Basically, leaves are categorized into simple and compound forms. This article will provide you with information about compound leaf identification.
We all know that in most of the plants and trees, leaves are responsible for carrying out photosynthesis. It is this process that helps the plants to make their food. Apart from that, leaves can also store food and water. In some plants, leaves are modified for these purposes. There are thousands of different plants and trees in the world and most of them have leaves of different, shapes, sizes and colors. Even their arrangement on the stem may vary from one tree/plant to another. Distinguishing the leaf types is one of the key factors that will help in identifying specific trees.
Simple and Compound Leaves
So, it is a common fact that leaves may not be similar for all plants and trees. They may have different shapes, sizes, patterns and arrangements. A leaf has a lamina or leaf blade, which is the main broad part of the leaf, which is attached to the petiole, which in turn joins the stem. The location where the petiole joins the stem is called the leaf axil, which sports two small bud-like structures called stipules. This is only a generic description of a typical leaf, but some leaves may not be broad, whereas some may not have petioles or stipules.
Basically, leaves are classified into simple and compound types. As the names rightly suggest, simple leaves are those leaves in which the leaf blade or lamina is undivided. For example, the leaf of a hibiscus plant has a leaf blade with no lobes or division. Most of the pear plants, basil, oregano and rubber plant are found to have simple leaves. However, some of the simple leaves have lobes (the leaf blade will be divided), but the gaps between the lobes do not reach the mid vein of the leaf. For example, a sassafras tree leaf has three lobes, but is a single leaf (as shown in the first image below). In such cases, the division of the leaf blade creates three lobes, but not three leaflets. Other examples for such simple leaves with lobes include most of the maples, sycamore, black oak and scarlet oak. The following images are that of some simple leaves.
Now you know that the leaf blade of a simple leaf is undivided. But, some of the simple leaves have partial division of leaf blades, forming lobes and not distinct leaflets. If you find a leaf with complete division of leaf blade, then it is a compound leaf. One such example is rose plant. In this case, the leaf is divided completely along the mid vein, to form leaflets. Each of these leaflets may appear like a simple leaf. The stem on which the leaflets are arranged is called a rachis (modified middle vein). There are different types of compound leaves, which are categorized into different forms.
Compound Leaf Types
A simple form is trifoliate or trifoliolate type. It can be inferred from the name that these compound leaves have three leaflets only. For example, leaves of common beans, strawberry, soy beans, white clover and laburnum, are found to have trifoliate leaves.
A leaf in which the leaflets are arranged in pairs, along the mid vein or rachis is called a pinnately compound leaf. If there is no terminal leaflet, then it is even pinnate (mahogany, candle bush and tamarind) and if there is a terminal leaflet, then it is an odd pinnate leaf (like some acacia, mockernut hickory, pecans and roses).
In some plants like flame trees (otherwise known as royal poinciana or flamboyant), bird of paradise tree and silk trees (Albizia), you may find a rachis, along which compound leaves are arranged. In other words, the rachis has secondary stems on which the leaves are arranged. These leaves are called bipinnately compound leaves.
A palmately compound leaf has leaflets radiating from a single point – tip of the petiole. As the arrangement of these leaflets are compared to fingers on the palm, such leaves are termed as palmate leaves. Buckeye, horse chestnut, desert cotton, cassava, and hemp plants have palmately compound leaves.
In some plants, the pinnate division of leaf blade is almost complete, but the leaflets are not fully separate. In other words, the leaf blade will be divided till the mid vein only. This type of compound leaves are known as pinnatifid, as seen in certain types of ferns, belonging to the genus Polypodium, some types of philodendrons, arugula, corn sow thistle and some plants in the genus Sorbus.
The above said is only a brief overview about compound leaf identification. These types may be further classified on the basis of their design and mode of arrangement on the stem. If you are interested in knowing more about compound leaves, you may conduct a detailed study about them. A basic understanding about the features of a tree will help you in identifying that tree. Leaves are one of the main parts of trees and if you can understand the type of the leaves in a specific tree, it will prove beneficial in identifying that tree. So, if you are a tree enthusiast, it is always better to enhance your knowledge about tree leaves.