Sometimes plant parts can evolve and take on new functions. Many plants have a part called a petiole that attaches the leaf to the stem. On some plants, the petiole has changed because of environmental reasons so that it looks just like a leaf and is called a phyllode. It develops the ability to photosynthesize and function as foliage.
Main stems like branches and flower stalks (known as rachis) can also become phyllodes.
Phyllodes are found on most species of acacia trees and shrubs. Many of them start out with true leaves as seedlings, but they fall off after the phyllodes have developed. The Mexican palo verde (Parkinsonia aculeata) also has phyllodes.
Petioles and Phyllodes
In flowering plants, a petiole is generally slender and chiefly renders support by attaching the leaf blade to the stem. In some plants, the petioles become modified or specialized in a way that they become leaf-like in appearance (expanded) and serve not only to support the leaf but to carry out photosynthesis as well. The phyllodes of Acacia koa for instance, are thick and coriaceous helping the plant in surviving stressful environment.
In mosses, the phyllodes refer to the leaf-like structures of the moss plant in the gametophyte stage. The phyllodes are not regarded as true leaves although similar in appearance and function. It is because phyllodes do not have vascular tissues.
Phyllodes and Phylloclades
The main difference between phyllode and phylloclade is, a phyllode is a modified petiole or a shoot that connects the stem with leaf. It resembles the function of leaf. While phylloclade is a modified stem, that is responsible for photosynthesis. It also acts like a leaf.
Key differences include:
- Phyllode is a modified leaf, a petiole, while phylloclade is a modified stem.
- In Phyllode petiole is changed to a planed, leaf like structure green in colour showing photosynthesis while in phylloclade stem is reformed into flat, green leafy structure to photosynthesize.
- Phyllode bears an axillary bud while phylloclade does not.
- Phyllode flower or bud are absent while in phylloclade it is present.
- Phyllode does not branch while phylloclade does.
- In Phyllode spines are absent and in phylloclade it is present as axillary buds.
- Scaly leaves are absent in Phyllode while it is present in phylloclade.
- In Phyllode node and internodes are absent while are present in phylloclade.
- Example of Phyllode is Melanoxylone and Acacia while phylloclade is Cactus and Cocoloba.
Phylloclades and Cladodes
A similar adaptation of a stem is called a cladode. Here are the differences:
- It is an aerial stem or branch modification.
- Here the stem is modified into a flat or cylindrical, succulent and green structure.
- It arises in the axil of the leaf which falls off, leaving a scar.
- It bears succession of nodes and internodes at long or short intervals.
Example: Opuntia, Casuarina.
- It is an aerial branch modification.
- Here the branch is also modified into a succulent, green, flat or cylindrical or leaf-like structure.
- May appear in cluster or singly in the axil of scale leaf.
- It is a phylloclade of mostly one or rarely two internodes only.
Example: Asparagus, Ruscus.