The birthday flower for September is the aster, which represents Love, Faith and Wisdom and symbolizes Valor. Asters are members of the family Asteraceae (sunflowers and daisies belong, as well).
My favorite aster is the Stokes' Aster (Stokesia laevis), a perennial with deep green leaves and intense blue/purple flower heads that float on upright stems. They attract butterflies and have a long cut life. I planted Stokes in a bed that didn't get a lot of attention but it came back faithfully for four years, until my husband did what I should already have done - weeded the bed of all the Bermuda grass that had taken it over. Unfortunately, the Stokes got in the way and out it came. That's OK; it gives me a chance to put it in a better-suited place - and the bed looked so much better when he finished!.