Black mustard
Brassica nigra
A tall, wiry annual crucifer reaching two metres, with bristly, lyre-shaped lower leaves, smooth narrow upper ones, and loose spikes of small yellow four-petalled flowers. The short seed pods are held tight against the stem, which is what sets it apart from the other wild mustards. Its dark, pungent seeds are the traditional source of table mustard; young leaves and flowers are eaten too.
A plant of open, disturbed ground: arable margins, waste ground, riverbanks, shingle and coastal cliffs, on well-drained fertile soil. Long naturalised in Britain, commonest in the south and east and scarce further north.
Leaves, flowers and seed are all eaten, but the seed is strongly pungent and mustard oil can blister skin held against it, so keep any poultice brief. Large amounts of raw leaf are harsh on the stomach. Arable margins are often sprayed; pick elsewhere.
Always use more than one reference to confirm a plant. You are responsible for what you choose to forage.
Habit
A branching annual, often waist to head height and occasionally to two metres, with thin wiry stems. Bristly and rough at the base, smooth and slightly blue-green above.
Flowers
Bright yellow, four petals in a cross, around a centimetre across, carried in loose heads that lengthen into a long spike as the pods form below.
Seed pods
Short, roughly 1–2 cm, four-angled and beaked, held erect and pressed close against the stem. This is the decisive check: the other yellow wild mustards and charlocks hold their pods out at an angle.
Leaves
Lower leaves large, rough-hairy and lyre-shaped, with one big end lobe and smaller side lobes. Upper leaves are narrow, smooth and carried on a clear stalk, not wrapped around the stem as in turnip and its relatives.
Seeds
Dark reddish-brown to nearly black and about a millimetre across. Crushed and wetted they build a sharp heat over several minutes; dry seed on the tongue is almost tasteless at first.
Updated 2026-08-07T21:15:27.061Z · Part of the shared Foragers Log catalogue · Herb