aster, used informally to describe any of various chiefly fall-blooming (often with showy flowers) leafy-stemmed herbaceous plants (Aster and related genera) in the Asteraceae family. True asters, those of the Aster genus, are almost exclusively Eurasian, the alpine aster (A. alpinus) being the only North American species of the 180 in the genus. Despite physical similarities, molecular data has led to a taxonomic overhaul of the genus, with the majority of the North American species reassigned to the genera Doellingeria, Eurybia, Ionactis, Oclemena, and Symphyotrichum. Indeed, many species are now understood to be more closely related to Solidago than Aster, and thus the revision more accurately reflects evolutionary lineages.

Many perennial wildflowers and garden varieties are known as asters. Hairy golden aster (Heterotheca villosa), New England aster (Symphyotrichum novae-angliae), Schreber’s aster (Eurybia schreberi), and mountain aster (or whorled wood aster; Oclemena acuminata) are all common wildflowers in North America, and some are used as ornamentals. The Tatarian aster (Aster tataricus) is a true aster native to Siberia and a popular garden variety.