Abstract: Collections of Aster ageratoides var. gerlachii (Hance) Chang from Shennongjia, Hubei Province, central China, have long been erroneously referred to A. ageratoides var. micranthus Ling. A comparative study on the morphology and cytology of the two varieties was conducted to gain a better understanding of their relationships. The possible factors causing the misidentification are discussed and the diagnostic characters between the two varieties are redefined. The absence of horizontal rhizome in var. micranthus was found to be of important taxonomic value. A. ageratoides var. micranthus was a diploid with the karyotype formula of 2n=2x=18=18m, with the karyotype belonging to 1A type in karyotypic asymmetry, whereas A. ageratoides var. gerlachii was a tetraploid with the karyotype formula of 2n=4x=36=32m+4sm (2SAT), with the karyotype belonging to 2A type. A. ageratoides var. gerlachii is a newly recorded taxon in Hubei.

Key words: 狭叶三脉紫菀, 小花三脉紫菀, 神农架