The genus Aster is a huge group of plants. Many, including this one, are tough clump-forming herbaceous perennials originally from the North American prairies, which do well in Sydney gardens. New England asters - Aster novae-angliae - have showy clusters of daisy blooms on stems 50-100cm tall. They begin to flower in summer and may continue into early autumn. There are a number of named cultivars in colours of pinks, cerise, white, mauve and blues. 'Violetta' (pictured) has beautiful deep purple blooms. Asters make good cut flowers for vases.
These plants do best in full sun in reasonable soil with good drainage, and they will stand periods of dryness and heat quite well. The stems can be cut to the ground in winter. They can be propagated by dividing the clumps every few years (discarding the central core); this also keeps the clump more productive. They sometimes suffer from mildew; some cultivars are more resistant to it than others.
Note that the correct botanical name for this plant is now Symphyotrichum novae-angliae.