Black mustard (Mutarda nigra)

Black mustard is the tall annual whose tiny dark seeds gave classic European mustard its fierce heat. Most books still call it Brassica nigra; recent revisions have moved it to Rhamphospermum or Mutarda. In India it is far less grown than brown mustard, Brassica juncea, which is the kadugu and rai of most kitchens, so a tin labelled kali rai is usually dark brown juncea seed.

Botanical name: Mutarda nigra (L.) Bernh.
Family: Brassicaceae
Tamil: Karun kadugu
Hindi: Kali rai
Parts used: Seeds
Habit: Black mustard; English mustard is a shop word
Last updated: 2026-10-30

How to recognise Black mustard

It grows fast to one or two metres, much taller than brown mustard, with a branching stem that is bristly near the base.

Lower leaves are large, lobed and roughly hairy, with a big end lobe; upper leaves are small, narrow and smooth.

Small bright yellow four-petalled flowers form long loose sprays at the branch tips.

The pods are short, about one to two centimetres, and are held pressed flat against the stem, which separates it from brown mustard with its longer, spreading pods.

The seeds are very small, round and dark reddish-black, smaller than those of brown mustard.

Traditional use of Black mustard

Kitchen

Ground seed mixed with water, vinegar or wine makes prepared mustard, and whole seed is fried in oil for tempering in South Asian cooking.

European and South Asian food practice

Folk use

Mustard plasters of crushed seed on cloth were laid on the chest for colds in Europe until the mid-twentieth century.

European household practice

Modern notes on Black mustard

The heat comes from sinigrin, which an enzyme in the seed turns into sharp allyl isothiocyanate when crushed seed meets water.

Black mustard was the main seed of Dijon mustard until the twentieth century. Its pods shatter and drop seed when ripe, so farmers switched to brown mustard, which machines can harvest.

Mustard is a common food allergen and must be declared on food labels in the European Union.

Black mustard safety

Mustard plasters and seed pastes left on skin can cause blisters and burns. Eat it as a condiment in kitchen amounts.

Ecology and sourcing

It grows wild in Europe, North Africa and western Asia and has become a roadside weed in many temperate countries.

Its shattering pods let it reseed itself readily on disturbed ground.

Bees, hoverflies and butterflies visit the yellow flowers.

Related plants

Also in Brassicaceae

Questions about Black mustard

Is kali rai black mustard?

Usually not. Most dark seed sold in India is brown mustard, Brassica juncea.

How can I tell the plants apart?

Black mustard is taller and its short pods press against the stem.

Why does mustard taste hot only after crushing?

The hot compound forms only when crushed seed mixes with water.

Why is Black mustard rarely farmed now?

Its ripe pods shatter, so machine harvest loses much of the seed.

Is mustard an allergen?

Yes. Some people react strongly, even to small amounts.

Sources

Educational page about a plant. It is not medical advice, not a diagnosis, and not an offer to sell. Traditional use is historical. If you need care, ask a licensed clinician. Questions: hello@meevamed.com.