This is a world-famous plant, and a great perennial for American gardens from Zone 6 south.. It is not a North American aster like many of the others. And unlike the American native asters, it doesn't wait until fall to bloom. Aster frikartii or Frikart's Aster blooms from early summer to fall, adding great color for a long period. Wonderful lavender/blue flowers are about 2 1/2 inches across and cover the plant.
This is the aster you see at garden centers every year grown much like a chrysanthemum--nice neat rounded plant about a foot tall in full bloom. However, once you put it in the ground, it forms a bushy plant about 2-3 ft. tall, and gives you months of color and cut flowers. It is a spectacular bloomer in gardens all over the south and along the northern Pacific coast.
The story of this plant is interesting. It is a cross between two aster species A. amellus from eastern Europe and A. thomsonii from the Himalayas. The cross was made by Karl Frikart in Switzerland around 1920. Ever since, various versions of this fantastic success have been created and named. The cultivar Monch is the most famous, but another similar one, Wonder of Staffa is also well-known. A more recent one is called Floras Delight. They're all Frickart's aster, and they're all beautiful.