New England American-aster (Symphyotrichum novae-angliae*) is a native and widely planted perennial who flowers from late summer into fall. The plant's narrow leaves have entire margins and clasp the conspicuously hairy stems. Each roughly 1.5" wide flower head is comprised of tiny yellow disc flowers and at least 40, typically purple ray flowers. The flowers of New England American-aster offer nectar to a variety of late season insects, including American Coppers, Pearl Crescents, and migrating Monarchs. Pearl Crescent caterpillars also feed on this species. (To view the following images in full-size, click here.)
*Many sources refer to this plant as Aster novae-angliae (commonly New England Aster), but more recent taxonomies, like Flora Novae Angliae by Arthur Haines (free online version at GoBotany), place this plant in a different genus. Tricky, tricky.