Composites

Daisies, asters, sunflowers, dandelion, goldenrod, and many other well-loved wildflowers belong to the very large plant family known as the Asteraceae or Composite family. (The old scientific name for this family was Compositae.) In composites, the part of the plant we commonly think of as the "flower" is actually a "bouquet," or composite (thus the name), of several tiny individual flowers. There are two types of flowers that may be included in the "bouquet"- disk flowers and ray flowers. If you think about a daisy, or look at the first illustration on the right, the tiny flowers with five approximately equal length petals in the center are disk flowers, and those around the border with only one long petal are ray flowers. Some composites, such as fringed sage (Artemisia frigida), have flowers that are only composed of disk flowers. Some, such as burnt-orange false-dandelion (Agoseris aurantiaca), have flowers that are only composed of ray flowers. Some such as Patterson tansy aster (Machaeranthera pattersonii), have both.

Composites are usually herbs and shrubs, although there are a few tree composites. Various composites are cultivated for food including sunflower seeds, lettuce, artichokes, chicory, endive, and salsify. The most common human use of this very large family is for garden ornamentals. A few such as chamomile, colt's foot, and wormwood have been used as medicinal plants.

There are more species of composites within the park than any other family of seed plants. Almost 20% of all the types of seed plants in the Rocky Mountain National Park are composites. Composites are found at all elevations and in most habitats in the park, excluding solid rock and ice. Most of these plants are native to the park, but a few, especially Canada, musk, and scotch thistles; spotted and diffuse knapweed; dandelions; and others are among our most invasive exotic weeds.

It should not be a surprise that composites are such an important part of the park's flora, as they are reputed to be one of the largest families of plants with about 1,100 genera and 20,000 species. This family is unusual in that it reaches its greatest diversity in open, temperate areas such as prairie and steppe habitats rather than in tropical forests where many other plant families are most diverse.

Whether you enjoy them for their beauty or their interesting complexity, take some time to look closer at the composites!

Last updated: March 31, 2012

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