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It has been ascertained now that the plant size, rate of leaf production, internal length, thickness, shape and area of leaves and their orientation to light and the period if their exposure is important, can factor in determining crop productivity.
The presence of leaves of more than one shape is termed heterophylly which is mostly seen in amphibious plants. The finely dissected leaves are adapted to the sunken conditions whereas the entire leaves are aerial.
Example – Limnophila
What is Phyllotaxy?
The arrangement of leaves on the stem and on the branches is called phyllotaxy. The purpose of the arrangement of leaves in a particular manner is to prevent overcrowding and to expose the leaves in such a way that they are exposed to the most beneficial position towards the light for the process of photosynthesis.
Types of Phyllotaxy
The following three kinds of leaf arrangements are found under phyllotaxy –
Alternate phyllotaxy
When a single leaf arises at each node is called Alternate phyllotaxy. It is also called Spiral phyllotaxy.
Alternate Phyllotaxy Examples – Mango, Mustard, China rose, etc
Opposite phyllotaxy
When two leaves are present at each node and standing opposite to each other is called opposite phyllotaxy. There are two kinds found:
Opposite decussate
One pair of leaves is placed at a right angle to the next upper or lower pair of leaves, which is known as the opposite decussate.
Examples – Ocimum and Calotropis
Opposite superposed –
The paired leaves at consecutive nodes are in the same direction which means two opposite leaves at a node lie exactly above those at the lower node, which is known as opposite superposed.
Examples – Jamun and Rangoon creeper
Whorled phyllotaxy
When more than two leaves are present in a whorl at each node is called whorled phyllotaxy.
Example – Oleander, Alstonia
The difference between Phylloclade and Phyllode
Phylloclade | Phyllode |
Phylloclade is a modified stem | phyllode is a petiole that has been modified into a lamina-like structure. |
Phylloclade arises in the axil of the caducous leaf from the node | In the case of phyllodes it does not arise in the axil of the leaf |
Phylloclades does not bear axillary buds | phylloclades bear axillary buds. |
Phylloclades may bear bristles, scale leaves and flowers | phyllodes have no such structures borne on it. |
phylloclades due to storage of water and food it may be thick, fresh and succulent | phyllodes does not store food and water and is never succulent. |
Example of phylloclade – Opuntia | Example of phyllode – Acacia |
Functions of the leaf
The main function or purpose of the leaf is as given below:
- Leaves store water to resist roughness as in Aloe and Agave. In onions, food is stored in the leaf bases.
- Various leaf parts such as lamina, petiole, stipules, etc, get modified into tendrils to help the weak plants climb in search of light and air.
- Leaves are modified into sounds to provide protection from browsing animals and to reduce water losses through transpiration. Example – Berberis
Bud-scales protect the growing point. Example – Ficus
- In plants, leaves are brightly coloured to attract insects for pollination.
- The floral leaves are modified into sepals, petals, stamens and carpets to carry out reproduction.
- Plants like Nepenthes and Utricularia, the leaves are modified into insect traps to capture the insects. By digesting the insect proteins, leaves fulfil the nitrogen deficiency.
- In xerophytic plants, succulent leaves store water, mucilage or latex to protect the plant from its destination.
- Leaves are modified into hygroscopic appendages to absorb moisture from the atmosphere.
Example – Tamarix
- Leaves bear adventitious buds and help in vegetative propagation.
Example – Bryophyllum, Begonia
- The petiole stores air and provides buoyancy and the plant can float.
Example – Eichhornia, Trapa, Nelumbo
Importance of studying Leaf
The question why we need to study leaf and its part is because it holds an importance in our day to day life. Few points given below :
- It is possible to tell the physiological maturity of a plant by the shape of its leaves. Example – Cotton plant and Eucalyptus.
- Foliage plants form an important item of the horticulture industry. Several plants have been assigned with leaves in various shoes, sizes and colours for their ornamental values.
- The leaves of certain plants are of economic value.
Example – Thea Sinensis (Tea)
Conclusion
Hence, in botany, phyllotaxis or phyllotaxy is the arrangement of leaves on a plant stem. Phyllotactic spirals form a distinctive class of patterns in nature.The motive of the arrangement of leaves in a particular manner is to prevent overcrowding and to expose the leaves in such a way that they are exposed to the most beneficial position towards the light for photosynthesis.
