Tansy Mustard is a native annual with stems from 4-32 inches tall. The variable, alternate leaves are largest at the base. Leaves are once or twice pinnately divided into quite narrow fern-like lobes (D,E).  At the tips of the branches are elongating clusters of yellow flowers each with 4 tiny petals about 1/8 inch long (C). Fruits are narrow, club-shaped pod-like siliques up to 1/2 inch long borne on slightly ascending stalks of the same length or slightly shorter than the siliques (B,C).

Very similar Flixweed (Descurainia sophia) also has fern-like leaves and tiny yellow flowers, but the siliques are narrower (about the same diameter and not club shaped) and longer than the stalk.