The shapes of plane leaves vary considerably. The edges of leaves may be smooth or jagged. The leaf blades may be undivided(simple), or they may be divided (lobed) in various ways. Some leaves may be made up of separate leaflets. The commonest types of leaf shape are show below
Also, there is another reason that the shape of a tree’s leaves are a response to the tree species’ long term ecological and evolutionary histories. An ecosystem’s limiting factors may also modify the finished form and shape of a tree’s leaves. Understanding of the “logic” behind the varied forms of leaves is facilitated by a firm grasp of the precise functions a leaf must accomplish.
1. A leaf must “capture” sunlight for photosynthesis (and as it does this it may also absorb a great deal of heat!)
2. A leaf must take in carbon dioxide from the surrounding air via pores (called “stomatae”). This carbon dioxide is also needed for photosynthesis. When these leaf stomatae are open to allow the uptake of carbon dioxide, water from inside the leaf is lost to the atmosphere.
The leaf, then, is affected by these balancing acts: enough sunlight and carbon dioxide to run photosynthesis, but not too much associated heat absorption or water loss.
The leaves themselves may be arranged on the plant in different ways, and this is usually standard for any given type of plant. A leaf arrangement which has single leaves at each level is called alternate. Leaves arranged in pairs are known as opposite. Opposite leaves may all face the same way, or each pair may be at right angles to the pair below.
Some plants have all their leaves in a ring at the base of the stem. This is known as a rosette.