Leaves usually alternate, simple to pinnate, basal leaves often pinnatisect, upper stem leaves reducing; stipules absent.
Inflorescence mostly a terminal raceme, sometimes corymbose, commonly elongating in fruit. Flowers actinomorphic, bisexual, nectariferous. Sepals 4, free, in 2 whorls. Petals 4, free, usually clawed, spreading in the form of a cross. Stamens usually 6 in 2 whorls, outer 2 filaments shorter than 4 inner; anthers dehiscing longitudinally. Gynoecium of 2 fused carpels, ovary superior, 2-locular, false septum dividing ovary typically present and persistent after seed dispersal; style single, stigma usually 2-lobed; placentation parietal, ovules 1–many.
Fruit elongated (siliqua) or short (silicula), usually dehiscent and opening from the base by 2 valves, or the fruit transversely jointed and breaking into 1-seeded units. Some fruits have an extension called a beak that may or may not be seed-bearing. The seeds are often characteristic in shape, colour and possession of the ability to form a mucilaginous film when wet. Embryo morphology may also be diagnostic.
Many species are cultivated as food plants. Some are commonly grown as ornamentals and many are weeds. Matthiola (stocks) and Cheiranthus (wallflowers) are often cultivated as ornamentals and in some instances they may have escaped. These genera (indicated by **) are keyed out but not treated further in the text. Key adapted from Hewson (1982b).
| | Key to the genera | |
| 1 | Fruit a siliqua (length, excluding beak, more than 3 times width) | 2 |
| Fruit a silicula (length, excluding beak, less than 3 times width) | 30 |
| 2 | Fruit differentiated into valve and beak | 3 |
| Fruit with valve region only (style sometimes persistent, but not developed into a beak)
Back to 1 | 9 |
| 3 | Seeds in 2 rows in each loculus | 4 |
| Seeds in 1 row in each loculus
Back to 2 | 5 |
| 4 | Petals with purple veins; stigma 2-lobed; beak flattened, 5–10 mm long | Eruca |
| Petals without purple veins; stigma capitate; beak more or less conical, c. 2 mm long
Back to 3 | Diplotaxis |
| 5 | Fruit indehiscent, mostly more than 4 mm wide, inflated or markedly constricted between seeds and breaking into 1-seeded units | Raphanus |
| Fruit dehiscent, usually less than 3 mm wide, not inflated, rarely more or less constricted between seeds and then not breaking into 1-seeded units
Back to 3 | 6 |
| 6 | Valves with only 1 prominent vein or rarely venation obscure | 7 |
| Valves with 3 or more prominent veins
Back to 5 | 8 |
| 7 | Valves angled; all leaves entire and stem-clasping | Conringia |
| Valves rounded; at least some leaves toothed or deeply lobed, or rarely some stem-clasping
Back to 6 | Brassica |
| 8 | Fruit spreading; beak cylindrical, conical or flattened | Sinapis |
| Fruit appressed to stem; beak swollen
Back to 6 | Hirschfeldia |
| 9 | Plants with simple hairs or plants glabrous | 10 |
| Plants with branched hairs
Back to 2 | 19 |
| 10 | Septum absent; fruit less than 7 mm long | Menkea |
| Septum complete; fruit more than 10 mm long
Back to 9 | 11 |
| 11 | Seeds mucilaginous when wet | 12 |
| Seeds not mucilaginous when wet
Back to 10 | 14 |
| 12 | Plants growing west of the tablelands and stamens 6; seeds finely papillose; flowers white to yellow or rarely lavender | Arabidella |
| Plants either growing on the coast and tablelands and stamens 6 or growing further west and stamens 4; seeds not papillose; flowers always white
Back to 11 | 13 |
| 13 | Basal leaves lobed or commonly more than 10 cm long; stem leaves sessile, sagittate | Rorippa |
| Basal leaves not persistent, lower stem leaves not lobed, mostly less than 8 cm long; upper stem leaves petiolate
Back to 12 | Irenepharsus |
| 14 | Flowers usually white, sometimes pink or purple | 15 |
| Flowers yellow
Back to 11 | 17 |
| 15 | Fruit valves more or less flat; dehiscence clock-spring-like; flowers white, pink or purple | Cardamine |
| Fruit valves convex; dehiscence not spring-like; flowers white
Back to 14 | 16 |
| 16 | Leaves chiefly basal and lobed or leaves pinnate | Rorippa |
| Basal leaves not persistent, stem leaves simple and toothed but not lobed
Back to 15 | Irenepharsus |
| 17 | Seeds in 2 rows per loculus | Rorippa |
| Seeds in 1 row per loculus
Back to 14 | 18 |
| 18 | Valves with 3 veins apparent; testa not reticulate | Sisymbrium |
| Valves with only midvein distinct; testa reticulate
Back to 17 | Barbarea |
| 19 | Seeds in 1 row in each loculus | 20 |
| Seeds in 2 rows in each loculus
Back to 9 | 24 |
| 20 | Petals at least 10 mm long | 21 |
| Petals less than 10 mm long
Back to 19 | 22 |
| 21 | Stigmatic lobes erect, each with dorsal swelling or horn | Matthiola |
| Stigmatic lobes spreading, without swelling or horn
Back to 20 | Cheiranthus |
| 22 | Leaves 2–3-pinnatisect; petals yellow | Descurainia |
| Leaves entire to toothed; petals white
Back to 20 | 23 |
| 23 | Midvein of fruit prominent; seeds c. 0.5 mm long; rosette usually present, leaves more or less spathulate, entire or finely toothed | Arabidopsis |
| Midvein of fruit indistinct towards apex; seeds 0.75 mm or more long; basal leaves not persistent, stem leaves more or less lanceolate to narrow-elliptic, coarsely toothed
Back to 22 | Irenepharsus |
| 24 | Fruit more than 20 mm long | 25 |
| Fruit less than 20 mm long
Back to 19 | 26 |
| 25 | Petals less than 8 mm long, yellow; plants more or less glabrous above, sparsely hairy below; basal leaves not lobed, upper leaves stem-clasping | Turritis |
| Petals more than 8 mm long, white to lavender; plants tomentose; basal leaves pinnatifid, upper leaves not stem-clasping
Back to 24 | Blennodia |
| 26 | Fruit buried in the ground | Geococcus |
| Fruit aerial, not buried
Back to 24 | 27 |
| 27 | Petals thread-like, not clawed | Stenopetalum |
| Petals obtuse, somewhat clawed
Back to 26 | 28 |
| 28 | Fruit linear, petals white | Pachymitus |
| Fruit fusiform; petals yellow or with some lavender
Back to 27 | 29 |
| 29 | Fruit densely hairy | Harmsiodoxa |
| Fruit glabrous or with a few scattered hairs
Back to 28 | Drabastrum |
| 30 | Fruit distinctly differentiated into valve region and beak | 31 |
| Fruit not distinctly differentiated into valve region and beak
Back to 1 | 33 |
| 31 | Beak flattened and spoon-like | Carrichtera |
| Beak rounded to conical
Back to 30 | 32 |
| 32 | Fruit more than 10 mm long; succulent herbs confined to seashores | Cakile |
| Fruit less than 10 mm long; not succulent, widespread weeds
Back to 31 | Rapistrum |
| 33 | Fruit with 1 seed per loculus | 34 |
| Fruit with more than 1 seed per loculus
Back to 30 | 37 |
| 34 | Fruit with a narrow septum and keeled valves | 35 |
| Fruit with a wide septum and more or less flat valves
Back to 33 | Lobularia |
| 35 | Fruit dehiscent | Lepidium |
| Fruit indehiscent but sometimes breaking into 1-seeded units
Back to 34 | 36 |
| 36 | Fruit pitted; leaves pinnatisect, lobes linear | Coronopus |
| Fruit smooth; leaves more or less oblanceolate, entire or almost so
Back to 35 | Cardaria |
| 37 | Fruit with a narrow septum; valves winged or more or less keeled | 38 |
| Fruit with a broad septum; valves neither winged nor keeled
Back to 33 | 41 |
| 38 | Fruit more or less obcordate; simple and stellate hairs present | Capsella |
| Fruit more or less globose to elliptic; plants glabrous or hairy, hairs not stellate
Back to 37 | 39 |
| 39 | Fruit c. 10 mm diam;, winged and deeply notched | Thlaspi |
| Fruit less than 5 mm diam., neither prominently winged nor markedly notched at apex
Back to 38 | 40 |
| 40 | Fruit more or less globose, less than 5 mm long; basal leaves not persistent; plants glabrous or with simple hairs only | Cuphonotus |
| Fruit ovate, more than 5 mm long; basal leaves persistent; plants hairy, all hairs bifid
Back to 39 | Phlegmatospermum |
| 41 | Fruit either more than 2 cm wide or more or less buried in the ground | 42 |
| Fruit less than 1 cm wide and aerial
Back to 37 | 43 |
| 42 | Fruit more than 2 cm wide, aerial | Lunaria |
| Fruit less than 1 cm wide, buried in the ground
Back to 41 | Geococcus |
| 43 | Septum absent | Menkea |
| Septum complete
Back to 41 | 44 |
| 44 | Petals thread-like, acute or deeply bifid | 45 |
| Petals somewhat obtuse or emarginate
Back to 43 | 46 |
| 45 | Petals entire and/or acute; basal leaves usually deeply lobed, sometimes lanceolate | Stenopetalum |
| Petals bifid; basal leaves more or less spathulate
Back to 44 | Erophila |
| 46 | Hairs stellate, appressed; staminal filaments with appendages | Alyssum |
| Hairs absent or present, if stellate not appressed; staminal filaments without appendages
Back to 44 | 47 |
| 47 | Hairs absent or all simple | Rorippa |
| Hairs present, at least some branched
Back to 46 | 48 |
| 48 | Either all leaves sessile or petiole winged; base auriculate; basal leaves not in a rosette | Camelina |
| Some or all leaves petiolate, petiole not winged; base various; basal leaves in a rosette
Back to 47 | Drabastrum |
