Alternate

In this arrangement, leaves are arranged alternatively on the stem with one leaf per node in a straight line.

Opposite

Here, two leaves arise from a single node in opposite fashion.

Spiral

Only one leaf is present per node as in alternate arrangement. But, the leaves are arranged as a spiral which would be visible if you look down at the apex of the stem.

Whorled

Multiple leaves arise from a single node and each nodes are separated by huge internodes.

Other arrangements include Subopposite and Deccusate.

Subopposite

Here, the leaves are arranged in such a fashion that they are neither spaced far enough to be considered as alternate nor exactly opposite enough to consider as opposite.

Deccusate

This is where two leaves arise from a same node (opposite) in each nodes. The pairs are placed in right angles to each other.

Leaves occur in various arrangements in plants. All plants seem to have leaves on branches to normal folks. We, botanists, should see it differently though. Many plants have several leaves in a branch called leaflets and the whole branch is called 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.

What’s special about this post? I’ve tried to use ferns as examples for compound leaves as much as possible. I hope this would be a slightly different approach to learning about compound leaves and you will enjoy reading this!

Before actually getting into the topic, one should know what s simple leaf looks 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 leaflets attached to a stem through a petiole. The branch that contains the leaflets is 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,

Unipinnate

Single leaflets are present on the rachis in the opposite fashion.

Bipinnate

When the single leaflets of the unipinnate leaf get replaced with unipnnate leaves themselves become bipinnate leaves.

Tripinnate

When the single leaflets in the unipinnate leaves get replaced with bipinnate leaves, it is called as tripinnate leaves!

Quadripinnate

When the single leaflets in the unipinnate leaves get replaced with tripinnate leaves, it is called as quadripinnate leaves!

Decompound

These leaves do not have a pattern to count the number of times compound. The arrangement is compound but is not in a definite manner and can’t be classified under uni, bi, tri, or quadripinnate leaves.

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…

Unifoliate

These leaves contain a simple leaf blade with multiple lobes.

Bifoliate

These leaves will contain two leaf blades attached to the petiole at a single point.

Trifoliate

These appear to be three leaves originating from the anterior end of the petiole.

Quadrifoliate

Four leaves would be fused to a petiole and appear to be a single leaf.

Multifoliate

When more than four leaflets are attached to a petiole to form a single leaf, it is called a multifoliate palmately compound leaf.

Further Reading

Read about the genetics behind Compound Leaves in this interesting research article – https://dev.biologists.org/content/131/18/4401

Spines

In most xerophytes (plants that grow in regions of scarce water) like Opuntia, the leaves are reduced to spines and the stem is modified into storage parts that store water for the plants. They also become green and take the responsibility of the leaves by performing photosynthesis.

The spines will also be found in plants like Acacia that grow and survive well in drought conditions. The spines help reduce water loss. Also, they radiate the excess heat from the stems. They are also useful in absorbing droplets of water from the fog.

While in some plants like Ocotillo, the petiole gets elongated and the leaflets grow and the end of the petiole and as the plant matures, the leaflets fall off and the petiole remains as a spine.

Succulent leaves

Some plants like Aloe vera and many other succulents have managed to grow fleshy leaves that serve as a storage part for water as well as reserve materials. The plants can survive for months without even a single drop of water and may turn brown. But, even if it gets a little amount of water, the entire plant will turn green in days!

Tendrils

In climbers, the leaf of plants would be modified into elongated structures to help the plants climb efficiently. There are 4 types of tendrils as,

• Leaves may get modified into tendrils as in Pisum sativum where the apical leaves are modified into tendrils.
• In some plants like Tropaeolum majus, the petioles are elongated and they grasp the nearby plants for support.
• In plants like Gloriosa superba, The leaf tips get elongated and become tendrils.
• In some plants like Lathyrus aphaca, the entire leaf gets modified into a tendril and the stipules expand to carry out the function of a leaf.

Hooks

Some plants modify their terminal leaflets into hooks that help the climbers to hold onto its substrate. In Bignonia unguis-cati, the terminal leaflets turn into three hooks and help the plant to climb.

Swollen petioles

Aquatic plants live Eichhornia, have bulged petioles that are filled with air and help the plants to float on water.

 EichhorniaSalvinia natans

Leaves modified into roots

In Salvinia natans, an Aquatic fern, has three leaves that develop from each node. Two of the three leaves float above the water while the third leaf is submerged and is modified into a root.

Reproductive leaves

Plants like Bryophyllum daigremontianum produce adventitious buds along their leaf margins. These buds develop roots while on the parent plant and as they mature, they fall off the plant and start growing into a new plant when they land on nearby soil.

Sheathy leaf bases

Some plants lack true woody stems. For instance, Musa paradisiaca (Banana) plant the leaf base is expanded into a sheath that is rolled over one another in layers as new leaves grow. The sheathy leaf bases combine to form a pseudo stem that supports the plant to stand erect.

Traps

The plants that grow in nitrogen deficient places have modified themselves well to get it. The carnivorous plants like Nepenthes sp., the leaves are modified into a pod which is used to attract insects and other tiny animals to fall inside and digest them. The inner walls secrete digestive enzymes that help digest the insects and extract the nitrogen needed for the plant.

In Drosera burmannii, the leaf margins produce sticky substance that is irresistible to the insects and they fall for it. Then, the leaf rolls up to digest the insect.

In Utricularia vulgaris, the plant leaves are modified into bladders that capture small organisms and digest them. As something enters into the bladder, the valve closes and the digestion process begins.

Phyllode

In Acacia auriculiformis, the petioles expand to form Leaf like structures. They carry out the functions of the leaf. The true compound leaves appear in young plants and they fall off as they start growing. The true compound leaves may appear at the time of formation of seeds but they are short lived!