Michaelmas Daisy (Aster novi-belgii) flowers well into autumn and helps keep the bees in business for a while longer. It proliferates readily in sunny spots so there's plenty of it around at this time of year. The patch shown above is in the front garden but drifts of it are often to be seen alongside railway tracks. 

 It came to us from North America in the 18th. century and naturalised. On train journeys I sometimes see a haze of pink and yellow where it grows with Goldenrod (Solidago canadensis), another species from across the pond. Both are of the Asteraceae/Compositae family. 

 We do have an Aster native to the UK. The Sea Aster (Aster trillium) can be found in coastal areas particularly salt marshes and sometimes on cliffstops.