Nipplewort is an annual or perennial herbaceous plant growing to 1-1.2 m tall, with erect, hairy branching stems and clear (not milky) sap. The leaves are alternate and spirally arranged; the larger leaves at the base of the flowering stem are often pinnate, with a large oval terminal leaflet and one to four small side leaflets, while smaller leaves higher on the stem are simple oval; all leaves have a toothed margin. The flowers are yellow, produced in a capitulum 1-2 cm diameter, the capitula being numerous in loose clusters at the top of the stem. The capitulum is surrounded by a whorl of involucral bracts, the outer ones very small and the inner ones erect, narrow and stiff and all the same length. The eight to fifteen florets are pale yellow and shaped like a tongue with a five-toothed tip. Each has five stamens and a gynoecium composed of two fused carpels. The fruit is a cypsela surrounded by the hardened remains of the involucral bracts.