What Is This?

I think this is a southern red oak leaf, but I'm thrown off because there are only three lobes. I've always thought of southern red as having five.

Thanks.

There are 3 lobed southern reds oaks. They're not dimorphic, the 3 lobed leaves occur on different trees than the 5-7 lobed ones. The 3 lobed leaves are obovate and the 5-7 lobed are ovate.

What you have there also looks like it could be Q. marilandica, Black Jack Oak, but the petiole is a bit too long. Maybe a hybrid?

My vote is Q. falcata.

I don't know about your southern oaks, but ours seem to 'hybridize' quite a bit. Red-scarlet-black-etc.