a	Lowermost pair of 'leaves' opposite, sessile, amplexicaul, broader than long, upper leaves alternate or subopposite, petiolate, cordate at base Cotyledons very broad, folded longitudinally and their margins deeply folded in again	Chamira
	b	Lower leaves alternate or opposite, but neither sessile, amplexicaul and broader than long, nor, if opposite, with petiolate, cordate upper leaves Cotyledons narrower, if longitudinally folded, not with margins deeply rolled in

	a	Inflorescences lateral, mostly opposite leaves	*Coronopus
	b	Inflorescences terminal or in leaf axils

	a	Fruit transversely articulate with 2 or more segments which separate at maturity Lower segment indehiscent or whole fruit breaking into 1-seeded portions
	b	Fruit not transversely articulate Siliquae or siliculae opening by valves or breaking into 1-seeded portions, or hard and indehiscent

	a	Upper segment of fruit cylindrical, oblong-ovoid or ± conical, sometimes constricted between seeds	*Raphanus
	b	Upper segment of fruit globose or ovoid, sometimes beaked

	a	Upper segment not beaked, style absent Flowers white	*Crambe
	b	Upper segment beaked, style persistent Flowers pale yellow, sometimes with red veins	*Rapistrum

	a	Fruit at least 4 times as long as broad (including length of style or beak)
	b	Fruit less than 3.5 times as long as broad

	a	Hairs simple or absent
	b	Hairs stellate, branched or a mixture of simple and branched hairs

	a	Upper stem leaves with clasping auricles
	b	Upper stem leaves without clasping auricles

	a	Upper stem leaves not divided Stems round	*Brassica
	b	Upper stem leaves divided Stems angled	*Barbarea

	a	Stem leaves pinnate, pinnatisect, trifoliolate or digitate
	b	Stem leaves simple, toothed or lobed to pinnatifid

	a	Seeds in 2 rows, rarely irregularly in 1 row Flowers white or yellow Fruit subterete, valves with inconspicuous midrib	Rorippa
	b	Seeds in 1 row Flowers white, mauve, lilac or purple

	a	Valves 1-3(-7)-nerved Leaves pinnately or sub-bipinnately partite	Heliophila
	b	Valves apparently nerveless Leaves trifoliolate or pinnate with petiolulate leaflets or leaves pinnately lobed	Cardamine

	a	Petals white, blue, lilac, pink, mauve or purple	Heliophila
	b	Petals yellow (sometimes white)

	a	Seeds in 2 rows in each locule
	b	Seeds in 1 row in each locule

	a	Beak large, flat, ensiform or lanceolate, never seed-bearing Valves hispid Flowers large, more than 15 mm long, yellow with dark veins	*Eruca
	b	Style not beak-like, 1.5-2.5 mm long, narrowly cylindrical or ± obconical, sometimes seed-bearing Flowers small, less than 9 mm long, yellow, sometimes tinged with violet when fading	*Diplotaxis

	a	Valves of fruit 1-nerved
	b	Valves of fruit 3- or more-nerved

	a	Cotyledons incumbent or longitudinally folded around the incumbent radicle Style never beak-like and seed-bearing	Sisymbrium
	b	Cotyledons always longitudinally folded around the incumbent radicle Style beak-like, often seed-bearing

	a	Fruit ± compressed or subterete, more than 2 mm wide Racemes ebracteate	*Brassica
	b	Fruit ± quadrangular, less than 2 mm wide Racemes often bracteate, at least in lower part	Erucastrum

	a	Fruit appressed, less than 1.5 mm in diam., valves 3-nerved, the nerves obscure in ripe fruit Seeds oblong to ovoid	*Hirschfeldia
	b	Fruit spreading, more than 2.5 mm in diam., valves 3-5-nerved Seeds globose	*Sinapis

	a	Plants glandular Petals longer than 10 mm Stigma deeply 2-lobed, lobes erect, each frequently with a dorsal swelling or horn	*Matthiola
	b	Plants not glandular Petals shorter than 10 mm

	a	Stem leaves amplexicaul	*Turritis
	b	Stem leaves not amplexicaul

	a	Upper stem leaves finely divided	*Descurainia
	b	Upper stem leaves simple, entire or dentate

	a	Basal leaves in a rosette Stem leaves sessile Slender, small, annual or biennial herbs up to 300 mm tall	*Arabidopsis
	b	Basal leaves not in a rosette Stem leaves petiolate Perennial herbs, up to 800 mm tall	Aplanodes

	a	Fruit angustiseptate (septum narrow because fruit is flattened at right angles to the septum)
	b	Fruit latiseptate (septum broad, fruit flattened parallel to the septum)

	a	Ovules 1-4 Cotyledons narrow, linear
	b	Ovules 6-24 Cotyledons broad, elliptic to circular

	a	Fruit indehiscent Stem leaves sagittate, amplexicaul Inflorescence a corymbose panicle	*Cardaria
	b	Fruit breaking into two 1-seeded portions or valves falling away from the seeds Stem leaves not amplexicaul Inflorescences racemes

	a	Glabrous, perennial subshrubs, virgate, erect or procumbent Leaves all entire Flowers large, petals 8-20 mm long Valves of silicula papillose to rugose	Brachycarpaea
	b	Glabrous herbs or shrublets Leaves variable Flowers small, petals 1-3 mm long Valves smooth	Lepidium

	a	Upper stem leaves cuneate Plant glabrous or sparsely puberulous with simple hairs Fruit ellipsoid to obovoid, 2-3(5) mm long	*Hymenolobus
	b	Upper stem leaves sagittate-amplexicaul Plants glabrous or with simple and branched hairs

	a	Fruit obovate-circular, 10-15 mm long, broadly winged all around, but wings broadest apically	*Thlaspi
	b	Fruit obcordate-triangular, 6-9 mm long, 4-8 mm broad, emarginate, lateral margins almost straight	*Capsella

	a	Plants with stellate, branched or medifixed hairs, sometimes mixed with simple hairs
	b	Plants with simple hairs or completely glabrous

	a	Stem leaves sagittate-amplexicaul	*Camelina
	b	Stem leaves not sagittate-amplexicaul

	a	Plants with stellate hairs Flowers yellow Petals linear-oblong, broadly clawed, densely pubescent on back Filaments each with wing-like appendage Sepals persistent whilst fruits mature	*Alyssum
	b	Plants with medifixed hairs Flowers white or pinkish Petals with a circular blade, clawed, glabrous Filaments without appendages Sepals patent	*Lobularia

	a	Annual or perennial herbs
	b	Perennial woody shrublets, glabrous

	a	Fruit a siliqua, erect Seeds in 2 rows Valves with an indistinct midrib, appearing veinless	Rorippa
	b	Fruits subcircular, compressed, discoid, pendulous, 1-seeded Valves 1-nerved	Thlaspeocarpa

	a	Petals mauve to purple Sepals 3-nerved Fruit dehiscent	Cycloptychis
	b	Petals white or pale pink Fruit indehiscent

	a	Fruit erect, valves woody, margins thickened	Silicularia
	b	Fruit pendulous, compressed, valves membranous	Schlechteria