While disc flowers do have petals, they are small and inconspicuous compared to the those of ray flowers. The color of disc flower petals contributes to the color of the disc. The flowering heads of some Asteraceae have ray flowers only. Wild Lettuce and Chicory are examples. Those of other species, like Thistle, have only disc flowers.
Sunflowers have both ray and disc flowers.
The flowering head, to which the ray and disc flowers are attached, is called a receptacle. On the underside of the receptacle are small leaf-like structures called involucral bracts. Their shape and color are useful in identifying the different taxa. Some disc flowers are in the form of buds and will not have opened. Collectively these bristles are referred to as the pappus.