A perennial herb with a strong, sometimes divided, non-tuberous, pale tap root, and usually a single stem with a terminal rosette. The erect or decumbent stem, up to 7 cm thick, grows to 55(-140) cm, becoming woody and covered with conspicuous leaf scars, which are arranged in annual groups. The leaves of non-flowering stems are 7-18(-29) x 4-14(-25) cm, stalked, broad and rounded, with generally sinuate margins (sometimes entire or undulate); the leaves are occasionally lyrate-pinnatifid, with small basal lobes numbering 1-7(-14). The leaves on flowering stems are 10-50 x 4-25 cm, oblong, entire, sessile or up to one-third clasping, and are not broadened at the base. All leaves are glabrous and glaucous. The leaves may be dark red, blue or purple. Flowering stems usually less than ten (rarely > twenty). Inflorescences are racemes, up to 1 m long, and contain c. 10-100 flowers each (16-)2.4-3.3(-4.5) cm in diameter, normally lemon yellow in colour (less often in shades of yellow to white). Fruit normally a two-celled siliqua 5-10 cm long, cylindrical, with a short tapering beak often containing 1-2 seeds. The two fruit-cells each contain 8-16 seeds, which are angular, irregular in shape, but roughly isodiametric, finely reticulate, blackish or very dark brown, from 1.5 to 2.0 mm in diameter (1.88 + 0 04 mm, x ? S.E., n = 50), and with an air-dry weight of 2.8 mg. The plants of northern Europe belong to ssp. oleracea and those of southern Europe to ssp. robertiana. British populations show wide morphological variation, especially in leaf shape (entire to pinnatifid) and coloration (green to glaucous-silver), sinuosity of leaf margins and number of basal lobes-one to twelve or more (Mitchell 1976a). There is some inter-population variation, the populations from the north-east coast being somewhat differentiated from those on the south and west coasts, although there is not a clear-cut distinction. Plants from the north-east coast cultivated under standardized conditions in experimental gardens in Newcastle-upon-Tyne came to resemble similarlygrown plants from the south and west, which suggests that wild individuals from the north-east show a plastic adaptation to local conditions. The more westerly populations tend to contain a higher proportion of pale-flowered individuals. Most populations, if not all, are probably introduced (Mitchell 1976b); confined to maritime cliffs.