This adventive perennial wildflower is 1-3' tall, branching occasionally. The stems are medium green and minutely rough-pubescent to glabrous. The spreading alternate leaves are up to 6" long and 2" across; they are odd-pinnate or double odd-pinnate with 5-11 lobes, medium green, and minutely rough-pubescent to glabrous. The slender lobes are linear-oblong and sometimes have 1-2 dentate teeth or smaller cleft lobes; they are 1/3" across or less. Irregularities in the structure of the leaves are rather common. The petioles are up to 2" long. Occasionally, the upper stems terminate in individual flowerheads on long naked stalks (peduncles). These stalks are 2-12" long and finely grooved. The flowerheads are about 1½3" long and a little less across. Each flowerhead consists of a cylindrical head of numerous disk florets, which is surrounded by 4-11 drooping rays (ray florets). A mature head of disk florets is ¾1¾" long; it is initially gray or greenish gray, later becoming dark brown. The rays are about ½1¼" long, oblong in shape, and slightly notched at their tips; they are either yellow, maroon (reddish brown), or yellow with basal patches of maroon. The typical form of Mexican Hat has yellow rays, while plants with maroon rays are referred to as f. pulcherrima. The bottom of each flowerhead is defined by 2 series of small narrow bracts; these are largely hidden by the drooping rays. The blooming period occurs during the summer and lasts about 1-2 months. Fertile disk florets are replaced by small oblongoid achenes; each achene usually has one or more tiny scales at its apex. This plant spreads to new areas by reseeding itself.