On Quercus palmeri (Palmer's oak). Palmer's oak is the only oak species on which this gall grows.

Quercus palmeri grows mostly in disjunct populations in southern California, but small populations extend into northern California. A recent study has concluded that Palmer's oak is the oldest living plant in California, that at least one population is a single clone, and that at one time this oak was more widespread but due to climate change its populations have shrunk. This is interesting in light of the fact that Palmer's oak has a number of wasps that gall it that don't also gall other oaks in the "intermediate oak" group in California. At least a few of the cynipid wasps that gall Palmer's oaks have not been described.