Leaves are an essential part of plants. They photosynthesise and produce food for plants. Leaves are mainly of two types, simple and compound leaves. Compound leaves are further classified into two types, mainly pinnately and palmate compound leaves. When we surround ourselves with nature, we are mesmerised by the bright green colour which strikes our eyes. This green colour comes from leaves. Leaves are born on the stem and rise at nodes. Have you ever thought about where the green colours on leaves come from?
Chlorophylls absorb light which allows plants to collect energy from the Sun. As a result, leaves are green because chlorophylls absorb every colour of UV light except for the green colour. When you look closer at leaves have you ever noticed how different they are in shape, size, and texture? There exists a wide diversity between leaves. There are some general characteristics between them but some have unique abilities.
Leaves are built from three main types: the base, the blade, and the petiole. The longest part of the leaf is the blade. The base is known as the region of the blade that attaches to the petiole.
Simple Leaves – Simple leaves possess the entire lamina. Even if the lamina is carved, it does not reach the midrib. They do not have leaflets.
Compound Leaves – Compound leaves possess leaflets. The lamina of a leaf is divided into many leaflets and blades.
A leaf that can not be further divided into any smaller sections or leaflets is called a simple leaf. This type of leaf joins the stem through the petiole.
Simple leaves consist of four parts:
Leaf Base - It is the expanded area where the stem and leaf connect.
Stipules - The position of the stipule changes depending on the species of the plant. These small bud-like structures are situated near the leaf base.
Petiole - The petiole is the part that adheres the leaves to the stems. Plants can have short, long, or no petioles at all.
Lamina or Leaf Blade - The green extended part of a leaf is called the lamina or leaf blade. This part consists of mesophyll that helps in performing photosynthesis.
Compound leaves are those leaves when the lamina of a leaf is divided into many leaflets. The incision made in the lamina is reached into the midrib which is further divided into multiple leaflets. The leaflets in the compound leaf do not possess buds in their axes.
Compound leaves are of two types:
Pinnate Compound Leaves
Palmate compound leaves
In pinnate compound leaves, leaflets are present on the common axis. The midrib is represented by the common axis called the rachis.
Examples: Ash, Hickory, Walnut, Pecan, Black lotus, Neem, Cassia fistula.
There exist three types of pinnate leaf arrangement:
Even-pinnate Leaflet Arrangement: In this arrangement, leaflets are in pairs along the rachis without a single terminal leaflet. This type of arrangement is also known as paripinnate.
Odd-pinnate Leaflet Arrangement: In this arrangement, instead of a terminal pair of leaflets, there is a single terminal leaflet at the top. This type of arrangement is also known as imparipinnate.
Alternate-pinnately Leaflet Arrangement: In this type of arrangement, leaflets are produced alternately along the rachis with a single terminal leaflet. This type of arrangement is also known as aternipinnada.
Pinnate Compound Leaves and Types
Pinnately leaves that further divide are called bipinnately compound leaves. These compound leaves have leaflets from secondary rachises. The axillary buds are actually found in the angle between the petiole and the stem of pinnate leaves, not in the axils of leaflets is the main distinguishing factor to recognize bipinnate leaves.
Even if these leaflets are twice or thrice divided, they all still account for one leaf branching off the stem. Since the leaflets are formed on primary and secondary veins, the leaflets formed are given the name pinna.
In simple palmate leaf, the leaflets are formed and arise from a single point of attachment called the distal end of the rachis.
Each leaf is a part of an individual leaf and all are branching from the axil part of the leaf. These compound leaves do not have rachises as each palmate branches out directly from the petiole, each petiole may also branch off to other petioles.
Examples: Clover, potentilla indica, oxalis, Silk, and Cotton.
Leaf cells consist of organelles known as chloroplasts which contain specialised pigments called chlorophyll.
Since leaves do not absorb green colour, they instead reflect it which is seen by our eyes.
What are the two types of compound leaves?
Ans: The two types of compound leaves are pinnately and palmately compound leaves. In pinnately compound leaves, leaflets are present on the common axis and in palmately compound leaves, leaflets are present on the distal end of the rachis.
What are the various parts of the leaves?
Ans: The various parts of the leaves are midribs, axil, stem, leaf base, petioles, vein, venules, tip, and leaf base. Each part of the leaf has a function that is used in the function of the leaves.
Just like the name of the palmately compound leaves, the whole leaf is shaped like the palm and fingers of your hand.
Pinnately leaves show the resemblance of a feather.
1. How do you identify different types of leaves based on their appearance?
If there is only one blade on the stalk, then it is a simple leaf, but if there are many blades on the stalk, then it is a compound leaf.
2. What does the term venation mean in a leaf?
The term venation is used to describe the arrangement of the veins in a leaf lamina. There are two types of venation. The first is Reticulate venation which means the veins form a network and the other is parallel venation which means the veins run parallel to the midrib each other.
3. Give examples for simple and compound leaves?
Examples of simple leaves are blackberry, banana, mango, oak, maple, etc. Examples of compound leaves are pea, mimosa, rose, clover, shame plant, etc.