Aster chlorolepis Burgess in Small, a member of Aster section Biotia DC. ex Torrey and Gray, has always been considered to be closely related to A. divaricatus, but its taxonomic status has been disputed. To resolve the controversy, over 4000 specimens belonging to the A. chlorolepis-A. divaricatus complex were identified by comparing them to the type specimens of each taxon. Disjoint principal component analysis (DPCA) of morphological data from identified specimens, the first published chromosome counts for A. chlorolepis, and the geographic ranges of both taxa support the segregation of A. chlorolepis from A. divaricatus at species rank. In addition, DPCA allowed identification of 70% of the specimens that could not be identified positively by the above method. Furthermore, the data suggests that A. chlorolepis arose as an autotetraploid derivative of A. divaricatus. Aster chlorolepis may represent, therefore, the long-missing ploidy link between the diploid species and the hexaploid and octoploid species in Aster section Biotia. A range map of and a taxonomic key to A. chlorolepis and A. divaricatus are presented.