Here's a rush aster flower head at the moment of its fullest development. All the center flowers are open. In that center, the outer ones open first. As the center flowers age, they turn from yellow to purple, typical of most asters. This species has relatively long ray flowers, but still only up to 15 mm. Rush aster mostly appears in fens and bogs in AK, CO, CT, IA(T), ID, IL, IN(R), MA, ME, MI, MN, MT, ND, NE, NH, NJ(E), NY(T), OH, PA(E), RI, SD, VT, WA(T), WI, WV, WY, and in all of Canada except LB. Washtenaw Co MI, 9/9/11.