Leaves
Absorbing Light
Leaves are usually flattened structures that act like solar panels, capturing the sun’s energy so plants can make food through photosynthesis. Chlorophyll, the green pigment in most leaves, helps plants absorb sunlight.
Leaf Parts
The parts of leaves are visible on the front (left) and back (right) of this grape leaf (Vitis sp.). They include the (1) petiole, (2) lamina, (3) midrib, (4) veins, and (5) cuticle. Photo by Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
An individual leaf has many smaller parts.
- Petiole attaches the leaf to the stem. Petioles can be long or short, thick or thin.
- Lamina is the leaf’s main, flat, green “blade” where photosynthesis primarily occurs.
- Midrib is the primary vein. It supports the leaf from the middle and helps it keep its shape.
- Every leaf has a system of veins. These small tubes move nutrients and water from the roots throughout the leaf and carry food created during photosynthesis to the stem, where it can travel to other parts of the plant.
- Cuticle is a waxy, protective outer layer covering the lamina. It helps reduce water loss and protect the leaf from the elements.
Leaf Adaptations
Adaptations are changes in life forms over time that improve their potential to survive. The size, shape, texture, and color of leaves help protect plants in many ways, and sometimes the same leaf adaptations can serve more than one purpose, depending on where a plant lives. For example:
- Hairs and fuzz on leaf surfaces help plants survive in several ways in dry environments. They trap moisture and increase humidity around the surface of the leaf and stem. They also diffuse light and create shade on the surface of leaves. Some dry habitats can also experience very cold temperatures, and hairs or fuzz protect the plant from frost.
The hairs on Echeveria ‘Doris Taylor’ help it survive in dry environments. Photo by Sandy Masuo. | The Huntington Library, Art Museum, and Botanical Gardens.
- Spines protect plants by making it difficult for animals to eat them.
The spines on the finger cactus (Mammillaria longimamma, top) and crown of thorns (Euphorbia milii, below) help protect the plants from hungry animals. Photos by Ivan Garibaldo, John Trager, and Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
- Waxy coatings (epicuticular wax) in dry environments provide sun protection and prevent plants from drying out. In tropical habitats, where it rains often, waxy coatings on leaves help repel water.
The waxy coating on Dudleya pachyphytum provides sun protection in dry environments. Photo by Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
- Soft, delicate leaves are common in plants that live in water because they do not need to cope with wind, frost, and arid conditions.
Water lilies (Nymphaeaceae) have soft, delicate leaves. Photo by Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
- Small and narrow leaves reduce the surface area of a plant, so it loses less water through evaporation compared to large leaves.
The boojum tree (Fouquieria columnaris) is a desert plant with small leaves. Photos by Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
- Thick, fleshy leaves help plants store water. They are common in succulent plants that live in dry habitats. Other plants from dry habitats store water in the tissues of their stems and roots.
Aloe camperi has thick leaves filled with water. Photos by John Trager and Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
- Large, dark leaves are adaptations to low light and ample water. In tropical areas, almost no sunlight reaches the forest floor because the many layers of foliage block it out, so leaves grow large, dark green, and angled to capture any rays of light filtering through the thick canopy. Their dark pigment also helps them absorb as much light as possible.
The dark green leaves of Anthurium kamemotoanum (left) and Anthurium warocqueanum (right) are adapted to low light. Photos by Max Tepper and Jamie Pham. | The Huntington Library, Art Museum, and Botanical Gardens.
- Light-colored leaves reflect more sunlight and heat than dark leaves. This helps protect plants from overheating, so they are common in desert plants. Aquatic plants that float on the surface, where sunlight is abundant, may also be lighter green than plants that live deeper in water.
The light leaves of white sage (Salvia apiana) help protect it from overheating in hot, dry environments. Photo by Max Tepper. | The Huntington Library, Art Museum, and Botanical Gardens.
Coauthors
Victoria Gonzalez is digital learning specialist at The Huntington.
Sandy Masuo is botanical content specialist at The Huntington.
Contributors
Rebecca Kon is a former curriculum development specialist at The Huntington.
Reviewers
Dora Dalton is a freelance writer and editor.
Kathy Musial is senior curator of living collections at The Huntington.
Sarah Thomas is school programs and partnerships manager at The Huntington.
John Trager is Bernie and Miyako Storch Curator of the Desert Garden and Collections at The Huntington.
