I believe, but I’m not totally sure that I have Chestnut Oak (Quercus prinus) and Swamp Chestnut Oak (Quercus michauxii) growing in my backyard. The two leaves on the left I think are Swamp Chestnut Oak. The leaf on the right (which is showing it’s underside, whereas the others are showing their uppers) I think is Chestnut Oak. I’m not the only one to confuse the two: confusion of the two species mentioned on Wikipedia.
1. These closely related species have wavy leaf margins. Why? I have no idea.
2. Two of these leaves have what appear to be galls. What are galls? They are abnormal growths on plants. They come in a huge variety of shapes and sizes (see this gallery of galls). Many (including these ones it appears) are caused by insects depositing eggs in the plant. Somehow the local plant tissue is reprogrammed to grow the gall. The gall provides the young insect with food and shelter. Does the plant get anything in return? I’m not sure.
3. It appears that the gall on the lower leaf has a leaf mine emerging from it. In other words, it looks like the young insect (or maybe it was a mite) emerged from the gall and tunneled through the leaf, eating as it went. In the enlargement I’ve highlighted the path of the mine from the gall to the place where the insect mined in a little loop.
Check out this Q&A about galls and leaf mines.
4. My kids insisted that I show this gall detail, and for good reason! It is very intricately marked with light and dark squiggles. What could cause this? Does the marking serve a purpose? What mathematical models describe the marking?
5. Some leaf feeders skeletonize the leaf. They leave behind only the veins. These patches of skeletonization probably happened on the living leaf. Once leaves die and start to decay on the forest floor, they often undergo more skeletonization.
6. Some leaf-feeders eat holes in the leaf. Birds often find insects to feed on by looking for leaf damage, or maybe even by looking for the shadows of damaged leaves (thence finding the damaged leaves themselves and finally the invertebrate doing the damage).