Honey bee (Apis melifera) on Bittercress or Herb Barbara (Barbarea vulgaris)
The genus name Barbarea derives from Saint Barbara, the patron saint of artillerymen and miners, as this plant in the past was used to soothe the wounds caused by explosions. The species Latin name vulgaris means “common”.
This plant grows to about 30–60 centimetres (12–24 in) of height, with a maximum of 1 metre (3 ft 3 in). The stem is ribbed and hairless, branched at the base. It has a basal rosettes of shiny, dark green leaves. The basal leaves are stalked and lyre-pinnatifid, that is with a large terminal lobe and smaller lower lobes. The cauline leaves are smaller, ovate, toothed or lobed. The flowers are borne in spring in dense terminal clusters above the foliage. They are 7–9 millimetres (0.28–0.35 in) long, with four bright yellow petals.The flowering period extends from about April through July. The fruit is a pod of about 15–30 millimetres (0.59–1.2 in).
Chemical substances in this species include saponins, flavonoids, and glucosinolates.
Natural insect resistance and its potential use in agriculture
Most Barbarea vulgaris genotypes are naturally resistant to some insect species that are otherwise specialized on the crucifer family. In the case of diamondback moth (Plutella xylostella) and the flea beetle Phyllotreta nemorum, the resistance is caused by saponins. Glucosinolates such as glucobarbarin and glucobrassicin are used as a cue for egg-laying by female cabbage white butterflies such as Pieris rapae. Indeed, the larvae of this butterfly thrive well on this plant. Diamond back moth females are also stimulated by these chemicals, but the larvae die due to the content of saponins which are apparently not sensed by the moths. This phenomenon has been tested for biological insect control: B. vulgaris plants are placed in a field and attract much of the diamondback moth egg load. As the larvae die shortly after hatching, this kind of insect control has been named "dead-end trap cropping".