The flower of the Flowering Dogwood (Cornus florida), is the state tree of Missouri. The flowers are apetalous(i.e. lacking petals). The showy part of the flower, just beginning to unfold here, is actually the sepals, not the petals. The Missouri Department of Conservation has more information about the flowering dogwood.
Three other dogwood species are native to Missouri: Rough-leaf Dogwood, Alternative Dogwood, and Gray Dogwood. They aren't as showy as the flowering dogwood, but are still beautiful plants. And while we think of dogwoods as understory forest trees, the Rough Dogwoods is actually found in prairies, old-fields, and other open areas.