The leaf is the flattened, lateral outgrowth of the stem or the branch. It at the node and possers a bud at its axil.
It is green in color and a vegetative organ the plant. It manufactures food material and always develops in an acropetal order the stem. These are exogenous in origin developing from the swollen growing called the leaf primordia.
A. Cotyledonary leaves:
Two cotyledons occur in dicots whereas monocots have one cotyledor. The first leaves on the shoot are represented by the cotyledons. Usually, they contain reserve foods.
The cotyledonary leaves are fleshy and non-green, e.g., beans and gram. In monocotyledons, the scutellum represents the cotyledon and its function is the suction of food material from the endosperm. Cotyledonary leaves are thin and flat in Ricinus.
B. Scale leaves or cataphylls:
Scale leaves are modified leaves. They are usually brown or grey colored membranous structures that remain dry, papery or fleshy.
Mostly these are found in the underground stems. Scale leaves are also found in the aerial parts of the stem as in Casuarina, Asparagus.
C. Bract leaves or hypsophylls:
In this case, the leaves are represented by bracts which contain flower or inflorescence in their axils. Special leaves which bear floral buds at their axils are called bract leaves. These are usually small and green but in some, these are large and bright colored, e.g., Bougainvillea.
The first few leaves of a branch often differ from the other leaves and are known as prophylls. Usually there is one prophyll in monocots and two in dicots. Single prophyll in Citrus and two prophylls in Aegle are represented by spines.
E. Floral leaves or sporophylls:
The sepals, petals, stamens and carpel of a flower are modified leaves. Of these, the stamens and the carpel are considered as sporophylls as they bear spores.
F. Foliage leaves:
Normal leaves which arise from node of aerial stem as lateral appendages are called the foliage leaves. These are usually green in color. They perform vital functions such as photosynthesis and transpiration.