade margins not pectinate, entire, dentate, or pinnately lobed | > 28 |
| 28 | Plants tomentose; gynophores 10-20 mm. | Stanleya |
| 28 | Plants glabrous or sparsely pubescent; gynophores (0-)0.1-11 (-16 sometimes in Warea) mm | > 29 |
| 29 | Leaf blade margins dentate or pinnately lobed | > 30 |
| 29 | Leaf blade margins entire in distalmost leaves | > 31 |
| 30 | Cauline leaves sessile, blade bases auriculate or amplexicaul; petals yellow. | Barbarea |
| 30 | Cauline leaves petiolate, blade bases neither auriculate nor amplexicaul; petals white, lavender, or purple. | Thelypodium |
| 31 | Perennials; septums absent; cotyledons incumbent. | Aphragmus |
| 31 | Annuals, biennials, or, rarely, perennials; septums complete; cotyledons accumbent | > 32 |
| 32 | Gynophores 0.1-3 mm; seeds smooth or minutely reticulate; stamens in 3 pairs of unequal length; California. | Streptanthus |
| 32 | Gynophores 3-16 mm; seeds concentrically striate; stamens subequal; se United States. | Warea |
| 33 | Cauline leaves pinnately compound; stems rooting from proximal nodes. | Nasturtium |
| 33 | Cauline leaves simple, sometime pinnately lobed; stems not rooting from proximal nodes (except some Rorippa) | > 34 |
| 34 | Fruits with septums partitioned between seeds; cauline leaves with strongly auriculate petioles. | Coelophragmus |
| 34 | Fruits with septums not partitioned between seeds; cauline leaves either sessile or petioles not auriculate | > 35 |
| 35 | Cauline leaf blade bases auriculate, sagittate, or amplexicaul | > 36 |
| 35 | Cauline leaf blade bases not auriculate, sagittate, or amplexicaul | > 46 |
| 36 | Stigmas prominently 2-lobed | > 37 |
| 36 | Stigmas usually entire, rarely obscurely 2-lobed | > 38 |
| 37 | Fruits sessile or subsessile; petal margins often crisped. | Caulanthus |
| 37 | Fruits usually on gynophores (1.5-)3-9.5 mm, if gynophores shorter, styles clavate; petal margins seldom crisped. | Thelypodiopsis |
| 38 | Gynophores (6-)10-25 mm. | Stanleya |
| 38 | Gynophores 0-5 mm, if longer, petals purple | > 39 |
| 39 | Cauline leaf blade margins dentate, serrate, or pinnately lobed | > 40 |
| 39 | Cauline leaf blade margins entire or repand | > 43 |
| 40 | Seeds biseriate, colliculate or foveolate. | Rorippa |
| 40 | Seeds uniseriate, reticulate or papillate | > 41 |
| 41 | Annuals; cotyledons incumbent; petal margins often crisped. | Caulanthus |
| 41 | Biennials or perennials; cotyledons accumbent; petal margins not crisped | > 42 |
| 42 | Stems angled; petals yellow; nectar glands separate (4). | Barbarea |
| 42 | Stems not angled; petals purple, pink, or white; nectar glands confluent. | Iodanthus |
| 43 | Fruits 4-angled; seeds papillose, mucilaginous when wetted. | Conringia |
| 43 | Fruits terete; seeds reticulate, not mucilaginous when wetted | > 44 |
| 44 | Gynophores (0.5-)1-6(-8.5) mm; anthers (1-)1.5-6 mm, often coiled after dehiscence. | Thelypodium |
| 44 | Gynophores 0-0.4 mm; anthers 0.2-4 mm, not coiled after dehiscence | > 45 |
| 45 | Stigmas entire; cauline leaf blade bases sagittate- amplexicaul. | Eutrema |
| 45 | Stigmas 2-lobed; cauline leaf blade bases auriculate. | Thelypodiopsis |
| 46 | Stigmas 2-lobed | > 47 |
| 46 | Stigmas entire | > 49 |
| 47 | Fruit valves each distinctly 3-veined; petals yellow. | Sisymbrium |
| 47 | Fruit valves each with only midvein distinct; petals purple or white with purple veins | > 48 |
| 48 | Lateral sepals not saccate, median sepals not cucullate. | Caulanthus |
| 48 | Lateral sepals saccate, median sepals cucullate. | Hesperidanthus |
| 49 | Gynophores (0.5-)1.5-28 mm; anthers coiled after dehiscence | > 50 |
| 49 | Gynophores 0-1 mm; anthers not coiled after dehiscence | > 52 |
| 50 | Petals yellow, claws and/or filaments pubescent or papillate; sepals spreading to reflexed. | Stanleya |
| 50 | Petals white, lavender, or purple, claws and filaments glabrous; sepals erect or ascending | > 51 |
| 51 | Perennials; cauline leaf blades often hastate, margins entire; petal claws dentate or incised. | Chlorocrambe |
| 51 | Biennials; cauline leaf blades linear, lanceolate, or oblong, margins entire, laciniate, or dentate; petal claws entire. | Thelypodium |
| 52 | Perennials (with caudex) | > 53 |
| 52 | Annuals or, rarely, biennials | > 55 |
| 53 | Seeds usually 16-110 per fruit (as few as 8 in Hesperidanthus suffrutescens); petals usually yellow, purple, or lavender, rarely white with purple veins. | Hesperidanthus |
| 53 | Seeds 6-12(-14) per fruit; petals white without purple veins | > 54 |
| 54 | Leaf blades rigid, ciliate; fruit valves each with obscure midvein. | Nevada |
| 54 | Leaf blades not rigid, glabrous; fruit valves each with prominent midvein. | Eutrema |
| 55 | Seeds dark brown or black, longitudinally striate; fruiting pedicels as broad as fruit. | Alliaria |
| 55 | Seeds yellow or reddish brown, sculptured, not striate; fruiting pedicels usually narrower than, rarely as broad as, fruit | > 56 |
| 56 | Petals pinnatifid; filaments and petal claws papillate basally. | Dryopetalon |
| 56 | Petals entire; filaments and petal claws not papillate basally | > 57 |
| 57 | Seeds biseriate; cotyledons accumbent. | Rorippa |
| 57 | Seeds uniseriate; cotyledons incumbent. | Caulanthus |