The agamic galls are ovoid; they occur in clusters and are embedded in the bark on the oak tree-trunk; eventually only the empty galls or sockets persisting. They are usually found in callus tissue that forms around wounds on the main trunk.

[The sexual galls are small and inconspicuous, formed in buds in leaf axils and hidden by the bud scales]

The agamic barnacle galls (Andricus sieboldii and testaceipes) also form on oak tree trucks, usually close to the ground, but are conical and ridged.

Photograph the gall on oak, and note the host species

native oak trees

Locally common (British Plant Galls, Redfern & Shirley, 2023)

occasional; possibly under-recorded.  Although the remains of old galls are occasionally found and may not be uncommon, fresh galls have not been seen in VC55 to date (Spring 2025).

See British Plant Galls (Redfern & Shirley, 2023) and Bladmineerders (Plant Parasites of Europe) webpage