Phylloteras poculum, no common name, is a tiny gall wasp. They lay their eggs on a white oak leaf, and the tree responds by building this structure, which envelops the egg. The larva inside is protected from the elements, including, to a certain extent, predators, and has plant material to eat in there.
Backyard and Beyond 
At first glance it looks like the plant is trying to attract something which will eat the wasp egg or larva. It’s as beautiful as a flower. I wonder if any bug takes advantage of this packaged food. Ants, maybe?
Some galls seem to exude treats, with ants, bees, flies crawling over them. A future post will highlight this.