In the grounds at Ackworth School yesterday, I noticed some striking leaves on an ornamental maple tree.
Maple leaves
Only a section of the tree is affected. The leaves on most of the tree are completely green.
Maple leaf
I suspect that the markings are the work of a fungus that is taking advantage of the weakening state of the leaves as they begin to shut down for autumn. It will be interesting to see how the infection develops in the next week or two.