Aster cordifolia 'Blue Heaven'

Tall stems end in open sprays of smallish lilac-blue flowers. This flowers for ages on much branched, dark stems with small, slim mid-green leaves. There seems to be a muddle as to what exactly this is, is an ericoides or a cordifolia type. Also it is now listed under Symphyotrichum - just to make it more confusing! Whatever it is, its nice.