Herbs, shrubs and even trees are in the Sunflower Family with flowers that fool the beginner. What seems to be a single flower is actually a cluster of many flowers of two kinds. The strap-shaped forms on the outer edge that look like petals and are each a complete flower with all of the parts that a flower needs. They are called ray florets. The tightly packed tubular forms in the center are also complete flowers and are known as disk florets. Some members of this enormous and complex family have only rays, like the dandelions and chicory. Others, such as the thistle, have only disk florets. A great many, of course, have both. These florets are gathered together on a structure called a receptacle and underneath the receptacle is a circle of bracts known as the involucre. (Dale 50).
The largest family of vascular plants, with possibly 950 genera and 20,000 species, chiefly herbaceous and world-wide in distribution. (Munz, Flora So. Calif. 95).