A compound leaf is a type of leaf where the leaf blade is divided into two or more smaller, independent units called leaflets. The two main types of compound leaves are pinnately compound and palmately compound.
Here's a more detailed explanation:
Compound Leaf Definition
Unlike a simple leaf, which has a single, undivided blade, a compound leaf's blade is separated into multiple leaflets. These leaflets are attached to a central stalk (rachis), which is an extension of the petiole (leaf stalk). It is crucial to distinguish leaflets from simple leaves; the presence of a bud at the base of the petiole (where it attaches to the stem) identifies it as a leaf rather than a leaflet.
Types of Compound Leaves
There are two primary classifications of compound leaves, distinguished by the arrangement of their leaflets:
-
Pinnately Compound Leaf:
- In a pinnately compound leaf, leaflets are arranged in rows along both sides of an extended petiole called the rachis. Think of it like a feather (pinna means "feather").
- Examples: Rose leaves, ash trees, walnut trees.
- Pinnately compound leaves can be further subdivided:
- Odd-pinnate: Having a terminal leaflet at the end of the rachis (e.g., rose).
- Even-pinnate: Lacking a terminal leaflet; instead, the rachis ends with a pair of leaflets (e.g., locust tree).
- Bipinnately compound: The leaflets are further divided into smaller leaflets (e.g., Mimosa).
-
Palmately Compound Leaf:
- In a palmately compound leaf, all the leaflets radiate from a single point at the distal end of the petiole, resembling the palm of a hand with fingers extending outwards.
- Examples: Horse chestnut, Virginia creeper.
| Feature | Pinnately Compound Leaf | Palmately Compound Leaf |
|---|---|---|
| Leaflet Arrangement | Leaflets arranged along both sides of the rachis | Leaflets radiate from a single point |
| Resemblance | Resembles a feather | Resembles a palm of a hand |
| Examples | Rose, Ash, Walnut | Horse Chestnut, Virginia Creeper |
In summary, a compound leaf has a divided blade forming leaflets, distinguished by the arrangement of these leaflets as either pinnately compound (feather-like) or palmately compound (hand-like).
