Hydrophytes are plants that live in aquatic habitat. Hydrophytes can be divided into two types; fully submerged in water or partially submerged in water. These plants can absorb much water as they live in water habitat. Hydrophytes have various features in order to adapt in the aquatic environment in terms of morphological and anatomical adaptations. The morphological adaptations are divided into roots, leaves and stems. The roots of hydrophytes may be absent or poorly developed as they live in an extremely wet environment. Some hydrophytes do not have root caps and root hairs as to limit the absorption of water. Root pockets at the end of root for floating hydrophytes acts as a balancer and hold the plant from drowning. Some hydrophytes have pneumatophores or breathing roots that grow above the water level because they need oxygen gas. Hydrophytes have stems that are spongy, elongated, thick, flexible and spongy thus it can be bent and not easily damaged by the movement of water. The stems consisted of many aerenchyma cells. Aerenchyma cells can be found in the roots and stems. Aerenchyma cells involved in the process of storing gases which is needed for respiration and give many air spaces to provide buoyancy so that the plant can float on the surface of water. Aerenchyma cells also allow diffusion of water from upper positions of the plant into the roots. Thus, the roots can easily obtained oxygen without depending to the soil. Apart from that, the submerged parts of the hydrophytes are covered by mucilage.
Mucilage protects the plant body and allows frictionless movements in the water. Submerged hydrophytes have finely dissected leaves or long and narrow leaves. This adaptation helps to reduce water resistance. The leaves of the floating plants are broad, leathery and thick. This is because to prevent water to diffuse easily into the plants and this can prevent the plants from drowning. It also creates a large surface area for photosynthesis and absorption. The upper epidermis of the leaves is the place where many stomata can be found to trap maximum sunlight for photosynthesis. Gaseous exchange also takes place in the stomata. The stomata is absent in the lower epidermis as the lower epidermis in contact with water. The chloroplasts that is important for photosynthesis under low light intensities only available to the upper surface of the leaves. This is because the upper leaves are exposed to sunlight. In order to prevent the plant from wilting as well as gives protections from chemical and physical injuries, the leaves of floating plants are covered with wax, smooth and shining. Wax on the leaves also can help to repel rain water and to ensure the stomata are clear and open. Besides, hydrophytes also have tiny hairs on the surface of the leaves. This feature helps the plant to maintain stability on the surface of water and to reduce transpiration rate. In terms of anatomical adaptations, hydrophytes have reduced and increased in some factors to help them adapt with aquatic environment. These factors are protecting structure, mechanical tissue, conducting tissue and aeration. The protecting structure are reduced as the cuticles are absent in the submerged parts of the hydrophytes. Furthermore, the epidermis of the plant does not play its role as protecting organ but act as a photosynthesising organ. The hypodermis of plants is poorly developed and thus cannot protect the plant as hypodermis can create a barrier to prevent the attack of pathogen.
The mechanical tissue is also reduced as the sclerenchyma cells are absent or may be poorly developed in the submerged parts of the hydrophytes as the plants is supported by water. Sclerenchyma cells provide support and give strength to the hydrophytes. The presence of mechanical tissue is also absent in stems and leaf petioles. This factor does not affect the structure of the plant because the plant is supported by water as they live in aquatic environment. Some hydrophytes have the presence of sclereids that play its role as sclerenchyma cell. Apart from that, the conducting or vascular tissue is reduced as the vascular bundles are decreasing in hydrophytes. Hydrophytes lack or do not have xylem because they can easily absorb water, dissolved gases and nutrients from the water around them. The aeration of internal tissue increased due to the presence of parenchyma cells. The parenchyma cells have air chambers which located in the roots, stems and leaves that help in photosynthesis and respiration. The air chambers also store gases, help to increase buoyancy and provide mechanical support.
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