Erineum galls on a maple leaf, produced by Eriophyidae mites.

Leaves from the maple tree (Aceraceae family) can become infested with what are known as galls (the pink blotches in this image). Galls are abnormal plant cell growths and they are often caused by eriophyid mites (Eriophyidae family). Galls are sometimes referred to as plant tumours. Width of image 1.5 centimetres