This biennial plant begins as a rosette of large leaves, and then progresses into a branching, erect plant with burs during its second year. It can flower as soon as June, and last through October in some cases.
Cotyledons are egg-shaped and widest near the apex (obovate) with a waxy surface. Young leaves are also egg-shaped, except at the truncated base. Plants produce a rosette of large leaves in the first year. For the second year, it develops a branched stem which has leaves arranged in an alternate fashion. Stems are erect, branched, hollow, hairy, and ridged. Stems may reach 5 ft in height.
Large basal rosette of leaves with hollow lower petioles, and flowers with hooked bracts. After senescence, the remaining burs on the stems of common burdock may resemble a thistle. However, the dried flowers of thistle plants do not have hooked bracts that stick to clothing like common burdock.
Flower Seed Head:
Flowers occur in clusters at the ends of branches (terminal racemes) or in clusters that arise from the region between the stem and leaves (axillary racemes). The flowers are purple to lavender, occasionally white, with outer bracts that are "hooked." Flowers dry to a bur, and the hooked bracts are often confused with a thistle.
The seeds develop in an achene, mottled dark-gray to black, 4-7 mm long, with a pappus of short bristles. The hooks on the achenes will often catch on clothing and animal fur to aid in seed dispersal. The individual seeds are brown to dark gray, rough, and usually 4 to 5 mm in length.
Being biennial, this plant prefers undisturbed soils such as along fence rows, open farmland, waste places, roadsides, and undisturbed woods. Common Burdock can be found across the upper half of the United States.