It is different from all the other asters. It stays short, being two feet at most. It clearly spreads by rhizomes, forming an open stemmed colony. All the other asters have very distinct crowns making them clumping perennials.
I'll have to watch to be sure, but I do not recall the central disc changing colors as the flowers age/get pollinated so much as they just turn brown. The center is a unique yellow color.
I don't know who this aster is and it is the only one that I know of in the wild cultivated gardens. I need an aster expert.