What is the upper surface of the plant leaf called?

The upper surface of a plant leaf is called the upper epidermis. In botanical terminology, it is also known as the adaxial epidermis, meaning the side oriented toward the stem or central axis of the plant.

The upper epidermis is usually a single layer of tightly packed cells. It helps protect the leaf from physical damage and reduces water loss, often with a waxy cuticle on its outer surface. Unlike the mesophyll beneath it, these epidermal cells generally contain few or no chloroplasts in ordinary leaves.

Beneath the upper epidermis lies the palisade mesophyll, where many of the leaf's chloroplasts are concentrated and much photosynthesis occurs. The lower epidermis is called the abaxial epidermis and commonly contains more stomata than the upper surface, allowing gas exchange while limiting excessive water loss.

A common exception occurs in floating leaves: because their lower surface rests against water, many or all of their stomata may be located on the upper epidermis instead.