- Name also: White Charlock, Runch, Jointed Charlock
- Family: Mustard Family – Brassicaceae (Cruciferae)
- Growing form: Annual herb. Root thin.
- Height: 30–60 cm (12–25 in.). Stem base stiffly haired. Radish-like smell when crushed.
- Flower: Corolla regular (actinomorphic), pale yellow–lemon (occasionally white), approx. 1.5–2.0 cm (0.6–0.8 in.) wide; petals four, 15–20 mm (0.6–0.8 in.) long, clearly veined. Sepals 4, erect, long-lasting. Stamens 6, of which 4 long and 2 short. Gynoecium fused, a single carpel. Inflorescence a raceme, extending in fruiting stage.
- Leaves: Alternate, stalked. Basal leaf-blades pinnately lobed, terminal lobe larger than others. Stem leaves narrow, large-toothed.
- Fruit: Many-seeded, indehiscent, jointed, siliqua, constricted between seeds (tapering), breaking into one-seeded portions when ripe, 4–8 cm (1.6–3.2 in.) long with deep constrictions between seeds, tipped with 10–25 mm (0.4–1 in.) long bristle. Stalk approx. 15 mm (0.6 in.).
- Habitat: Cereal fields, especially spring cereal fields, potato fields, fallow land, heaps of earth, waste ground, roadsides, lawns.
- Flowering time: July–August.
Wild radish arrived in Finland with people, probably from somewhere around the Mediterranean. It became common in the 19th and 20th centuries, and nowadays it is quite a common weed in the southern half of Finland. The seeds, which ripen inside siliquae that are deeply constricted between each seed, have adapted very well to the life of a weed. When it is mature the siliqua breaks into pieces which are just the right size to find their way into uncleaned grain seed, although nowadays efficient cleaning has curtailed its spread. Wild radish that is sown with spring grain usually only germinates best the year after it has been sown. The siliqua’s thick well prevents the seed from sprouting and some of them usually spend a long time as part of the seed bank in the soil. The seed is so well protected inside the siliqua that it can safely wait there for even decades or travel unharmed through ruminants’ digestive tracts.
The best place for wild radish to complete its life cycle is the cereal field, although it is happy in among potatoes and other vegetables too. On grassed roadsides they can run rampant for the first couple of years, until the perennial species begin to assert themselves. On cut lawns the species has an even shorter lifespan because it will not even get to produce seeds. Wild radish prefers acidic land, which explains why it is rare in the Åland Islands, where its place is taken by another member of the Mustard family, wild mustard (Sinapis arvensis). They look quite similar but the latter’s sepals are spreading and its leaves are not so lobed. In the fruiting stage wild radish can easily be told apart from other Finnish members of the Mustard family due to its siliquae.
Wild radish’s very close relative garden radish, which has two cultivated varieties, also grows in Finland as a rare casual alien or as an escape from cultivation. Its corolla is pink, purple or white, and its siliqua is oval, only slightly jointed or without any joints at all. Cultivated plants do not usually get to flower so that the plant can concentrate on developing what lies under the ground. If the plants are not harvested and allowed to flower they are very attractive to butterflies.