The arrangement and distribution of veins on the leaf lamina are known as venation. Veins from the structural framework are made up of conducting tissues i.e., xylem and phloem.
Three are three main types of venation-
Reticulate- When veins form the irregular network on the leaf lamina, this is known as reticulate venation. It is a characteristic feature of the dicotyledons.
Unicostate reticulate- A leaf with single midbrain and costa is called unicostate reticulate. Example-Eugenia (Jamun)
Multicostate reticulate-When two or more principal veins are derived from a single point. For example- Zizyphus (Beri)
2. Parallel venation- When veinlets are parallel in distribution, such a venation is known as parallel venation. It is a characteristics feature of the monocotyledons. It is of two kinds-
Unicostate parallel- The lamina of the leaf has one single midrib, from which arise lateral veins which run towards the margin, e.g. Banana
Multicostate parallel-Several veins run parallel to one another,e.g. Bambusa (Bamboo)
With few exceptions, their Monocotyledons like Dioscorea shows reticulate venation and Calophyllum (Dicotyledon) shows parallel venation.
Final Answer-
The pattern in which veins and veinlets arrange themselves on the leaf lamina describes venation. It is of two types reticulate venation and parallel venation.