You can see why I 'm a County Agent and not a poet. Even though my poetry is bad, I have a good subject. Leaves make an interesting study of the Master Designer's handiwork. The leaf's main function is to catch sunlight and turn this energy into sugars for food. Leaves growing in shade may be even larger to catch more light.
Some plants have thicker leaves, like magnolia.
This will allow them to intercept as much light as possible and to prevent other plants growing under them. Leaves are also important in our environment. While on the plant, they provide cooling, shade, and water, air, and noise pollution control. This system allows air to get into the leaf to provide the carbon dioxide necessary for photosynthesis. Water is also important.