A leaf is an organ of a vascular plant and is the principal lateral appendage of the stem. The leaves and stem together form the shoot. Leaves are collectively referred to as foliage, as in “autumn foliage.
Typically a leaf is a thin, dorsiventrally flattened organ, borne above ground and specialized for photosynthesis. In most leaves, the primary photosynthetic tissue, the (palisade mesophyll), is located on the upper side of the blade or lamina of the leaf but in some species, including the mature foliage of Eucalyptus, palisade mesophyll is present on both sides and the leaves are said to be isobilateral.