Plants can often be identified based on their leaves. Although it is not always possible to determine the exact species, it may be surprisingly easy to use leaf characteristics in order to figure out what family you are dealing with. What follows is a list and description of some of the most common methods of leaf-based plant identification.
Leaves can be divided into two basic categories: simple and compound. Simple leaves are those that grow separately from one another. Some leaves, on the other hand, are divided into many separate parts, or leaflets. While some compound leaves can consist of only a few leaflets, others have many. These can be arranged in any number of different ways.
Although leaf type is an important means of identification, it is usually a good idea to take several factors into account before determining what plant you're looking at. Keep in mind that plants from entirely different families may have identical leaf types.
Leaf type is only a useful method of identification when combined with leaf arrangement. There are three basic leaf arrangements. Opposite leaves grow exactly opposite each other on the stalk, alternate leaves grow at different intervals on either side of the stalk or branch, and a whorled arrangement means that several leaves come out of the stalk at the same place.
When discussing leaf characteristics, botanists usually refer to both type and arrangement. For example, a mimosa bush has compound alternate leaves, while jacaranda trees have compound opposite leaves.
There are many different types of leaf margins that can be helpful in distinguishing different species of plants. Some of the most common types are entire (with smooth margins), lobed (herbs such as cilantro have lobed leaves), serrate (saw-like edges) and dentate (indentations resembling sharp teeth).
While many plants can't be identified based on the colour of their leaves, some have wild colouration and distinctive markings or patterns that make them easy to recognise. In certain cases, the colour of the underside of the leaf can be just helpful as that of the leaf surface in helping to determine the species.
The leaves, bark or flowers of some plants may have a very particular odour. Some common examples are plants that belong to the eucalyptus, mango, citrus and avocado families. Odours, however, can be deceptive, so it is best to check for other characteristics such as leaf arrangement, shape and type before making a positive identification.
In some instances, a plant can be identified easily based solely on the shape of its leaves. One famous example is the Swiss cheese plant (Monstera deliciosa), whose mature leaves develop holes that allow light to filter down to its base.