This is the fourth dogwood to be featured on BPotD. By revisiting the other three, you can get some idea of the diversity of floral structure within the genus: Cornus chinensis, Cornus macrophylla and Cornus 'Eddie's White Wonder'. The white petal-like structures seen here are actually modified leaves called bracts. A plant in a closely related family, the Nyssaceae, also has subtending bracts: Davidia involucrata 'Sonoma'.
The fruits of kousa dogwood are edible (see the Plants for a Future entry on Cornus kousa), but I wouldn't eat them in quantity. Apparently, members of both the Cornaceae and Nyssaceae share the characteristic of being aluminum accumulators (source: description of “Cornaceae + Nyssaceae” on the Cornales page of the Angiosperm Phylogeny Group site).