11. Aster L. (aster)

About 180 species, North America (1 native taxon), Europe, Asia, introduced widely.

As has been the case with most of the big genera of Asteraceae, recent studies have caused taxonomists to reevaluate the generic limits and taxonomic interrelationships among species groups. A number of earlier studies of individual species groups had already caused the reclassification of some taxa to other portions of the tribe. For example, the aberrant A. ptarmicoides (Nees) Torr. & A. Gray is now generally accepted to belong to a small group of species most closely related to Solidago (Brouillet and Semple, 1981). The first comprehensive study of higher-order relationships within the Aster group was by Nesom (1994), who concluded, based upon morphological comparisons as well as on biogeographical and cytological data, that the New World and Old World species were not very closely related within the family. His work resulted in a new framework that recognized 7 major lineages of former asters and more than 25 total genera. Since that time, additional morphological studies (Nesom 2000) as well as ongoing research involving molecular data (Noyes and Rieseberg, 1999; Semple et al., 2002) have supported this general classification while fine-tuning the numbers and limits of the various smaller genera. Although Aster remains the largest genus in the group, the only species native to North America is the circumboreal A. alpinus L. The sole true aster found growing wild in Missouri is an escape from gardens.