Oak apple

Oak galls on a Pyrenean oak (*Quercus pyrenaica*) in León, Spain.

Oak apple or oak gall is the common name for a large, round, vaguely apple-like gall commonly found on many species of oak. Oak apples range in size from 2 to 4 centimetres (1 to 2 in) in diameter and are caused by chemicals injected by the larva of certain kinds of gall wasp in the family Cynipidae.^[1]

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