GROWTH HABIT: An annual or winter annual, 1 to 3 feet tall.
LEAVES: Leaves are 2 to 8 inches long, 1 to 4 inches wide, lower ones deeply lobed, upper leaves are merely toothed and may appear short-stalked or stalkless (but not clasping).
STEMS: Stems are erect, with stiff hairs, at least on lower portions.
FLOWER: Flowers are yellow with 4 petals.
SEEDS: Seed pods (siliques) lack hairs, are 1-1/4 to 2 inches long, oval to round in cross sections, and supported on short (1/10 to 3/10 inch) pedicels. See pods have a constricted beak above the uppermost seed. The beak of wild mustard is 3/10 to 6/10 inch long, obviously flattened (2-edged or 4-angled), and valves (pod halves) each have 3 to 5 prominent lengthwise veins. Pods are somewhat spreading. White mustard (B. Hirta Moench) resembles wild mustard, except that pods and pedicels of white mustard are covered with coarse spreading hairs.
OTHER: Wild mustard, also called charlock mustard or kaber mustard, has been classified as B. arvensis (L.) Rabenh, Sinapsis arvensis L., and S. kaber DC. By various authors. It is adventive from Europe; now widespread, infesting roadsides, cultivated fields, ditchbanks, and waste areas.