Geograph - photograph every grid square

The galls are caused by mites, which I believe(*) to be of the species Aceria cephalonea (syn. Artacris cephaloneus).

The tree itself is between the cycle path and the River Leven, not far from a NS3977 : Former railway bridge over a lade.

- - • - -

(*) The identification is according to the keys (specifically, the text) in "British Plant Galls" (2ed; Redfern & Shirley, 2011), and is based in large part on the host, the size of the galls, and the fact that the apex, where there is one, is very blunt and rounded.

The accompanying illustrations to that key give a quite different impression, suggesting that these are the galls of Aceria macrorhyncha (synonyms Aceria macrorhynchus and Artacris macrorhynchus).

Nevertheless, I have found the galls of that species to be typically much more pointed (NS3976 : Sycamore leaf with galls and tar spot fungus). It may be that the illustrations are, in this case, a little misleading, or perhaps the appearance of the galls changes as they become more mature.