| 1 | Perennial (growing in cliffs); leaves conspicuously fleshy; petals white; silique 6-10 mm wide |
| 1' | Annual or biennial (growing on seashores or waste ground); leaves not fleshy or slightly so; petals yellow; silique up to 5 mm wide |
| 2 | Upper cauline leaves sessile or petiolate |
| 2' | Upper cauline leaves amplexicaul |
| 3 | Siliques spreading, 3.5-4 cm long; petals pale yellow |
| 3' | Siliques adpressed to rhachis, 1-1.8 cm long; petals bright yellow |
| 4 | Open flowers usually not overtopping the buds of the inflorescence; petals 11-18 mm long; basal leaves glaucous green |
| 4' | Open flowers usually overtopping the buds of the inflorescence; petals 5-12 mm long; basal leaves green |
