Biennial or short-lived perennial.
Solitary herb with a tap root, producing a rosette the first year, a reproductive stem the next year, but also often producing lateral rosette(s) at the base of the stem after flowering, thereby becoming perennial. Flowering stems 30—50(60) cm, erect, with several leaves, stems often branched in the inflorescence. Stems and leaves glabrous or with sparse hairs on leaves and stems; hairs white and flattened.
Leaves alternate. Rosette leaves with petiole 2—7 cm and blade 8—10(15) × 2—5 cm, pinnately divided to or nearly to the mid axis (pinnatifid or pinnatisect), with a large, rounded terminal lobe 2.5—5 × 1.5—5 cm and 1—4 pairs of much smaller and narrower lateral lobes. Lobes sparsely, shallowly and irregularly dentate. Stem leaves much smaller than rosette leaves, the lower ones similar to rosette leaves but with shorter petioles having a clasping base with auricles, the upper ones undivided but with sharp teeth or lobes, nearly sessile or sessile and strongly clasping.
Inflorescence an ebracteate raceme, very short at the beginning of flowering, ca. 1.5—2 × 2—2.5 cm, elongating appreciably during flowering to 10—12 cm or more, with secondary branches from upper leaf axils.
Flowers on spreading pedicels 4—8(9) mm, radially symmetric with 4 free sepals and petals. Sepals ca. 4 × 1.5 mm, pale green with a narrow, white hyaline margin, appressed during the flowering, the two lowest sepals saccate at base. Petals ca. 8 × 3 mm, with long claw and obovate limb, yellow with darker veins. Stamens 6; filaments ca. 5 mm; anthers narrow, 1—1.3 mm. Gynoecium of 2 carpels with 2 rooms separated by a secondary, hyaline wall.
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.
Sexual reproduction by seeds; no vegetative reproduction. Pollinated by insects. Seed-set is probably regular enough to upkeep a few populations (see Distribution). Fruits with mature seeds have been observed a few times.
There is no special adaptation to seed dispersal.
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.
Disturbed ground within settlements, usually coarse-grained and dry.
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.
Alsos I.G., Ware, C. & Elven, R. In press 2015. Past arctic aliens passed away, current ones may stay. – Biological Invasions.