Plant classification has been based on flower and fruit structure, but now DNA is being used to help with this, revealing different relationships between plants and causing some name changes. Some plants you have previously know as asters may now be Eurybia, Doellingeria, Symphyotrichum and others. There are many asters still left, providing that reliable pop of autumn colour and structure, in full sun. From observation, when compared to Symphyotrichum, Aster tends to have larger flowers and more roughly textured foliage. They also originate from Europe and Asia.
The iconic daisy flower is actually many flowers grouped together. The centre of the flower contains numerous disc-florets, normally yellow and the part of the flower of more interest to insects and wildlife. The ray-florets, which look like petals, have many colours and sizes and are normally the part which interests the gardener. This flower structure is the same for Doellingeria, Eurybia, Symphyotrichum and others in the invaluable Asteraceae family.