Flower: The flowers are yellow with four petals.
Seed: The seeds are minutely roughened, round or slightly compressed laterally, reddish-gray 1-2 mm in diameter.
Stem: Field mustard has stems up to 1 m tall. They are glabrous or nearly so and commonly glaucous.
Leaf: 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.
Leaves are petioled, +/- pinnatifid or lobed, 1-2 dm long; upper leaves, sessile, auriculate-clasping, lance-oblong, subentire, glabrous; pedicels spreading, 1-2 cm. long; sepals narrow-oblong,yellowish, 4-5 mm long; petals yellow, spatulate, 6-8 mm long; siliques not torulose, terete, 2-5 cm long, stout with a stout beak an additional 1-1.5 cm long.