Many of these leaves were on the forest floor. They look to be from different plants.
Yet they are both leaves from the common English Ivy. There are several varieties, though probably all of the common (and invasive) types have this funny characteristic. In fact, as a further surprise, I learned that the smaller, simpler one on the right comes from older sections of vine. Apparently, the mature branches of this ivy are the ones that have flowers, fruit, and this simpler leaf. As a check, I looked at some leaves still on a live vine, and saw both types of leaf close to each other. So, the old and new branches can even be side-by-side. Anyway, once again, something common and usually overlooked actually has some interesting aspects.
— Jon