Ragweed is an annual herb 20-150 centimeters tall; stems erect, conical-branched in the upper part, angled, and sparsely densely strigose.

The lower leaves are opposite, shortly petiolate, twice pinnatifid, segments narrow, oblong to oblanceolate, entire, with a distinct midrib, dark green above, finely ambiguous or nearly glabrous, gray-green abaxially, densely short hispid; the upper leaves are alternate, sessile, pinnatifid.