Fruit a narrow siliqua, 15—30 × 1—4 mm, walls (valves) with a distinct mid vein, style 2—3.5 mm, with one row of seeds in each room. Some plants have curved, slender fruits 1—2 mm broad (var. arcuata), others have straight, stouter fruits 2—3 mm broad (var. vulgaris), see Comments.
This species can only be mistaken for one of the other introduced, yellow-flowered crucifers, Sinapis arvensis or possibly Raphanus raphanistrum, but both these are very rare and ephemeral and any confusion is unlikely. They are both annual, without basal rosette, whereas Barbarea vulgaris always has one or more basal rosettes, withered on flowering shoots.
Introduced. Barbarea vulgaris has been found in one Norwegian settlement (Longyearbyen in 1960) and in three Russian settlements: in Colesbukta in 1935 and 1936 but with suggestions on herbarium labels that it has had a more extended stay (however, now disappeared as has the settlement), in Pyramiden in several years from 1961 to 2014, thus also long after the mining was discontinued and the settlement abandoned in 1998, and in Barentsburg where it has been found in fair amounts on every visit from 1988 to 2011. The species has established long-lasting populations in both these settlements, in Pyramiden for more than 50 years, in Barentsburg for more than 25 years, which are long time spans for a mainly biennial plant with intermittent reproduction. It strongly suggests the existence of a seed bank. The soil in central parts of the Pyramiden settlement is reported to have been imported (S. Coulson pers. comm.) and the plant may have followed with the soil. In Barentsburg it probably has followed with animal fodder.
The general range is European and W Asian.
Barbarea vulgaris is one of only two aliens that have established long-lasting and regularly reproducing populations in Svalbard (the other one is Anthriscus sylvestris). Why has it been so successful in the Russian settlements, but only with a single appearance in a Norwegian settlement? The more extensive and long-lasting husbandry and import of animal fodder in the Russian settlements may be the main explanation. The plants observed in Barentsburg in 1988 and in several later years is var. vulgaris, which is assumed to be the least hardy of the two varieties (in Scandinavia var. arcuata reaches both farther north and higher up in the mountains than var. vulgaris). The taxonomic value of the two varieties is, however, uncertain. With increased summer temperatures and prolonged growth season due to climatic change, the outlook for this species in Svalbard is good (Alsos et al. in press). However, a spread away from the settlements is unlikely in the foreseeable future.