It is a no-brainer that leaves are one of the most important parts of a tree. In fact, most the trunk and the branch exists to support the leaves. The very main purpose of a tree is to grow high enough so that it can catch the sunlight.
Leaves help in photosynthesis, which keeps the tree alive. They have their unique shape, unique margin, venation, colour, and arrangement on the branch. Since we are on the subject of leaves, let’s look into its types and functions.
Functions Of A Leaf
Leaves performs various functions which include making food, interchange of gases between the atmosphere, the plant body and evaporation of water.
Structure of a leaf
Before getting into the details and all the technical jargon related to leaves and their parts, we must understand the structure of a leaf. Leaves are the kitchen of the plant. A leaf can broadly be divided into two parts: the leaf blade and the petiole.
The leaf blade, also called the lamina is broad and flat. This is where photosynthesis occurs. There is a midrib that goes all the way in the middle through which other branches arise. These are called veins.
Veins can be of different types depending on the number of blades and pattern of veins. The petiole is a stalk-like structure that connects the leaf to the branch. It is composed of tiny tubes that connect the veins to the stem. They also enable water transport to the leaf from the roots.
Some plants may also have stipules, flap-like structures that grow at the base of the petiole. It is helpful in tree leaf identification.
What is Venation?
As mentioned earlier, the pattern of veins is different for different kinds of leaves. This arrangement is called venation. Venation can be of three types: parallel, pinnate, and palmate. Parallel venation occurs when veins are arranged parallel to each other.
These veins are smaller and run lengthwise on the leaf. Pinnately veined leaves are composed of the main vein in the middle of the leaf with small branches of veins, just like a feather.
Palmately-veined leaves have many principal veins that branch out from the main midrib. You will have to take a close look at the leaves if you wish to identify the leaf from veins.
Tree leaf identification: Shapes
The shape of the leaf can also help in tree leaf identification, especially when it comes to broadleaf. Some common leaf shapes are lanceolate (long and narrow), triangular (also, deltoid), ovate (egg-shaped, round, and cordate (heart-shaped). Two shapes are popular and can be easily identified – the palm-shaped maple leaf and lobed oak leaf.
Types of Leaf Arrangement
Known as phyllotaxy in botanical language, leaf arrangement on the stem can be an indicator of the tree. It is also a method for tree leaf identification.
The most common categories of leaf arrangement are simple and compound leaves.
A simple leaf is called simple because it is the simplest form of a leaf. The leaf is joined to the stem through the petiole without any subdivisions. It is directly attached to the tree bud. Some common plants exhibiting simple leaves are – Oregano, Maples, and Hibiscus. Its blade is completely undivided.
A Simple Leaf Has Four Parts: A leaf base where the leaf attaches to the stem, Stipules which are located near the base of the leaf, petiole that attaches the leaf to the stem, and lamina which is a thin, green part that performs photosynthesis.
In a compound leaf, the leaf blade is divided forming many leaves. Common examples of compound leaves are Rose and Neem leaves. A compound leaf has many leaflets joined to the stem through a petiole. The stem on which this kind of arrangement is seen is called the rachis, which is a modified mid-vein. Compound leaves can be further classified into:
Pinnately Compound Leaves: ‘Pinnation’ means the subdivision of a leaf into leaflets. This leaflet arrangement can further be classified into three types – Unipinnate, Bipinnate, and Tripinnate. When there is a regular arrangement of leaflets on the rachis, it is called uni-pinnate. In bi-pinnate arrangement, there is a secondary rachis on which leaves are arranged. Similarly, a tripinnate arrangement has three stems.
Pinnately compound leaves can also have an odd-pinnate leaflet arrangement or an even-pinnate leaflet arrangement. Tamarind has an even-pinnate arrangement where the arrangement of the leaflet is oppositely, and the termination points are sprout with two leaflets. Acacia has an odd-pinnate leaflet arrangement where the rachis at the end is sprouted with a single leaflet.
Palmately Compound Leaves: When leaflets arise from a common point of the petiole, it is called palmately compound leaf arrangement. These leaves are compared with the fingers of the palm, hence the name. The arrangement can further be divided into unifoliate, bifoliate, trifoliate, and quadrifoliate depending on the foliage.
Leaves can be arranged in different patterns. Some of them are:
Opposite Leaf Arrangement
On trees and shrubs with opposite leaf arrangements, leaves arise from the same node on the opposite side of the stem. The leaf arrangement can further be divided into two types – decussate and distichous. Decussate is an arrangement where each succeeding pair of leaves is at right angles to the pairs above and below them. It can be found in the mint family, the maple family, and some members of the milkweed family.
The opposite of decussate is distichous. This is when the pairs are not rotated. When you look at the pictures of opposite leaves, you will find that the leaves are in pairs on either side of the stem. The leaf shape depends on the species of the tree.
Whorled Leaf Arrangement
When three or more leaves are attached to a single node, it is called a whorled leaf arrangement. This arrangement is called a verticillate arrangement. They grow in a similar manner as opposite leaves. However, instead of just two leaves in an opposite pair, there are at least three leaves. This arrangement can be seen in catalpa. Some other examples of shrubs with whorled leaf arrangement are lemonwood, blackboard tree, Japanese clethra and mountain laurel.
This is an arrangement where leaves arise from the base of a plant. After the older foliage starts looking weak and tired, the leaves are trimmed to get new foliage. You will find this arrangement mostly in perennial plants like pulmonaria.
Rosettes are dense, radiating clusters. They form at the base of the plant. They occur in common dandelions, sunflowers, and aster families. Some biennial plants like carrots produce rosettes during the initial years of growth and transform into a stem with alternate leaves later.
A similar arrangement is a distichous arrangement where leaves are arranged in two rows on opposite sides of the stem. This is also called a two-ranked leaf arrangement.
Classification based on Shapes of The Edges
Unlobed or entire leaves are usually oval or round-shaped. This type of leaf does not have any special features.
This type of leaf is composed of earlobe-like shapes and is easy to identify. The shapes may differ from species to species. The indentations between the lobes can be either deep or shallow. This space is also called the sinus. Have you seen oak trees? They have lobed leaves. You must have seen pointed as well as rounded lobes.
As the name suggests, leaves with tooth-like shapes in the edges are called toothed leaves. These shapes can also be extremely fine and not visible properly through the naked eye. These leaves are physically beautiful and may look like a steak knife. Some leaves have softer edges. Examples are chestnuts, hazel trees, and ash trees.
Coniferous Tree Leaves
Coniferous tree leaf identification is easy as the leaves are needle-like, which can be soft or hard. Coniferous evergreen trees like spruce, cedar, and fir trees have this type of leaves. The shape is due to the need to maximize photosynthesis in cold and dry conditions where water is scarce.
Conifer class, also called Pinopsida, has needle-like leaves that are aromatic. This is where many needles are attached to the branch or twig.
Cluster and Bundle Needles
The leaves grow in bundles of evergreen needles along with the twigs of the tree. This tree leaf identification method can be used to differentiate between pine trees and fir trees because pines have cluster needles while firs have single needles.
Tree Leaf Identification: Margins or Edges
The overall shape and pattern of leaves are greatly determined by the margin and edges. This is true, especially with lobed leaves. Various terms to define different leaf margins are crenate, dentate, serrated, and undulated. Some of them have toothed edges while some have round ones. Some have a combination of both.
Tree Leaf Identification: Some Common Types of Leaves
The image of a leaf in our head is the same: a green-colored flat structure with a small stem-like part at one end. We also know that they change colors with season and time. However, leaves are not just that. There are many kinds of leaves and tree leaf identification will become easy when you know them.
Angiosperms (Flowering Plants) Leaves
This one is the normal, classic leaf with a skeleton of leaves and membrane within them. Most shrubs and deciduous trees have such leaves. Leaves of flowering plants are very efficient when it comes to the basic task that must be performed by them. They have a large surface area, so they are great at catching sunlight for photosynthesis.
Each plant has a different kind of leaf arrangement depending on the species. Leaves adapt themselves in such a way that they do not throw shade at each other. Leaves can also start growing from the stem itself. They can be arranged in rosette, opposite, whorled or literally any kind of arrangement. The varieties are endless.
There is a disadvantage for these leaves as well. They attract animals, especially insects. That is the reason why they shed themselves every year so that fresh and new leaves can start growing.
A frond is a single leaf that is divided into smaller segments. You must have seen such leaves in ferns and palms. Each leaf grows out from a single stalk in a series of separate blades. The leaves often have complex shapes but the whole front is just a single leaf. Pests and diseases affect the appearance of these plants drastically.
Grasses are a class of plants. These species are loved by gardeners. Grasses also include exotic plants like bamboo as well as normal grass on your lawn. Grasses are of different types but most of them have the same form of leaf – long, slim leaves that grow from the base of the stem. They can have a single leaf or many leaves, depending on the species.
Some plants have very unusual, special leaves for specific purposes. Tree leaf identification is easy as the leaves are unique, and only one variety of plants own them. For example, the leaves of pitcher plants are like containers with a ‘mouth’ to trap insects. These leaves perform the same functions as normal leaves, like photosynthesis, collecting carbon dioxide, and releasing oxygen. But they also perform special functions such as sensing the arrival of an insect.
Tree Leaf Identification of Common Plants/Trees
Mulberry trees have delicious blueberries. But do you know you can easily identify them with the help of their leaves? They have simple leaves with toothed edges and an irregular pattern of lobes. Since they are deciduous, they have leaves that are branched alternatively. Most leaves have a fuzzy texture.
They are one of the most popular tree families in the world. You must have seen the leaves. White oaks have a round leaf with acorns. Black oaks have bristles on the leaves (and extremely bitter acorns). All oak trees have lobed leaves which can either be rounded or pointed.
These are probably the most easily recognizable coniferous trees in the world. They have clusters of green needles, that are mostly concentrated towards the top. They also produce hard cones called pinecones.
These are our common Christmas trees. They have a dense needle leaf distribution which makes them look denser and greener. As compared to other coniferous trees, fir needles are soft and flat with two white stripes at the bottom of each leaf.
Fir tree leaves can also change color and become purple, blue, or golden as they mature. A distinguishing feature to identify a fir tree is that the leaves grow upwards while others tend to grow downwards.
Elm trees can be identified with leaves, easily. The leaves they own are classified as broadleaf. The leaves have the same pointed oval shape; however, this may vary according to the elm tree species. The leaves can range from 7 to 16 cm long.
Tulip trees are aesthetically pleasing. The leaves are rectangular, with 4 to 6 lobes and up to 15 cm in length. These trees tend to bloom before the leaves grow, which means that the large leaves cover the blooming flowers. You can easily identify a tulip tree from its leaves and orange-yellow flowers.
Tree leaf identification of cedar trees is comparatively easier. They are one of the few species with scale leaves. They grow in spiral clusters. The foliage can either be dark green or blue.
Cottonwoods can be identified through triangular or circular leaves with a long leaf stalk. The genus has alternate branches and a cottony seed.
Hickory trees have long and narrow leaves. The leaves are composed of clusters of leaflets. The
leaflets grow on opposite sides of the stem.
The leaves are oval-shaped with pointed leaves. The terminal leaf is usually the largest in size. You will always find several leaflets in a
Tree Leaf Identification: Leaf Modification
Apart from photosynthesis, leaves have many other functions that they perform like support, defense, storage of food, etc. To perform these functions, leaves modify themselves in different forms. Knowing these forms is necessary for better tree leaf identification.
Plants that require their leaves to store water have thick and succulent leaves. The cells of these leaves are filled with hydrophilic colloids.
Have you seen a pea plant? It has tendrils as the stems are weak. These tendrils are modified leaves to support the plant. Tendrils wrap around nearby sticks or walls to support the plant.
Leaf Hooks and Roots
Terminal leaves in some plants get modified into hook-like structures that help them in climbing. Leaf roots are present in aquatic plants, where they help them to float in water by getting modified into adventitious roots.