Leaves are classified into two main types, based on the arrangement of the leaf lamina, which is the site of photosynthesis and transpiration in plants. They are given below.
1. Simple Leaves
It is a single leaf with undivided leaflets that are directly attached to the stem. It is always attached to a twig by its stem or the petiole.
Examples: Maple, oaks, banana, guava, mango, black cherry, black gum and, sweat gum.
2. Compound Leaves
A leaf that is composed of multiple leaflets that are attached to the midvein, and have its stalk.
Examples: Neem, rose, clover, desert cotton, poison ivy, horse chestnut and, baobab.
Based on the types of leaf veins and their arrangement in the lamina, compound leaves are further classified into two types:
- Palmately compound leaves: They are leaflets radiating outwards from the end of the petiole, similar to fingers of the palm of our hands. Based on the number of leaflets, the palmately compound leaf is categorized into the following types: i) unifoliate – one leaflet, ii) bifoliate – two leaflets, iii) trifoliate – three leaflets, iv) quadrifoliate – four leaflets and, v) multifoliate – five or more leaflets. Examples: Citrus limon, Bauhinia yunnanensis, Acer cissifolium, Oxalis and, Umbrella plant.
- Pinnately compound leaves: They are leaflets arranged symmetrically along the center of the leaf, where each leaflet appears to be attached or pinned to the midrib making the leaf look like a feather. In a pinnately compound leaf, the midrib of the leaf is divided into numerous leaflets and all connected by a common axis. Eg., Neem. These can be further differentiated into:
- Tripinnate: Here, a tertiary axis bearing leaflets emerges from the secondary axis. Eg., Moringa
- Decompound: Leaf with more than three pinnate. Eg., old leaves of coriander
- Imparipinnate: Leaf with an odd terminal leaflet. Eg., Pea
- Pinnate: A compound leaf that has an axis on each side of the midrib is known as a pinnate leaf.
- Unipinnate: The leaf with leaflets on each side of the axis. Eg., cassia
- Bipinnate: Here, a secondary axis bearing the leaflet is produced by the central axis. Eg., Acacia