Garlic mustard is a biennial forb growing from a taproot. Rosette leaves are rounded, scallop-edged, and dark green to purplish-green. Stems can grow up to 4 ft (1.2 m) tall, usually with a single unbranched stem. Leaves are alternate, coarsely toothed, and become smaller and more triangular further up the stem. White flowers are produced in small clusters at stem tips, each with four white petals and six stamens. Fruits are thin capsules that are held erect on short stalks. Each capsule contains two rows of black, cylindrical seeds.