Asters (as well as goldenrod) are members of one of the most diverse of all the groups of flowering plants, the Compositae. There are 292 genera of compositae in North America alone and globally this single plant family makes up over 10% of all plant species. One indication of the diversity of the group is evident when you consider that the 19,000+ species in the group comprise shrubs, vines and the occasional tree in addition to the more common herbaceous species.
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 many cases the disk flowers are a different color than the petals so that the entire flower head looks like a single "flower" with a central disk surrounded by differently colored "petals". 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.
There are over 600 species of asters within the family Compositae and we have several types of asters in ZooWoods. However all the species we have so far have yellow disk flowers and white ray or petal flowers. Identifying asters down to their precise species can mean having to tear a flower apart, so we will obviously be content with your ability to identify a particular plant as an aster and let it go at that.
However, asters do come in a wide variety of colors from white to pink, blue and violet. The common purplish flower you see along many Ontario country roads in the fall is another aster, the New England aster. It is a very sun-loving aster (as are many of the aster group), so is unlikely to establish in ZooWoods. Asters as a group are very characteristic of disturbed habitats and in an intact patch of Beech-Maple forest would likely only be found at the edges or in large openings in the canopy.
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