Fig 1
DESCRIPTION: Located between the midrib and the central vein this small gall develops under the lower epidermis of the leaf and when it emerges it has two flaps of valve-like tissue which usually remain until the gall is fully developed. Starting green and spherical the outer surface darkens and becomes spotted pinkish red or, in some instances, green or brown. The wasp that is the causal agent has both bisexual and agamic generations and, as a result, forms two distinct galls, the Oyster Gall and the April-Bud Gall. DISTRIBUTION: Widespread throughout Britain. HABITAT: On the underside of leaves on various Oak species.

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