The Compositeae family, sometimes called the Asteraceae family, is enormous, comprising 1,200 genera and at least 20,000 species. Most composites are annual or perennial plants, though the family also contains a few shrubs and trees. Some of the best-loved garden flowers fall into this category, including aster, dahlia, cosmos, coreopsis, gaillardia and Joe Pye-weed.
Composite flowers come in several configurations. The most common garden flower configuration is the daisy-like flowerhead of a composite like cosmos. This flowerhead is radiate, or made up of a central disk, that is actually composed of many tiny flowers surrounded by ray florets (petals). Flowers with ligulate heads feature tubular florets (petals) that arise from the disk instead of merely surrounding it. Composites can also have discoid heads, where the disk itself is the whole flowerhead. Liatris features flower pannicles made up of many disks with chaff, or tiny slender bracts (leaf-like structures), arising from them. Flowerheads can be composed of one single head (like a daisy) or many tightly packed heads (like yarrow).
The leaves can be arrayed opposite each other on the stems or alternate on either side of the stem. They are sometimes basal (at the base of the plant), but are rarely whorled or positioned in groupings around specific points on the stems. The leaves can be simple, compound or deeply dissected, as in chrysanthemums.
Some composites are characterized by milky sap. The common dandelion is one such plant.