The main photosynthetic organ of most green plants, consisting of a lateral outgrowth from a stem and comprising *
lamina , *
petiole , and leaf base. (See
lamina for the different kinds of leaf shapes and leaf margins.) There are usually a great number of leaves on any one plant, although these may be lost in the colder or drier months in deciduous plants. A leaf typically consists of conducting tissues and photosynthetic cells (the *
mesophyll ) often differentiated into *
palisade and *
spongy mesophyll , surrounded by *
epidermis. The epidermis is perforated by *
stomata, usually more numerous on the abaxial (lower) side of the leaf. The epidermis is usually covered by a waxy cutinized layer termed the *
cuticle. This prevents excessive water loss by transpiration. In many plants, however, leaves may be reduced or even absent, as in many xerophytes. Sepals, petals, and bracts are considered to be modified leaves and many believe the stamens and carpels are also derived from leaves. See also
microphyll ,
megaphyll.
