This typical pouch gall, which is distinctive and attractive, occurs on a tiny, narrow, elongate leaf blade of a rosaceous plant. The galls are hemispherical with roughened, puckered domes; they are solitary and rarely coalescent. There are seldom more than two pouches on one leaf. Initially the galls are the same color as the rest of the leaf blade, becoming brown as they mature. Infested leaves tend to be those under shady areas or where they are less exposed to sunlight. Heavily infested plants have malformed leaves that are noticeable at a distance.
The host plant is locally known as greasewood, an evergreen shrub of the Rosaceae family; it grows in the chaparral area in California.
”- Hartford Keifer,Edward Baker,Tokuwo Kono,Mercedes Delfinado,William Styer: (1982) An Illustrated Guide to Plant Abnormalities Caused by Eriophyid Mites in North America©