Brassicaceae: branched biennial to 1.5m. Usually found in hedgerows and banks, typically close to habitation. The flowers are about 30mm across and reddish-purple, and sometimes white. Blooming from April-June. The seed pods are circular or ova, flattened and see through. A familiar garden plant but also widely naturalised as an escape. Native to Europe.
The seeds can be cooked, they have a pungent flavour, and are used as a mustard substitute. The pungency of mustard develops when cold water is added to the ground-up seed - an enzyme (myrosin) acts on a glycoside (sinigrin) to produce a sulphur compound. The reaction takes 10 - 15 minutes. Mixing with hot water or vinegar, or adding salt, inhibits the enzyme and produces a mild bitter mustard. The root can also be eaten raw, if used before the plant produces flowers.
Succeeds in ordinary garden soil, but prefers a light soil and partial shade but also succeeds in full sun. Sow seeds in early spring or early autumn in situ. The plant will often self-sow.