It is generally believed that cliffs bear low biodiversity because of their harsh habitats. However, another reason, i.e. insufficient investigation caused by the inaccessibility of the cliffs, could not be excluded. In the genus Aster, two cliff species, Aster fanjingshanicus and Aster tianmenshanensis, respectively growing on slate and limestone cliffs, were previously described. During our extensive field investigations, a third cliff species of Aster growing on granite cliffs from eastern China was found. Based on evidence from molecular phylogeny, morphology and micro-morphology, we propose that it should be treated as a new species and named Aster sanqingensis. It is described and illustrated here. Considering its limited number of individuals, highly localized distribution, and disturbed habitat, we propose to treat it as a Critically Endangered species. Our new finding indicates there is cryptic biodiversity on the cliffs remaining to be discovered.