In the genus Aster we find many variable species which intergrade with one another; even botanical specialists would be cautious about stating the number of species in the two parks. A conservative estimate would be between 12 and 18. The ray flower color varies from violet to pink or almost white. Flowering extends from late July through mid-September, and the plant occupies dry, open places. {Plants of Yellowstone and Grand Teton National Parks by Richard J. Shaw pg 140}