Look at this fungal (or maybe not?) infection on these leaves on the oak tree in my backyard.
@vector Perhaps a kind of leaf galls?
@nox I have approximately "Magic School Bus Level" knowledge of plant biology. So, maybe?
@vector Haha! It’s a weird growth that forms as a reaction to something irritating the leaves, usually mites or bugs nibbling, but could be other things too.
@nox That sounds right! I saw some little sugar ants biting at the underside of the leaf at one of the swollen sites.