White ballmustard

Calepina irregularis, white ball mustard, is a slender annual or biennial herb in the family Brassicaceae and the sole species of the monotypic genus Calepina, native to Mediterranean Europe, northwestern Africa, western Asia east to Iran and Turkmenistan, the Caucasus and southern European Russia. It has spread as a casual or naturalised weed in temperate North America and parts of central Europe. The plant overwinters as a low rosette of glabrous, glaucous, lyrate-pinnatifid basal leaves, then in spring throws up a branching, erect stem 20 to 60 cm tall bearing alternate, sessile, clasping stem leaves with auriculate bases. The branched terminal racemes carry many small, four-petalled white flowers about 2 to 3 mm across. The diagnostic fruit is a small, indehiscent, asymmetrically ovoid one-seeded silicle 2.5 to 3.5 mm long with a short apical beak and a wrinkled, longitudinally veined surface, falling whole at maturity. The species occurs on field margins, fallow ground, vineyards and roadsides on calcareous soils.