Pinnately Compound Leaf Notes

Compound Leaves

Compound leaves are a type of leaf structure, where the lamina is divided into multiple leaflets or pinnules. In the case of pinnately compound leaves, the leaflets are attached to a common axis, called the rachis, which is the midrib.

Leaves can be divided into two types based on the division of the lamina:

  • Simple Leaves - which are undivided, or have incisions that do not reach the midrib
  • Compound Leaves - which have their lamina separated into multiple leaflets

Compound leaves are of two types:

Pinnately Compound Leaves - Here, leaflets are arranged on a common axis known as the rachis. The leaflets, or pinnules, are arranged in an opposite manner and the rachis acts as the midrib. An example of a pinnately compound leaf is the Neem leaf.

Palmately Compound Leaves - Here, the leaflets are attached at a single point at the tip of the petiole. For example, the Silk Cotton tree.

Axillary buds are not present in the axils of leaflets.

Types of Pinnately Compound Leaves

On the basis of the arrangement and number of leaflets, pinnately compound leaves can be classified into the following types:

Paripinnate - It has an even number of leaflets attached in pairs on the rachis, with the two leaflets at the end. For example, Tamarind.

Imparipinnate - Leaflets are attached in an opposite manner and an odd number of leaflets are present, with a single leaflet at the apex of the rachis. For example, Neem.

On the basis of the number of times they are divided, pinnately compound leaves are divided into the following types:

Unipinnate - These are also known as simple pinnate. In this type of leaf arrangement, leaflets are attached directly to the rachis in an alternating pattern, for example Cassia.

Bipinnate - In this type of arrangement, the primary rachis is branched and leaflets are attached to the secondary rachis, for example, Acacia.

Tripinnate - Here, the secondary rachis is further divided into tertiary rachises, to which leaflets are attached, such as in the case of Moringa.

Decompound: These leaves are composed of three or more leaflets. For example, coriander.

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