Good information Kent, thanks. This particular aster came as a chunk from Lauribob, and has not reseeded itself that I've noticed (planted as one clump, now larger clump but not really spreading out). I was planning to split it out this fall or spring to increase its presence, even though it has a bit of a stability problem (I'm not big on plant supports). I'm often a bit mystified when others warn of rampant reseeding (rudbeckia, beebalm, now aster) where I see virtually none. Must be a regional/climatic thing. I typically have wet winters with not a lot of freezing, although that trend has certainly changed in the last few years.
In response to Hamilton Square, yes, this aster is more 'frilly' than others I have, although I'm not seeing that so much in Lauribob's photos (from whom I got the initial start). But, she and I live on opposite sides of a mountain range, and often note really different growth habits and/or colors from plants we exchange.
Edited to add: No worries, Hamilton, about straying from subject, it's all relevant to understanding how flowers work.
