Leaves - Photo by Giovanni Ussi - Foglie 22

SEM image of Nicotiana alata leaf's epidermis, showing trichomes (hair-like appendages) and stomata (eye-shaped slits, visible at full resolution).

Leaves can have different shapes. The part of biology that studies the shapes of things is called Morphology

A leaf is a green above-ground plant organ. Its main functions are photosynthesis and gas exchange. A leaf is flat so it absorbs the most light, and thin, so that the sunlight can get to the chloroplasts in the cells. Most leaves have stomata, which open and close. They regulate carbon dioxide, oxygen, and water vapour exchange with the atmosphere.