Venation : The arrangement of veins and veinlets in the lamina of a leaf is called venation. The veins are not only the conducting channels for water, minerals and organic food/, they also provide firmness to the lamina and keep it expanded. They give rise to lateral veins, which traverse the entire lamina.
Venation is of three types : Reticulate, parallel and furcate.
1. Reticulate Venation : When the veinlets form a network the venation is termed as reticulate venation. E.g., leaves of dicot plants.
Reticulate venation has two sub-types :
(i) Pinnate or Unicostate reticulate venation: The lamina has a single principal vein or midrib extending from base to the apex. It produces lateral veins, e.g., Peepal, Shoe flower etc.
(ii) Palmate or Multicostate reticulate venation :
The lamina has more than one equally prominent or principal veins. They give rise to lateral veins connected by reticulations of veinlets. Multicostate reticulate venation has two forms.
(a) Convergent: The principal veins converge towards the apex of the lamina.
(b) Divergent : The principal veins diverge towards the margin.
2. Parallel Venation: When the veins arising from mid rib or main veins, run parallel to each other towards the margin or the apex of the lamina, venation is termed as parallel venation. Leaves of monocot plants. Parallel venation is of two sub-types :
(i) Pinnate or Unicostate parallel venation : The lamina has a single prominent vein or midrib running from the base to the apex of lamina. e.g., Banana, Canna, etc.
(ii) Palmate or multicostate parallel venation :
The lamina has several principal veins arising from the base and running towards the apex or margin of the lamina. Multicostate parallel venation has two forms :
(a) Convergent: The principal veins converge towards the apex, e.g., Bamboo, Grass.
(b) Divergent : The principal veins diverge towards the margin, e.g., Fan palm.
3. Furcate Venation : Here, the veins give off dichotomous branching. The finer branches do not form reticulum. Furcate venation is common in ferns, circeaster.