Field mustard is an annual, winter annual, or biennial with erect stems up to 1 m tall. The stems are glabrous or nearly so and commonly glaucous. The basal leaves are petioled with lyrate-pinnatifid blades. The lower cauline leaves are similar to the basal leaves. The upper cauline leaves become oblong to lanceolate, entire to dentate, and are sessile to clasping. The inflorescence is a raceme. The flowers are yellow with four petals. The fruit is a silique 4-7 cm long, terete or nearly so having a beak up to 2 cm long. The siliques are on long pedicels up to 3 cm long. The valves are one-nerved with two delicate lateral nerves. The seeds are minutely roughened, round or slightly compressed laterally, reddish-gray 1-2 mm in diameter.
Roadsides, disturbed areas and waste places, cultivated fields, grain fields, orchards, gardens; to 5000 ft (1500 m); also widely cultivated agriculturally.