Home > Encyclopedia of Science > Leaf

• Words to Know
• Leaf arrangement
• Blade
• Internal anatomy of leaves
• Leaves in autumn

A leaf is a plant's principal organ of photosynthesis, the process by which sunlight is used to form foods from carbon dioxide and water. Leaves also help in the process of transpiration, or the loss of water vapor from a plant.

A typical leaf is an outgrowth of a stem and has two main parts: the blade (flattened portion) and the petiole (pronounced PET-ee-ole; the stalk connecting the blade to the stem). Some leaves also have stipules, small

paired outgrowths at the base of the petiole. Scientists are not quite sure of the function of stipules.

Leaf size and shape differ widely among different species of plants. Duckweeds are tiny aquatic...