Thickhead is an erect or straggling annual herb (living 1 season only). Leaves are alternately arranged along the stem. Leaf shape is variable, smaller upper leaves are generally elliptical, larger lower leaves have two lobes at the base. All leaves have toothed margins. Flower heads droop while forming and are orange-pink. Base of plant, lower stems, some veins and some leaves have a purple colouration. Seed has hairs (pappus) which are white and tinged reddish or mauve. Stem is round in cross-section and exudes watery liquid when cut.