Modification of Leaves with Examples (Explained With Diagram)

In this article we will discuss about modification of leaves with examples (explained with diagram).

Many plants have modified their leaves so that they can perform functions other than photosynthesis and transpiration. These changes are sometimes made in response to environmental factors. Some of the important modifications are given below:

Modification of Leaves

1. Storage Leaves

Some xerophytic plants and members of the Crassulaceae family have thickened and succulent leaves with water storage tissue. Large parenchymatous cells with a large central vacuole filled with hydrophilic colloid characterise these leaves. This type of adaptation aids plants in conserving water and resisting desiccation (drying up).

2. Leaf Tendrils

In weak- stemmed plants, leaf or a part of leaf gets modified into green thread­like structures called tendrils which help in climbing around the support.

1) Entire Leaf is Modified, e.g., Lathyrus aphaca (wild pea) (Figure:1A), 2) Upper Leaflets Modified, e.g, Lathyrus odoratus (sweet pea) (Figure:1B), 3) Terminal leaflets Modified, e.g., Naravelia (Figure:1C).

Modification of Leaves with examples

Figure 2: A) lathyrus aphaca leaf is modified into tendril, B) pisum sativum upper leaflets modified into tendrils, C) naravelia terminal leaflets modified into tendrils, D) gloriosa leaf tip modified into tendril, E) clematis modified into tendril, F) smilax stipule modified into tendril.

4) Leaf Tip Modified into Tendril, e.g., Gloriosa (Glory lily) (Figure:1D), 5) Petiole Modified into Tendril, e.g., Clematis (Figure:1E), 6) Stipule Modified into Tendril, e.g., Smilax (Figure:1F).

3. Leaf-spines

Modification of Leaves with examples

Figure 3: Leaves spines of Opuntia, Figure 4: leaf-apex modified into spines, Figure 5: Argemone leaves modified into spines, Figure 6: barberry leaves modified into spines.

Certain plants leaves are completely or partially transformed into sharp, pointed structures known as spines for defensive purposes (Figure:3). Thus, in prickly pear, the axillary bud’s minute leaves are transformed into spines. The leaf-apex of date palm, dagger plant (Yucca) (Figure:4), and other plants is so modified, whereas spines develop on the margin as well as at the apex of plants such as prickly or Mexican poppy (Argemone) (Figure:5), American aloe (Agave), Indian aloe (Aloe), and others. The leaf of the barberry (Figure:6) becomes modified into a spine, whereas the leaves of the axillary bud remain normal.

4. Scale leaves

These are typically thin, dry, stalkless, membranous structures that are brownish or colourless. Their purpose is to protect the axillary bud that grows in their axil. When scale-leaves are thick and fleshy, such as in/onion, their function is to store water and food. Scale-leaves are found in parasites, saprophytes, underground stems, and other organisms. They can also be found in Casuarina, Asparagus, and other plants.

5. Leaflet Hooks

In Bignonia unguiscati the three terminal leaflets of leaf get modified into claw like hooks which help in climbing (Figure:7).

Modification of Leaves with examples

Figure 7: Bignonia Leaflet Hooks, Figure 8: Leaf Roots of Salvinia.

6. Leaf Roots

In case of Salvinia three leaves are present at one node. Out of these two leaves are normal and third gets modified into adventitious roots which help in floating over the surface of water (Figure:8).

7. Phyllode

In Australian Acacia (Figure:9), the petiole or any part of the rachis flattens or winges, taking on the shape of a leaf and turning green. The phyllode is a flattened or winged petiole or rachis. The normal pinnately compound leaf develops in the seedling stage, but it quickly falls off. The leaf’s functions are then carried out by the phyllode. However, in some species, young or even adult plants are seen to bear the normal compound leaves in addition to the phyllodes.

There are about 300 species of Australian Acacia (Acacia moniliformis), all showing the phyllodes. In lerusalem thorn (Parkinsonia; figure:10), a small prickly tree, the primary rachis of the bipinnate leaf ends in a sharp spine, while each secondary rachis is a phyllode being green and flattened. The leaflets are small and fall off soon. The phyllode then performs the functions of the leaflets.

Figure 9: Phyllode of Australian Acacia, Figure 10: Phyllode of Parkinsonia

8. Insect Catching

In insectivorous plants, the leaves are especially adapted to catch and digest insects to fulfil their nitrogen requirement. Some of the adaptations are given below.

(i) Leaf-Pitcher

This is an instrument for catching insects in order to replenish the nitrogen deficiency in the medium in which the plant is growing. In the case of Nepenthes, Dischidia, and Sarracenia, the leaf-lamina is transformed into a pitcher-like structure known as a leaf-pitcher (Figure:11).

Nepenthes, also called pitcher-plant bears special type of leaves. Leaf-base is winged, petiole is tendrillar and lamina is modified into pitcher-like structure having a coloured lid which attracts the insects and keeps the pitchei closed during immaturity. The rim of the pitcher is internally lined by backwardly directed hair and a large number of minute scales due to which the insect slips and is captured.

The inner walls of the pitcher have glands which secrete a digestive fluid into the cavity of the pitcher. The insect is digested here and waste material settles down at the bottom. Sarracenia has pitchers in the from of rosetts. The pitchers are similar to those of Nepenthes but are sessile. 

Pitchers are also found in Dischidia, an epiphytic climber. Rain water and debris accumulate inside the pitchers. The roots from the nodes of the stem grow into the cavity of the pitcher and absorb water.

Figure 11: Nepenthes leaf-pitcher, Figure 12: Utricularia leaf bladder, Figure 13: Insectivores plant of drosera.

(ii) Leaf Bladder

Utricularia is another insectivorous plant which grows in water. It bears highly dissected submerged leaves. Some of the segments of the leaf are modified into bladders or utricles (Figure:12).

The inner wall of the bladder is lined by digestive glands. The opening of the bladder is provided with a valve which opens inwards. On the valve and rim of the opening are present long and branched bristles. Minute water animals get entangled in the bristles, valve opens inwards and animals go in and valve gets closed. These are digested inside the vessel.

(iii) In Drosera

The lamina is covered in spine-like hairs that spread outward. At the tip of each hair is a gleaming sticky globule containing digestive enzymes. These hair is extremely sensitive to touch (Figure:13). When an insect lands on the lamina, the hairs bend and completely cover it, leaving no way for the insect to escape. The poor insect is digested by enzymes found in the shining tips of hairs. After the insect has been digested, the hairs return to their original position.