Looking a bit like mushrooms, these galls on the leaves of this white oak in Green-Wood are the results of yet another Cynipidae gall wasp, Phylloteras poculum. Mine was the third iNaturalist report of this species. I tracked the species down on bugguide.net. Bugguide.net doesn’t have an image of the actual (tiny) wasp.
So this one oak tree has a minimum of three different galls on it.