What happened to the Asters?  Why are they now in Symphyotrichum and Eurybia?

Since Linnaeus founded the genus Aster, it has always been a difficult genus, for experts as well as layfolk.  Ordinary people have had great trouble telling the species apart, since species identification has depended on many variable characters.  Experts, on the other hand, have had trouble keeping them together.  There is so much variation in the genus that people have long agreed that it needed to be split apart, and some have tried; however, no one came up with a scheme based on the visible characters that everyone was satisfied with.  In recent years, botanists have turned the tools of molecular classification on the genus, examining the sequences of the DNA that codes for the characters of each species.  These results have shown that the genus really does contain many species not closely related, and, consequently the genus has been divided up.  In particular, native North American asters are not related, for the most part, to native Eurasian asters.  Unfortunately for those who don't like changing names, the plant that Linnaeus first used to describe the genus Aster was Eurasian, and thus, by the laws of botanical nomenclature, the Eurasian species got to keep the name.  There is now only one native Aster in North America and it is a western species.  Most, but not all, asters in Virginia have gone into the genus Symphyotrichum.  Botanists, however, have no jurisdiction over the common names that everyday folk call them, so the species will all retain the common name aster until everyday people start calling them something else.