- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual herb.
- Height: 40–80 cm (16–32 in.). Stem base–halfway branched, quite erect branched, bluish, lower part hairy, upper part glabrous.
- Flower: Corolla regular (actinomorphic), yellow, approx. 1 cm (0.4 in.) across; petals 4, dark-veined, 7–9 mm (0.28–0.36 in.), long. Sepals 4. Stamens 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence an elongating raceme in fruiting stage.
- Leaves: Alternate, stalked. Basal leaves’ blade pinnately lobed, terminal lobe large, elliptic. Stem leaves’ blade elliptic–lanceolate, with toothed–entire margin, glabrous, bluish green.
- Fruit: Many-seeded, opens lengthwise, 4-edged, 1–2 cm (0.4–0.8 in.) long siliqua, parallel to stem, terminated by a 2–3 mm (0.08–0.12 in.) long, seedless beak. Stalk 2–5 mm (0.08–0.2 in.).
- Habitat: Rubbish tips, harbours, loading areas, mustard processing plants, wasteland, sometimes gardens.
- Flowering time: June–September.
Mustard family plants bear a great resemblance to each other and they often also mutate. Black mustard is believed to be native to the eastern Mediterranean or the surrounding area, but nowadays it grows virtually all over Europe. It grows casually in Finnish harbours and other loading areas, but finding the plant takes a little bit of effort and luck. It has been cultivated for millennia as a spice. Initially leaves that had been pickled in vinegar were used culinarily: it wasn’t until the 13th century that plant seeds were pounded and blended into mustard. Mustard owes its aroma to mustard oil, which is secreted into the plant’s specialized storage cells, idioplasts. Black mustard is one of the mustard industry’s main ingredients and is used to make very strong mustard. Judging by the amount that is produced, mustard is the world’s most important spice.
Mustard is also prepared from Cabbage family member brown mustard seeds. Last year cultivation of the species became more widespread in Finland, and it can now be found more readily outside fields too on e.g. waste ground and around dumps. The best way to tell it apart from black mustard is in the fruiting stage: the species’ siliquae are spreading, clearly larger and cylindrical (terete = round in cross-section).