Asteraceae: Wildflowers of the Aster/Sunflower Family (Composite/Compositae). Pictures and help with wildflower Identification from Thomas J. Elpel, author of Botany in a Day. The easy way to identify flowers.
Thomas J. Elpel
PO Box 697
Pony, MT 59747

Aster or Sunflower Family
(also known as the Composite Family: Compositae)

Key Words: Composite Flowers in disk-like heads

The uniqueness of the Aster or Sunflower family is that what first seems to be a single large flower is actually a composite of many smaller flowers. Look closely at a sunflower in bloom, and you can see that there are hundreds of little flowers growing on a disk, each producing just one seed. Each "disk flower" has 5 tiny petals fused together, plus 5 stamens fused around a pistil with antennae-like stigmas. Look closely at the big "petals" that ring the outside of the flower head, and you will see that each petal is also a flower, called a "ray flower", with it's petals fused together and hanging to one side. Plants of the Aster family will have either disk flowers or ray flowers, or both. When the seeds are ripe and fall away, you are left with a pitted disk that looks strikingly like a little garden plot where all the tiny flowers were planted.

The green things outside the flower head that might look like sepals are actually "bracts" (modified leaves) surrounding the disk. The true sepals have been reduced to small scales, or often transformed into a hairy "pappus", or sometimes eliminated altogether.

One of the best clues for identifying members of this family is to look for the presence of multiple layers of bracts beneath the flowers. In an artichoke, for instance, those are the scale-like pieces we pull off and eat. Most members of this family do not have quite that many bracts, but there are frequently two or more rows. This is not a foolproof test, only a common pattern of the Aster family. Next, look inside the flower head for the presence of the little disk and ray flowers. Even the common yarrow, with its tiny flower heads, usually has a dozen or more nearly microscopic flowers inside each head, and the inside of a sagebrush flower head is even smaller. Keep in mind that many members of this family have no obvious outer ring of petals, including sagebrush.

The Asters are the largest family of flowering plants in the northern latitudes, with 920 genera and 19,000 species found worldwide, including 346 genera and 2,687 species in the U.S. and Canada. Only the Orchid family is larger, but it is mostly restricted to the tropics.

Many species of the Aster family are cultivated as ornamentals, including Marigold, Chrysanthemum, Calendula, and Zinnia. Surprisingly few are cultivated as food plants other than lettuce, artichoke, endive, plus the seeds and oil of the sunflower.

The Aster family consists of two subfamilies. The Dandelion subfamily includes a variety of plants with dandelion-like flowers. The ray flowers typically over-lap all the way to the center. The petals have strap-like, parallel edges with squared-off ends. The stems and leaves of all species have milky juice, and all are edible, but bitter. Bitter substances like dandelion greens are helpful as an appetizer to stimulate digestive secretions before the main meal. Eating your dandelions can help reduce problems with indigestion later. Keep in mind that there are many other plants with milky juice that are not related to Dandelions, including some that are poisonous. Be sure to check the blossoms for proof.

The Aster subfamily is much larger, made up of eleven tribes, some of them radically different from the others. Thistles and knapweed are found in the Artichoke tribe.

The Chamomile tribe includes the most aromatic members of the Aster family, such as sagebrush, yarrow, tansy, and of course, chamomile. As a kid I encountered many different species of sage (Artemisia). There are 19 species just in Montana. But without a patterns approach to go by, I didn't have a clue where to start, so I brought each specimen to the university herbarium for identification. These days, when I see a new fuzzy green-gray plant, I immediately crush a leaf and smell it to test for a sage-type smell. Each species smells different, but there is a common pattern to the smell that is undeniably sage-like.

I also test for members of the Sunflower tribe by smell. Most species are resinous, much like pines, useful medicinally for their expectorant properties. Crush up the head of a sunflower and smell it to get a sense of the resin odor. Once you learn the patterns of smell from the various families, subfamilies and tribes, you will be able to accurately identify many new plants with just your nose.

© 1997 - 2011 Thomas J. Elpel
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