The way in which the midveins, veins and subveins of the leaves are arranged is called venation. There are two types of veins. These are-
1. Reticulate venation: When the midveins, veins and subveins of the leaves are connected to form a net-like structure, it is called reticulate venation. Dicotyledonous plants have reticulate veins. Among monocotyledonous plants reticulate veins are seen in kachu, kumarika etc. There are two types of reticular venation.
(i) Unicoil reticular venation: A reticular venation that has only one central vein along with veins and splenic veins is called unicoil reticular venation. For example, mango.
(ii) Multivenous reticular venation: A reticular venation that has more than one vein like the central vein is called multivenous reticular venation. Polycoccal reticular venation is of two types. These are-
Convergent multiveinal reticulate venation: In the multiveinal venation in which several main veins arise from the base of the leaf blade and meet at the tip of the leaf is called convergent multiveinal reticular venation. For example – kul or plum.
Divergent multiveinal reticulate venation: The multiveinal venation in which more than one main vein originates from the base of the leaf blade and extends to different ends of the leaf is called divergent multiveinal reticular venation. For example, papaya.
2. Parallel venation: If the veins of the leaves are arranged parallel without being connected to each other, it is called parallel venation. Monocots have parallel veins. Among dicotyledonous plants, parallel venation is seen in Sultana chapa plants. There are two types of parallel veins.
(i) Monovenous Collateral Venation: A parallel vein that has only one central vein is called Univenous Collateral Venation. For example, bananas.
(ii) Multivenous parallel venation: A parallel venation that has more than one major vein is called multivenous parallel venation. There are two types of multivenous parallel venation.
Convergent multiveinal parallel veining: In the multiveinal venation in which more than one main vein originates from the base of the leaf blade and joins at the top of the blade is called convergent multiveinal parallel veining. For example, bamboo.
Divergent multiveinal parallel venation: The multiveinal venation in which more than one main vein originates from the base of the leaf blade and spreads to different ends of the blade is called divergent multiveinal parallel venation. For example, rhythm.