Traditional treatments of Aster were found unsatisfactory in predicting cytological and morphological characteristics of members of various subgenera, sections and subsections of different authors. A realignment of species into these infrageneric categories is presented and is based on sets of shared morphological characteristics of roots or rhizomes, leaves, and phyllaries. Eight subgenera are recognised in Aster . Subgenus Aster is divided into five sections on morphological characteristics: three have X = 9, one has X = 8 and one has X = 7. Subgenus Aster section Dumosi has been redefined and contains all the X = 8 species. Ten X = 5 species and one X = 4 species previously classified in up to six sections of subgenus Aster were found to be morphologically and cytologically related to each other, but unrelated to the other species of Aster . These eleven species have been assigned to the genus Lasallea sensu Semple & Brouillet. Lasallea has been divided in sections and subsections with new combinations presented in this paper.
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Semple et al. (1980) studied this question.