Other examples and also Al Stohlman used to do Dogwood with 5 petals. They may have four five or six petals. Technically they are not flowers petals but somethings called bracts. In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often (but not always) different from foliage leaves, for example being smaller, larger, or of a different color or texture.
The five bract dogwood is the Provincial Flower of British Colombia in Canada. Al Stohlman had a ranch at Cache Creek,British Colombia and the reason why he included five bract in his dogwood designs as well as four!