Leaves variable, basal leaves often pinnatisect with stem leaves reducing in size and commonly toothed or entire.
Flowers in racemes, usually many-flowered, bractless, elongating in fruit. Sepals usually short, ± erect. Petals present and longer than sepals, or more often reduced or absent. Stamens 6, 4 or 2. Ovary sessile or rarely on a gynophore; stigma capitate to slightly lobed.
Silicula pedicellate, dehiscent or not, not constricted into valve and beak regions, flattened at right angles to the narrow septum, usually notched with the style either enclosed in or exserted from notch; valves strongly keeled, usually winged; seed 1 per loculus.
Lepidium howei-insulae and Lepidium nesophilum are both endemic to Lord Howe Island and are not included in the key.
| | Key to the species | |
| 1 | Fruit dehiscent | 3 |
| Fruit indehiscent, but sometimes breaking into 1-seeded units | 2 |
| 2 | Fruit pitted; leaves pinnatisect, lobes linear | Lepidium didymum |
| Fruit smooth; leaves oblanceolate, entire or almost so
Back to 1 | Lepidium draba |
| 3 | Stamens 6 | 4 |
| Stamens 2 or 4
Back to 1 | 8 |
| 4 | Stem leaves sessile, auriculate, entire to toothed, generally more than 3 mm wide, scattered | 5 |
| Stem leaves more or less linear, entire, not auriculate, mostly less than 2 mm wide, often clustered
Back to 3 | 7 |
| 5 | Stem leaves more or less broad-ovate to circular, entire | Lepidium perfoliatum |
| Stem leaves more or less triangular or oblanceolate to obovate, margins usually toothed, sometimes lobed or entire
Back to 4 | 6 |
| 6 | Stems, pedicels and leaves glabrous | Lepidium foliosum |
| Stems, pedicels and leaves hairy
Back to 5 | Lepidium campestre |
| 7 | Fruiting pedicel less than 5 mm long; style more or less shorter than apical notch of silicula; stem warty or shortly papillose | Lepidium phlebopetalum |
| Fruiting pedicel more than 5 mm long; style longer than apical notch of silicula; stem sparsely papillose
Back to 4 | Lepidium leptopetalum |
| 8 | Stamens usually 4 | 9 |
| Stamens usually 2
Back to 3 | 13 |
| 9 | Leaves auriculate; stems distinctly hairy; silicula more or less hairy when young | 10 |
| Stem leaves attenuate at base; stems more or less glabrous or finely hairy; silicula glabrous or papillose
Back to 8 | 11 |
| 10 | Stem with obtuse hairs or papillose | Lepidium papillosum |
| Stem with acicular hairs
Back to 9 | Lepidium oxytrichum |
| 11 | Petals absent or shorter than sepals; wings at least commencing in lower half of fruit | 12 |
| Petals longer than sepals; wing formed only in upper half of fruit
Back to 9 | Lepidium virginicum |
| 12 | Fruit glabrous; wings acute, uniform around fruit | Lepidium monoplocoides |
| Fruit papillose; wings obtuse, tapering in lower half of fruit
Back to 11 | Lepidium pseudopapillosum |
| 13 | Petals longer than sepals | Lepidium virginicum |
| Petals absent or reduced and shorter than sepals
Back to 8 | 14 |
| 14 | All leaves lobed or dissected to some degree | Lepidium bonariense |
| At least upper stem leaves neither lobed nor dissected
Back to 13 | 15 |
| 15 | Leaf bases more or less auriculate | 16 |
| Leaf bases attenuate
Back to 14 | 20 |
| 16 | Inflorescence a corymb, short, not elongating in fruit | Lepidium fasciculatum |
| Inflorescence a raceme, elongating in fruit
Back to 15 | 17 |
| 17 | Pedicels glabrous | 18 |
| Pedicels hairy
Back to 16 | 19 |
| 18 | Silicula more than 3 mm long; petals rudimentary, ovate | Lepidium hypenantion |
| Silicula less than 3 mm long; petals, if present, rudimentary, linear
Back to 17 | Lepidium sagittulatum |
| 19 | Plants not spinescent; silicula more or less hairy | Lepidium hyssopifolium |
| Smaller branches spinescent; silicula glabrous
Back to 17 | Lepidium aschersonii |
| 20 | Pedicels glabrous | Lepidium pseudohyssopifolium |
| Pedicels hairy
Back to 15 | 21 |
| 21 | Pedicels more or less shorter than or equal to silicula | 22 |
| Pedicel longer than silicula
Back to 20 | Lepidium peregrinum |
| 22 | Fruit less than 3 mm long; stem glabrous or with a few scattered hairs | 23 |
| Fruit more than 3 mm long; stem with long spreading obtuse hairs
Back to 21 | Lepidium muelleri-ferdinandi |
| 23 | Marginal hairs on leaves long or absent | Lepidium africanum |
| Marginal hairs on leaves short, acute or obtuse (often visible only on young leaves)
Back to 22 | Lepidium pseudotasmanicum |
