Narrow-leaf bittercress

Cardamine impatiens, the narrow-leaved bittercress, is a slender hairless biennial in the family Brassicaceae. In its first year it forms a low rosette of sterile, dark-green pinnate leaves; in the second year it produces one to several upright, leafy flowering stems typically 30–60 cm tall. The stem leaves are pinnately compound with several pairs of lanceolate, sharply dentate leaflets and a slightly longer terminal leaflet, the leaf bases distinctively clasping the stem with rounded auricles. From May to July it produces loose terminal racemes of tiny white flowers with four narrow petals only slightly longer than the calyx, sometimes much reduced or even absent. The fruits are slender erect siliques in which the seeds are arranged in a single row along each side of the central membrane; at maturity the pod walls coil away explosively to project the seeds, an adaptation reflected in the epithet impatiens. It is native to temperate Eurasia from Ireland and Spain east to the Russian Far East, growing on damp shady walls, woodland banks and disturbed shaded ground.