Can't seem to pinpoint what tree this is from. Found on a tree in Philadelphia, PA, though it may be ornamental and not native... I should add, while I don't have a picture, the leaves were serrated, and roundish in overall shape.
One of the oaks in Quercus sect. Cerris, a group of oaks from Europe and Asia. Perhaps the most likely of this group to be planted in PA is Sawtooth Oak Quercus acutissima; see pic here: Frilly acorn for comparison.
