Eriophyes pseudoplatani[2] Aceria pseudoplatani causes the sycamore felt gall that is found on the leaves of sycamores (Acer pseudoplatanus) or Norway maple (Acer platanoides),[3] and is caused by an acarine gall-mite.

The gall forms a bulge on the upper epidermis, where the pigment colour is usually light yellow to start with and brown later on in the year.

The appearance on the lower epidermis is a concavity with cream- or white- coloured felt-like mat that later turns brown.

[3] The size of the felt-like patches is variable, and they may appear from late spring onwards.

[5] The sycamore felt gall is quite common, is widespread throughout the United Kingdom[6] and is also recorded in Poland, Belgium, and Germany.