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