Pecos sunflower is an erect annual with mostly hairless stems, which reach from 1-3 m in height. Leaves lower on the stem are opposite one another, whereas higher up, the leaves become alternate. Leaves are narrowly teardrop shaped, are usually 7-15 cm long, and have smooth leaf edges (the lower leaves may have a few small teeth). Three conspicuous, roughly parallel veins run outward from the base of the leaf toward the tip. Flower heads occur 3-5 per branch and are 5-7 cm in diameter. Two to three overlapping rows of green, narrowly teardrop shaped, leaf-like structures (each 2-4.5 mm wide) closely cup the outside base of the flower head. Flower heads have a reddish-purple center, composed of about 50 tiny flowers (disc florets), surrounded by 12-20 yellow petals (each petal is the largest part of an otherwise tiny flower called a ray floret). The seeds are small (3-4 mm long) and lack hairs but have 2 small scales at their base