New England Aster
The tallest of our many native asters, branching toward top of stems. Flowerheads many, about the size of a quarter, with many (more than 40) ray florets, reddish purple to purple (pink to white elsewhere, and crimson, magenta, and darker shades in cultivation). The disk is yellow. Blooms August-October. Leaves alternate, many, narrowly lance-shaped, clasping the stem, and auriculate (with ears).
Similar species: There are 24 species of Symphyotrichum in Missouri, plus many hybrids and varieties. This species is notable for its large flowers, with many petallike ray florets, and its many stem leaves.