Summer annual, 0.2-2.5 m tall, found throughout the United States, producing abundant pollen that is a primary cause of hay fever. Leaves hairy on upper surface and margin, densely appressed on lower surface.
Cotyledons are roundish to oblong, purple underneath.
Young leaves opposite, becoming alternate with age, dense pubescence over entire leaf surface. Erect, branched, with long, rough hairs. Male and female flowers are in separate heads on the same plant, the male flowers, usually drooping, are at the top of the plant, while the female flowers are in the upper leaves and bases of leaves. Resembles a crown. Cotyledons with purple underside.