Nipplewort is an introduced, annual herb with milky sap. It has leafy stems, simple or sparsely branched, 30-150 cm tall. The leaves are alternate, thin, stalked, oval with toothed to lobed margins. The heads are small (5-8 mm), yellow, and composed of only ray flowers. The involucral bracts are borne in two rows. Numerous heads are borne on slender hairless stalks. Nipplewort is common in fields, roadsides, and in other disturbed areas at low to middle elevations.