Leaf Adaptations
Across the three plant groups, adaptations of their leaves are extremely varied, due to the great differences of their ecological niches.
Due to the unique niche of hydrophytes, the abundance of water means that these plants must manage an excess supply of water. Leaf adaptations vary for different hydrophytes, due to the differences in their ecological niches.
Hydrophytes that are fully submerged generally do not have a cuticle or stomata. The waxy cuticle found on mesophytes is absent in underwater hydrophytes, since water loss is not a limitation for these plants, in contrast, transpiration is required to ensure that the limitation of having excess amounts of water is prevented. Unlike mesophytes, the ecological niche of hydrophytes means that water, minerals, and any other essential resources, enter the plant by direct diffusion of the surrounding water moving into the plant. This means that submerged hydrophytes typically have no need for stomata.
Hydrophytes that are fully submerged, such as Elodea, have also adapted to grow thin, ribbon-like leaves that are highly divided [15]. This increases the surface area for diffusion of water and dissolved minerals into the plant. In doing so, this allows for the plant to gain resources more efficiently, primarily so that photosynthesis can be carried out, allowing the plants to carry out life processes and survive.
Hydrophytes with floating leaves have stomata only on the upper side of the leaf, unlike mesophytes which have stomata concentrated on the bottom [6]. The stomata are found on the upper epidermis to allow efficient gas exchange with the air. Efficient gas exchange of carbon dioxide in and oxygen out will enable the plant to carry out photosynthesis, which consequentially allows the plant to carry out life processes such as respiration, growth and reproduction. This essentially allows the plant to survive and live successfully.
Due to the unique niche of hydrophytes, the abundance of water means that these plants must manage an excess supply of water. Leaf adaptations vary for different hydrophytes, due to the differences in their ecological niches.
Hydrophytes that are fully submerged generally do not have a cuticle or stomata. The waxy cuticle found on mesophytes is absent in underwater hydrophytes, since water loss is not a limitation for these plants, in contrast, transpiration is required to ensure that the limitation of having excess amounts of water is prevented. Unlike mesophytes, the ecological niche of hydrophytes means that water, minerals, and any other essential resources, enter the plant by direct diffusion of the surrounding water moving into the plant. This means that submerged hydrophytes typically have no need for stomata.
Hydrophytes that are fully submerged, such as Elodea, have also adapted to grow thin, ribbon-like leaves that are highly divided [15]. This increases the surface area for diffusion of water and dissolved minerals into the plant. In doing so, this allows for the plant to gain resources more efficiently, primarily so that photosynthesis can be carried out, allowing the plants to carry out life processes and survive.
Hydrophytes with floating leaves have stomata only on the upper side of the leaf, unlike mesophytes which have stomata concentrated on the bottom [6]. The stomata are found on the upper epidermis to allow efficient gas exchange with the air. Efficient gas exchange of carbon dioxide in and oxygen out will enable the plant to carry out photosynthesis, which consequentially allows the plant to carry out life processes such as respiration, growth and reproduction. This essentially allows the plant to survive and live successfully.
The leaves of hydrophytes which float on the surface of the water, such as Nymphaeaceae plants (water lilies), are typically thin but very large is diameter [8]. Having large leaves maximizes the surface area for water evaporation, in order for transpiration to occur quickly. This is required so hydrophytes do not receive too much water.
In mesophytes, the leaves on the majority of plants are relatively large in size. Since they are found in temperate conditions with sufficient water available, mesophytes can produce big leaves to maximize the surface area for light absorption, which is crucial for photosynthesis to occur, and the survival of the plant. The leaves of some mesophytes also consist of a waxy cuticle. Unlike hydrophytes, mesophytes have adapted to form a waxy cuticle since shortage in water supply could be a problem due to the unique niches of these plants. As mesophytes may experience dry periods, they have developed an insoluble waxy cuticle to prevent water from being lost through the top of the leaf [1].
Some mesophytes, as well as xerophytes, also have hairs growing on the leaves. This will be due to the plant’s ecological niche, causing these mesophytes to have this adaptation. The hairs on the leaves are primarily to reduce water loss. When water is evaporated, the vapour condenses on the hairs, effectively trapping the water around the stomata. This creates a micro-climate, effectively reducing the concentration gradient between the inside and the outside of the leaf, resulting in the water evaporating slower, and reducing the amount of transpiration of occurring [13].
In mesophytes, the leaves on the majority of plants are relatively large in size. Since they are found in temperate conditions with sufficient water available, mesophytes can produce big leaves to maximize the surface area for light absorption, which is crucial for photosynthesis to occur, and the survival of the plant. The leaves of some mesophytes also consist of a waxy cuticle. Unlike hydrophytes, mesophytes have adapted to form a waxy cuticle since shortage in water supply could be a problem due to the unique niches of these plants. As mesophytes may experience dry periods, they have developed an insoluble waxy cuticle to prevent water from being lost through the top of the leaf [1].
Some mesophytes, as well as xerophytes, also have hairs growing on the leaves. This will be due to the plant’s ecological niche, causing these mesophytes to have this adaptation. The hairs on the leaves are primarily to reduce water loss. When water is evaporated, the vapour condenses on the hairs, effectively trapping the water around the stomata. This creates a micro-climate, effectively reducing the concentration gradient between the inside and the outside of the leaf, resulting in the water evaporating slower, and reducing the amount of transpiration of occurring [13].
In xerophytes, it is common for plants to either have extremely small leaves, or even an absence of leaves [2]. Since the habitat of xerophytes is extremely arid, the leaves of these plants are reduced to minimize the surface area across which water can evaporate, and be lost. An example of this can be found on cactus plants, where the leaves have been reduced to spines to minimize the surface area, and in turn to minimize water loss. This means that in order for the plant to survive, it has adapted so photosynthesis occurs in the stem of the plant as opposed to the leaves.
Like mesophytes, xerophytes also have a waxy cuticle, however this differs to the cuticle of mesophytes as it is much thicker and leathery. Due to the ecological niche of xerophytes like the aloe plant, the limited supply of water has resulted in the adaptation of a thick waxy cuticle. By having this, water is being prevented from evaporating through the top of the leaf, so therefore water loss can be reduced.
Like mesophytes, xerophytes also have a waxy cuticle, however this differs to the cuticle of mesophytes as it is much thicker and leathery. Due to the ecological niche of xerophytes like the aloe plant, the limited supply of water has resulted in the adaptation of a thick waxy cuticle. By having this, water is being prevented from evaporating through the top of the leaf, so therefore water loss can be reduced.