Looks like the work of gall insects. They burrow into the leaves and cause the tissue to swell. That becomes their home.

Forgot to mention, definitely looks like London Plane Tree, Platanus species.

IMHO ... gall damage to leaves is usually superficial ... and not really harmful to the tree ... not to mention.. the leaves usually fall off most trees ... as long as the leaves stay green... they continue to do their normal jobs ... i would NEVER treat a deciduous tree for such ....

some of the galls ... are actually beneficial insects ....

when it all boils down ... it looks horrible.. but odds are ... its irrelevant to the tree ..

the hole in the leaf is most likely unrelated ...

ken

ps: this is where someone chimes in .. and says that there is some local AU hybrid gall of death ..... that is devouring everything on the continent.. and that i am an idiot ... wish me luck with that ... lol

I'd say galls, too. What does the underside of the leaf look like?

Ken, would you mind sharing the information about the beneficial insects and plant galls? I'm serious....I've not heard of or am not remembering such a thing and would like to be educated.