Leave it to the Leaves

By Susan Deo

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Have you ever lain down under a tree on a sunny summer day and looked up at the leaves above you? Did you notice how each leaf has oriented itself for maximum sun exposure? Leaves are the food factories of flowering plants and ferns, as are the modified leaves, or needles, of pine and fir trees.

The chloroplasts, tiny structures in the plant cells that contain chlorophyll, absorb the sun’s energy and use it to combine water and carbon dioxide into food the plant uses to grow and reproduce. Tiny openings in the leaves, called stomates, allow gases in and out of the leaf: in goes the carbon dioxide to help manufacture food, out goes the oxygen “waste.” Water also evaporates through these openings. This helps cool the plant (and the air around it) and helps pull water and nutrients up through the roots to the leaves.

Leaves are amazing little factories. But they are also works of art and efficiency. Some leaves are bright green, some dark or gray. Some leaves feel firm like leather, others soft like velvet. Some leaves are as smooth as silk, others as fuzzy as a blanket. There are rounded leaves and oblong leaves, and leaves with lobes or even “teeth” around the edges. Many of these are adaptations that help the plant survive in its habitat. A cactus, for example, has leaves modified into spines to help prevent water loss. They are so narrow and hard they don’t even have chloroplasts, though. The chloroplasts are in the stem instead and that is where food is made.

Southern California plants have found many ways to adapt to our dry climate. When water is scarce, leaf design can play a major role in conserving water. Small leaves have less surface area, so they lose less water. Coyote bush is a good example of small leaves, so is California sagebrush. Waxy and/or curled leaves can also reduce evaporation. Lemonade berry bush has leaves like this. If a plant loses its leaves when there is a drought, it will prevent excessive water loss as well. California bush sunflower and California sagebrush have evolved exactly this adaptation. Light colored or “hairy” leaves absorb less of the sun’s energy, losing less water also. White sage is a good example of this. White sage will also lose its leaves if the weather gets dry.

So the next time you are out on the path, take a look at some of the amazing leaves around you and see if you can figure out why they look and feel the way they do.