Oak Apple Gall - Amphibolips cookii
These green, spherical galls form on the buds of oak (Quercus sp.). This one was 20-25 mm diameter.
I considered that this gall could be Amphibolips quercusinanis, but the galls in that species of wasp form on leaves during late spring. So, A. cookii seemed more likely as they grow on buds and mature in September.
Habitat: Oak tree growing along the coast.