There are many stem variations in plants. Some variations are forms of food, such as potatoes and asparagus. Others are forms sold in dormant condition for introduction into the landscape as new plants, such as dahlia tubers and tulip bulbs. The main function of leaves is food production for the plant. Leaves have evolved into many shapes and sizes, reflecting adaptations to the environment.
Leaves are most commonly flat, broad and green.
This maximizes their function of absorbing sunlight and transforming it into food. This protective layer reduces the exchange of water and gases and prevents some disease-causing organisms from entering. New seedlings and houseplants should be gradually moved into sunlight. Sunscald is the result of too much water being lost from heat and wind. This waxy layer in some instances makes it difficult for herbicides to stick to and enter the leaf.