content: They aren't petals - you are actually seeing many flowers! Daisies are in the Asteraceae family, also called Compositae. They have composite flower heads called capitula or pseudanthia. Each of the "petals" is a flower (ray flowers) and in the middle are more flowers (disc flowers). Furthermore, the most common number of petals is 5 in dicotyledonous (or its multiple); the family Brassicaceae have 4 (they aren't called also Cruciferae for nothin'!). Monocotyledons have 3 or 6 petals. Some plants defy these rules of thumb, eg. Trientalis europaea has usually seven petals and Ranunculus ficaria may have nine... (I'm on a commenting roll in this thread, it seems.)