is an introduced species from Europe, classed as a noxious weed in some parts of the West, and found over a wide area, a large elevation range, and a variety of habitats.
Stems and leaves are may be hairless or sparsely to densely hairy. Stems branch around or above the middle and bear sessile leaves of variable shape. Stem leaves are clasping, with lobed bases, and may be lined with small teeth. Basal leaves are similar in size, generally widest above the middle, and are usually withered at the flowering stage.
The inflorescence is a dense cluster of hundreds of flowers; these are formed of four oblong yellowish-green sepals, four obovate white petals, six stamens and a pistil. Fruits are two-celled, heart-shaped pods, with residual style at the tip, attached by ascending stalks.