Aster (syn. Diplopappus Cass.) is a genus of flowering plants in the family Asteraceae. The genus once contained nearly 600 species in Eurasia and North America, but after morphologic and molecular research on the genus during the 1990s, it was decided that the North American species are better treated in a series of other related genera. After this split there are roughly 180 species within the genus, all but one being confined to Eurasia. The name Aster comes from the Ancient Greek word ἀστήρ (astér), meaning "star", referring to the shape of the flower head. Many species and a variety of hybrids and varieties are popular as garden plants because of their attractive and colourful flowers. Aster species are used as food plants by the larvae of a number of Lepidoptera species—see list of Lepidoptera that feed on Aster. Asters can grow in all hardiness zones.
The genus Aster is now generally restricted to the Old World species, with Aster amellus being the type species of the genus, as well as of the family Asteraceae. The New World species have now been reclassified in the genera Almutaster, Canadanthus, Doellingeria, Eucephalus, Eurybia, Ionactis, Oligoneuron, Oreostemma, Sericocarpus and Symphyotrichum, though all are treated within the tribe Astereae. Regardless of the taxonomic change, all are still widely referred to as "asters" (popularly "Michaelmas daisies" because of their typical blooming period) in the horticultural trades. See the List of Aster synonyms for more information.
Eurybia divaricata (formerly Aster divaricatus), commonly known as the white wood aster, is an herbaceous plant native to eastern North America. It occurs in the eastern United States, primarily in the Appalachian mountains, though it is also present in southeastern Canada, but only in about 25 populations in the provinces of Ontario and Quebec. In the U.S. it is abundant and common, but in Canada it is considered threatened due to its restricted distribution. It can be found in dry open woods as well as along wood-edges and clearings. The species is distinguished by its flower heads that have yellow centers and white rays that are arranged in flat-topped corymbiform arrays, emerging in the late summer through fall. Other distinguishing characteristics include its serpentine stems and sharply serrated narrow heart-shaped leaves. It is very similar to and often confused with E. chlorolepis, E. schreberi and Symphyotrichum cordifolium, though E. schreberi differs in having wider leaves with more teeth, while E. chlorolepis has more rays, longer involucres, and only occurs in the southern U.S. from Virginia to Georgia. The white wood aster is sometimes used in cultivation in both North America and Europe due to it being quite tough and for its showy flowers.