Autumn sneezeweed is a late-blooming perennial with branching, winged stems. Flowerheads are many, all yellow, with 10–18 ray florets fan-shaped, notched, reflexed downward. The large disk is dome-shaped. Blooms August–November. Leaves are basal or mostly on the lower parts of the stem, with only smaller leaves on the upper stems; alternate, narrowly lance-shaped, with or without a few teeth; the leaf tissue extending down the stem as wings.
Similar species: Four heleniums grow in Missouri. Bitterweed and purple-headed sneezeweed have their own entries in this guide. The fourth, Virginia sneezeweed (H. virginicum) is the most like autumn sneezeweed. A state endangered and federally threatened species, it only occurs in about 9 of our southern Ozark counties, primarily in boggy, sinkhole pond habitats. Oddly, the only other populations in the world are in the state of Virginia, and nowhere else. It is found in moister soils than autumn sneezeweed, and its leaves are well-developed along the leaf stem; basal and lower leaves are absent at flowering; it blooms July–September.