This is a leaf on an unknown vine that is growing among a large patch of wineberry, an invasive and nonnative bush that produces edible berries. This patch just happens to be in my yard. I noticed this leaf a few days after my son Will and I picked the plants clean of their berries. (We made jam for the first time and, boy, is it good.)
The vine may be a wild grape, but I’m not positive. It is the only such vine growing among the wineberry, so far as I can tell. The leaf appears to have red double-sided daggers sticking out the top and bottom. Perhaps it is a growth coming from either direction. I have no idea. It is the only leaf that looks like this. Of the thousands of leaves surrounding it, this is the only one with this phenomenon.
So, any ideas??
Here are a few more photos.