(10/17) Why am I writing about flowers when frosty nights and fallen leaves have changed the landscape, anticipating the winter ahead? Granted, the garden is looking quite barren by now, but if you look around, especially along wood edges and fence rows, there are persistent blooms to be seen. Asters and goldenrods, not to mention stubborn dandelions, are still visited by the season’s last hardy pollinators.

These flowers are members of the Aster family, one of the largest families of flowering plants. Plant taxonomists, scientists who name and classify plants, arrange the plant families by similar characteristics. Plants with similar flowers, fruits and seeds are placed in families, even if their leaf and stems structures might not look similar. Members of the Asteraceae (Sunflower family) are all characterized by the presence of several flowers on one flowering structure. Now, consistency in DNA is used to aid taxonomists in defining and grouping plant families, and the more specific genera and species, as well.

As a family of food plants, we eat very few of the Aster family – lettuce, artichokes and sunflower seeds are about all. Many of them are garden favorites – sunflowers, dahlias, zinnias, cosmos, bachelor buttons and many more. Some of our least favorite weeds are included in the family – thistle, ragweed and dandelions. But wait! Dandelions were originally brought to this country as a food plant, and it is a pollinator favorite when there isn’t much else available. When I was studying plant taxonomy, I found this family to be one of the hardest, but also one of the more interesting. The flower anatomy is the reason.

Last summer when I was visiting a friend new to gardening, we were looking over her sunflowers and one flower head was drooping. She remarked that it looked like it died and she needed to remove it. We tipped the flower head up to see the face of the sunflower and saw the radiating swirl of seeds developing on the head. We could see a younger sunflower nearby with the ‘seeds’ in the center smaller and tight; they were the buds that had not yet opened. The ones on the outside were finished blooming and starting to mature into seeds. Between these was a ring with yellow slips (anthers) sticking up. Nearby, there was another sunflower with a bee busily working the part of the flower with the anthers showing and ignoring the rest of the flower head.

You may have guessed that the bee knew the part of the bloom with the yellow anthers was where she would find the nectar and pollen. Sunflowers, and all the other Aster family members, have a grouping of individual flowers on one head called an inflorescence. The flowers bloom, starting from the outside and finish in the center. After flowering, each of those individual flowers becomes a seed. Whether the flower you observe is a sunflower, a zinnia or an aster, they follow the same pattern.

Look at the picture of the cross section of a Tithonia (Mexican sunflower). There are two types of flowers on that flower head. Each of the orange petals has a flower attached at its base; they are the ray flowers. These are the flowers you pull off daisies as you say, "She loves me . . . She loves me not . . . " The flowers in the middle, located on the receptacle, are disc flowers. Some members of the Aster family have only ray flowers; dandelions are an example of this type of inflorescence. Some members of this family have only disc flowers; goldenrod is an example of this type of flower. Besides being a great food source for pollinators, the disc flowers of many larger Asteraceae develop into seeds that birds, especially goldfinches, enjoy.

Each individual disc flower from this Tithonia has all the normal flower parts, but they are small. The petals form a corolla, a collar around the male and female flower structures. The pollen-producing anthers protrude from the flower during its bloom. The pollen-receiving stigma reaches outside the corolla. Nectar is found inside the corolla. When a pollinator visits a sunflower, it brushes up against the anthers as it reaches for the nectar. As it moves around the inflorescence visiting other flowers it brushes pollen onto other stigmas to fertilize those flowers, ensuring that seeds develop.

Why would I expect you might be interested in the anatomy of this group of flowers? Well, the Aster family is an important part of most maintained gardens and natural areas in this region. Many of our gardens include non-native members of the Aster family, annuals that start producing season long color for our landscapes by midsummer. They are usually the last to stop blooming, even after frost has wiped out almost everything else. That makes them important food sources for the migrating monarchs and late working bees. And for me, having them blooming and buzzing with activity while I’m putting the garden to bed for the winter is a sign that I can look forward to seeing pollinators again next year.

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