Biology Today — January 2018

Venation

• The arrangement of veins and veinlets in the lamina of a leaf is called venation. Depending upon the distribution pattern
  of veins, venation is of three types:

Reticulate venation

The vein and veinlets are distributed irregularly to form a network.

Usually found in dicots except Calophyllum, Corymbium and

Eryngium.

Parallel venation

Veins run parallel to each other and a network is absent. It occurs in most monocots except Smilax, Colocasia, Alocasia, Dioscorea.

Convergent

• Principal veins converge towards
  the apex of lamina, e.g., Zizyphus,
  Smilax.
  Principal veins

Veinlet

reticulation

Fig.: Multicostate convergent

venation of Zizyphus

Divergent

• Principal veins diverge towards
  margins, e.g., Castor, Luffa.
  Veinlet reticulation
  Principal veins

Fig.: Multicostate divergent

venation of Luffa

Unicostate

• The single principal vein or midrib
  extends from its base to apex. It
  gives rise to lateral veins along
  its entire length like the plumes
  of a feather, e.g., Ficus religiosa.

Veinlet

reticulation

Midrib

Lateral veins

Fig.: Unicostate reticulate

venation of peepal

Furcate

• Veins branch dichoto-
  mously and the branches do
  not form a reticulum. It is
  most common in ferns, e.g.,
  Adiantum and occassionally
  in higher plants, e.g.,
  Circeaster.

Stalk

Veins

Fig.: Furcate venation in

Adiantum

Types of Venation

Unicostate

• Single principal vein present and several lateral veins run
  parallel to one another, e.g., Canna.

Parallel veins Midrib

Fig.: Unicostate parallel venation of banana

Multicostate

Several principal veins arise from base of the lamina. Based upon

orientation it is of two types.

Convergent

• Principal veins converge
  towards the apex, e.g.,
  bamboo.

Lateral

converging

vein

Divergent

• Principal veins proceed
  towards the margins, e.g.,
  Livistonia.

Parallel

diverging

veins

Fig.: Multicostate convergent

venation of bamboo

Fig.: Multicostate divergent

venation of fan palm

Multicostate

A number of principal veins arise from base and reach to margins. They give rise to lateral

veins connected by reticulations by veinlets.