The Composites have floral parts consisting of multiple tiny flowers--complete with minuscule pistil, stamens, petals, and sepals--merged into one head or disk.
One blossom may have dozens or even hundreds of these little flowers. Inspection of a daisy, for instance, will reveal an outer ring of tiny yellow flowers already open, while the central part of the disk contains flowers that are still closed up, unless the bloom period is near its end. Surrounding the disk are the long while “petals” or rays, each a single infertile flower lacking pistils and stamen.
This configuration of a central disk surrounded by rays is common among the composites, which include Echinacea, black-eyed Susan, daisy, calendula, sunflower, coltsfoot, as well as flowers without rays, such as liatris and pearly everlasting. Most Composites also have two or more layers of bracts, leaflike structures overlapping on the underside of the flower.
Many Composite family members are aromatic. Crush and sniff a leaf of goldenrod, and you’ll get a smell similar to that of aster and Canadian fleabane; all three are members of the Aster subgroup, with irritating compounds that give the plants diuretic (stimulating urination) and decongestant (clearing the sinuses) properties.
Plants in the Camomile subgroup are also aromatic but with more widely differing scents. It includes many medicinals: yarrow, tansy, pineapple weed (similar to camomile but smelling like pineapple), and the Artemisias—mugwort, wormwood, tarragon, and a number of cultivated ornamentals, all with feathery leaves.
The Dandelion subfamily features “strap-shaped” petals, that is, rays with mostly parallel, rather than tapered edges, and no disk flowers. Most of them contain a bitter, milky juice. Many are nevertheless edible, with the bitterness contributing to their functions as liver cleansers and digestive tonics. These include chicory, goat’s beard, and wild lettuce.
Another subfamily contains thistles, artichoke, and burdock, all of which have edible parts—the roots of burdock, the artichoke flower buds sold in markets, and the peeled stalks of young thistles. They are all nourishing to the liver, as are milk thistle seeds. Their prickly parts make them easy to identify, although sometimes difficult to harvest.
Boneset and gravel root (Joe Pye weed), both flowering in damp places in late summer, belong to another sub-group. Lacking ray flowers, the scruffy little clusters of flower heads look quite similar except in color—boneset, a fever herb, is white, and gravel root, used to treat kidney stones, is pink.
Ragweed, surprisingly, is also a Composite, although the flowers are so tiny you can hardly see them. They are hidden under green, bell-shaped structures rising from the bases of the leaf stems and are rarely noticed, but their formation, seen under magnification, reveals the structure of a Composite flower.
