Parts of a leaf

These are the basic parts of a leaf:

Petiole

This is the stalk which may attach the leaf to the stem; some leaves attach directly and don’t have petioles. Leaves attached via a petiole are called ‘petiolate’, leaves which attach directly are called ’sessile’.

Lamina

This is the main portion of the leaf, also called the ‘blade’. The edge of the lamina is usually referred to as the ‘margin’ of the leaf. The cells of the lamina, particularly those near the surface of the leaf, contain a high volume of chloroplasts, which carry out photosynthesis.

Midrib

This is the main vein which travels along the centre of the leaf and contains the phloem and xylem transport vessels.

Veins

Smaller veins veer off from the midrib to ensure that the transportation system of the plant extends to all parts of the leaf. The sections between the leaf veins are known as ‘inter-veinal’ areas.

Stomata

These are tiny pores underneath the leaf which allow gases to enter and leave the leaf. These include the gases which are vital for photosynthesis and water vapour. If the plant is in drought conditions the stomata will close to retain water within the plant. While this is useful in the short term, it cannot carry on long term as the plant will not have access to carbon dioxide and will, therefore, be unable to photosynthesise to produce the energy it needs to survive.

Leaf adaptations

Leaves have evolved in many different ways to help plants survive in various environments. These are some examples of leaf adaptations:

• Spines – plants which have adapted to dry environments (such as cacti) may have spines instead of leaves, which reduce water loss and protect the plant from grazing animals.
• Tendrils – these adapted leaf stalks or leaflets twine around anything they touch to help the plant climb up. Clematis and sweet pea plants have tendrils.
• Traps – insectivorous plants may have adapted leaves to trap their prey, such as the sticky leaves on sundews or hinged leaves of the Venus flytrap.
• Bulbs – bulbs and corms are mainly made up of adapted leaves, which are packed densely together underground and store food for the plant’s future growth.
• Hairs – leaves which have adapted to become hairy generally originate from hot climates where the hairs help to reduce the amount of moisture lost by maintaining higher humidity levels around the leaf surface. For example, some native Mediterranean plants, such as lavenders, have very hairy leaves.

Monocotyledon leaves

The leaf shown above is an example of a leaf from a dicotyledon; a plant which has two ‘seed’ leaves. Monocotyledonous plants have just one ’seed’ leaf and the ‘true’ leaves differ in appearance in two main ways. Firstly the veins (including the midrib) run along the length of the leaf and are parallel to each other, rather than in a spreading network of veins originating from a midrib. Secondly they are all sessile, attached to the stem in a sheath like manner. Grasses and bulbous plants are examples of monocotyledons.