Asters are actually very complicated flowers.
What looks like the flower is really a collection of very tiny tubular flowers, grouped together in a central disk, and surrounded by so-called ray flowers or petals. You may be familiar with other members of the composite flower family, for example dandelions or sunflowers , where the organization of a central disk of flowers surrounded by a ring of ray flowers is more obvious. In addition, though each flower head is already composed of numerous flowers, many composites have multiple flower heads such that the number of actual flowers on any particular plant can number in the thousands. Evolutionary biologists have speculated that the presence of so many flowers in such close proximity facilitates numerous new genetic combinations through cross-pollination. A high degree of genetic variability might allow composites to exploit a wide variety of habitats and make them particularly adaptable to changing environmental conditions.