My not-so-little sunflower has decided to open up to the world. People often think of the large head as a single flower. It is not. Sunflowers are Asteracea (originally Compositae) family members, characterized by many tiny flowers making up one large (or small) head. In the detail photo, you can see the tiny individuals surrounded by the yellow sepals often confused as "petals".

Daisys, thistles, dandelions... many of the flowers most recognizeable to us are members of the Asteracea family. It's one of the largest!