Much-branched annual. Flowerheads few to many on naked stems above the foliage, yellow, the 5–10 ray florets reflexed and notched; the disk bowl-shaped, pointing skyward, yellow. Blooms June–October. Leaves profuse, linear (very narrow), to 1½ inches long with smaller leaves arising from axils of larger ones. Plant contains bitter, toxic substances, and cattle forced to graze on it in overgrazed pastures produce bitter milk, thus the name bitterweed.
Similar species: Four species of Helenium grow in Missouri. The others are discussed elsewhere in this guide. All have rounded disks and yellow, fan-shaped, drooping ray flowers. This is the only one that is annual, has profuse, linear leaves, and lacks wings of leafy tissue on the stems.