Autumn walks in wooded parks bring tree leaves in focus. Even though the leaves are dead, they can still present questions and answers about the evolutionary processes that brought them forth. Consider, for example, the shapes of these tulip poplar (Liriodendron tulipifera) leaves I picked up during a walk near my house the other evening.
I had never noticed before that the shapes of tulip poplar leaves were so variable. I am sure there are other shapes that I missed. These are the ones I noticed and picked up while trying to carry on a conversation on unrelated subjects with my wife. If I had paid any more attention to the leaves, she would have kicked me in the butt.
Can all or some of these variants be found on one tree or does each tree produce only one type of leaf? Does the shape of a leaf change during its growth? What is the functional significance of the leaf shape? Obviously, a leaf with fewer or smaller lobes would have a larger surface area for catching sun light than an equally long and wide leaf with more or larger lobes. These leaves were along a circuitous path no longer than about 2 miles, but the actual distances between the trees the leaves came from were much shorter than that. So the general environment of all the trees was the same. But, perhaps, the microhabitat of a tulip poplar determines the shapes of its leaves.