The genus Boltonia mainly occurs in eastern North America. It comprises five species that grow in moist to wet habitats. The genus was previously suggested to be closely related to the Old World Kalimeris. However, morphological data by Gu and Hoch provided evidence that these two genera were not closely allied. DNA sequence data by Noyes and Rieseberg supported Boltonia's close affiliation with New World Symphyotrichum, Batopilasia byei (as Erigeron byei), and genera of Machaerantherinae. In our phylogeny based on ETS and ITS sequence data with Aster amellus as the outgroup Kalimeris appears basal, while Boltonia is the most derived lineage. Batopilasia and Chloracantha are sisters and this clade in turn is sister to Boltonia, thus supporting Nesom's most recent suggestion of relationship; Symphyotrichum in turn is sister to this clade. Furthermore, our sequence data resolves three lineages within Boltonia that conflict with current taxonomic hypotheses. B. asteroides var. latisquama, and B. asteroides var. recognita are separated from B. asteroides var. asteroides and are placed in a separate clade together with B. decurrens and B. apalachicolensis.

Key words: Astereae, Boltonia, external transcribed spacer region (ETS), internal transcribed spacer region (ITS), molecular data