Leaf and Types of Leaf

Leaf is a green expanded exogenous lateral outgrowth which arises from the node of a stem or its branches. Green leaves of the plant are collectively cold foliage leaves.

Types of leaf: 

Leaves are of two types.

I: Simple Leaf – A life with undivided lamina is known as simple leaf. Depending upon the type of leaf and degree of incision, the leaves are called pinnatifid, palmatifid, pinnatipartite, palmatipartite, pinnatisect, palmatisect.

II: Compound Leaf – It is of different types. They are –

1. Pinnate compound leaf –

• Unipinnate – Cassia, rose, murraya etc.
• Bipinnate – Acacia, Mimosa.
• Tripinnate - Moringa, Drek.
• Decompound - Parthenium, Coriander, Carrot etc.

2. Palmate compound leaf – The compound leaf gives the appearance of a palm.types –

• Unifoliate – Citrus.
• Bifoliate -  Balanites.
• Trifoliate – Oxalis, Aegle marmelos.
• Quadrifoliate – Paris quadrifolia, Marsilea quadrifolia.
• Multifoliate – Bombax, Cleome.

Venation – Venation is the arrangement of veins and veinletsin a lamina. They can be divided into reticulate venation and parallel or striate venation.

Reticulate Venation –  Veins and veinlets of a lamina. They are of different types –

1. Pinnate or Unicostate reticulate venation- Peepal, Banyan, Mangoetc.

2. Palmate or Multifoliate reticulate venation- Zizyphus ,Luffa, Castor etc.

Parallel or Striate Venation – Veins run parallel without forming reticulation. Veinlets are not conspicuous. They are of different types-

1. Pinnate – Banana.

2. Palmate – Fan Palm.

Phyllotaxy – arrangement of leaf around stem or its branches are called phyllotaxy. It can be of different types. They are –

Spiral – A node bear only one leaf and successive leaves occur on opposite sides to form two alternate rows. Example - Grass.

Opposite - Two leaves occur on each node.

(i) Opposite and superposed – Opposite and successive nodes lie one above another forming only two rows (Syzygium, Quisqualis ).

(ii) Opposite and Decussate – Opposite leaf of successive nodes lie at right angles, forming four rows. Example - Guava, Calotropis.

Whorled or verticillate – more than two leaves occur at each branch. Example- Nerium.

Modifications of Leaves: Modifications of leaves can be of different types-

1. Leaf Tendrils - Leaf or leaf part are modified into tendril like structure for climbing. They are unbranched and naked. They are of different types-

• Whole Leaf Tendrils - Whole leaf is modified into tendril. Example- wild pea.
• Leaflet Tendrils - Upper leaflets are transformed into tendril. Example- sweet pea, edible pea.
• Petiolar Tendril - Petioles are elongated and sensitive to function as tendril. Example - Nepenthes.
• Rachis tendrils – Rachis and petiolules are convert to tendril. Example-Clematis.
• Rachis Tip tendril - Tip of rachis is modified to form tendril. Example- Lentil.
• Leaf tip tendril - The leaf apices are elongated and sensitive to function as tendril. Example - Glory lily.
• Stipular Tendrils – The tips of the adnate stipules produce tendrils. Examples- Smilax.

2. Leaf Spines – Leaf is converted into prickles. Example- Opuntia , Asparagus, Barberry.

3. Leaflets Hooks - Terminal leaflets are modified into curved hooks for climbing. Example- Bignonia.

4. Leaf Roots – One leaf of each node is transformed into roots for balancing on water. Example- water fern.

5. Phyllodes – Phyllodes are flattened petioles and reaches which has taken over the function of lamina. Example - Australian Acacia.

6. Leaf Bladders – Some of the leaf segments of aquatic insectivore. Example-Cyclops, Utricularia.

7. Leaf Pitchers – Lamina or whole leaf is modified into pitcher to catch insects. Example- Nepenthes.

8. Hygroscopic Appendages – Leaves are modified into hygroscopic appendages. Example - Tamarix.

Eleventh Grade

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