Leaves occur in various arrangements in plants. All plants seem to have leaves on branches to normal folks. We, botanists should see it different though. Many plants have several leaves in a branch which called leaflets and the whole branch is called as a leaf! These are called compound leaves. So basically there are two types of compound leaves in a broader sense. A compound leaf may be either pinnately compound or Palmately compound.
Before actually getting into the topic, one should know what s simple leaf look like. To be simple, a simple leaf will contain only one leaf that is attached to the stem by a petiole. Whereas a compound leaf will have many leaf lets attached to a stem by means of a petiole. The branch that contains the leaflets are called a rachis.
Pinnately compound leaves
These leaves contain leaflets arranged in opposite arrangement on the rachis (the extended petiole). The leaflets may be evenly paired or oddly paired. In the evenly paired pinnate leaves, the leaflets are arranged in an opposite manner and the rachis ends with two leaflets and is called Paripinnate. In oddly paired pinnate leaves, the leaflets are arranged in opposite fashion with a trailing leaf at the anterior end of the rachis and is called imparipinnate.
The leaves may be of three types based on the number of times of pinnation as follows,
Single leaflets are present on the rachis in opposite fashion.
Example: Azadirachta indica
When the single leaflets of the unipinnate leaf gets replaced with unipnnate leaves themselves becomes bipinnate leaves.
Example: Mimosa pudica
When the single leaflets in the unipinnate leaves get replaced with bipinnate leaves, it is called as tripinnate leaves!
Example: Moringa oleifera
Palmately Compound Leaves
These are a form of compound leaves that appear as a single leaf but appearances may be deceptive! Multiple leaflets arise from a common point that is at the end of the petiole. Based on the number of such leaflets, they are classified as follows,
These leaves contain a simple leaf blade as a normal leaf with a winged petiole. Examples: Citrus limon, Citrus maxima
These leaves will contain two leaf blades attached to the petiole at a single point.
Example: Bauhinia Yunnanensis
These appear to be three leaves originating from the anterior end of the petiole.
Example: Clover leaves are mostly trifoliate and rarely quadrifoliate.
Four leaves would be fused to a petiole and appear to be a single leaf.
Example: Oxalis, Marsilea
When more than four leaflets are attached to a petiole to form a single leaf, it is called a multifoliate palmately compound leaf.
Example: Baobab, Umbrella plant.