Adaptations in hydrophyte are of three kinds, ecological, physiological and anatomical. For the survival in an aquatic habitat, hydrophytes modify its structures like leaves, stem, roots and the physiology of the cells to adapt themselves according to the different aquatic habitats like freshwater, marine water, lakes, ponds etc.
The adaptations in hydrophyte depend upon the conditions like temperature, osmotic concentration, toxicity, flow, dissolved oxygen, nutrients etc. of water. All these factors may influence plant growth and reproduction in the hydrophytes.
Content: Adaptations in Hydrophytes
Meaning of Adaptations in Hydrophytes
Adaptation in hydrophytes is a common phenomenon which is necessary for all the aquatic plants to thrive according to the surrounding. As the different plants live in different habitats, they need certain modifications so as to adapt themselves to the changing environment. Similarly, hydrophytes also undergo few changes in its morphology, physiology and anatomy to survive in the different aquatic habitat.
Types of Adaptations in Hydrophytes
In hydrophytes, the major absorbing part, i.e. roots are the less significant structure. Its overall growth is either poorly developed, reduced or absent. The accessory components of root-like root cap and root hairs are generally lacking in floating hydrophytes. In the plant species like Lemna, Ecchorhnia etc. root pocket is present instead of root cap whose function is to maintain the water balance.
Wolffia and Utricularia are the plants where the roots are absent, but Hydrilla comprises poorly developed roots. The emergent forms contain well-developed roots.
In submerged forms comprise an elongated, narrow, cushioned and flexible stem. The stems are wide, small, stoloniferous, narrow, cushioned with extensive parenchyma, floats horizontally in the free-floating hydrophytes, as in Azolla. In rooted floating hydrophytes, a stem functions as a rhizome or runner.
Free-floating hydrophytes consist of leaves that are elongated, slender, flattened, and the upper surface is coated with a waxy cuticle. Submerged hydrophytes contain leaves that are slender, translucent, elongated, fibrillar, straight and finely dissected. In amphibious plants, the leaves are of two kinds (submerged and aerial leaves). The submerged leaves show resistant against potential damage by the water current and absorb dissolved carbon dioxide.
The leaves of emergent hydrophytes resemble with the leaves of terrestrial plants. Aerial leaves are bulbous, lobed in structure and showing features similar to the mesophytic characters by having a wax coating on the upper leaf surface. This waxy coating prevents the leaves of hydrophytes against wilting, physical damage, chemical injuries, blockage of stomata etc. The partly submerged plant possesses different patterns of leaves or shows heterophylly, like in Ranunculus aquatilis.
Shoot system: Stems and leaves can participate in the process of photosynthesis, where the oxygen and carbon dioxide liberated as a result of photosynthesis and respiration, respectively is retained in the air cavities. The hydrophyte plants can make the use of gases like oxygen and carbon dioxide present in the air cavities for future cell activities. Petioles in floating hydrophytes have a huge tendency of regeneration that reasonably controlled by the auxins.
Protective layer: Mucilage canals are composed of mucilage cells, which secreting a lubricating agent, i.e. mucilage to protect the plant body against friction, desiccation, decay etc. by covering the entire plant body.
Food storage: In some hydrophytes like a water lily, the food reserves inside a structure refer as the rhizome.
Osmotic concentration: Hydrophytes possess a low osmotic concentration of the cell sap than the surrounding water.
Transpiration: It is absent in submerged plants while floating, and emergent hydrophytes go through high rate of water loss or transpiration.
Reproduction: The vegetative reproduction commonly occurs in hydrophytes by the propagation of the vegetative structures like runners, stolons, root-tubers etc.
Pollination and dispersal: Both pollination and dispersal of fruits occur by the agency of water. The dispersed seeds and fruits generally remain on the water surface, as they are light in weight.
Other properties: Processes like an exchange of water, nutrients and gases occur by the entire plant surface. Mucilage functions as a lubricating agent by surrounding the submerged parts of hydrophyte and protects it from epiphytes. An aerial part of hydrophyte bears “Hydathodes” that removes the additional water entering into the plant body via endosmosis.
It is present as a thin or a single layer comprising parenchymatous cells that are non-protective in function. The epidermis of the leaves include chloroplasts that participate in the process of photosynthesis.
Mucilage encircles the epidermis of the submerged parts and protects the plant against decay. The hypodermis is either absent or poorly developed. The cuticle is lacking in the submerged parts of hydrophytes but can be present as a thin layer on the aerial parts.
The submerged parts lack stomata, but the upper surface of floating leaves carry stomata that refers as “Epistomatous leaves”. Potamogeton is a hydrophyte consisting of non-functional stomata. The emergent hydrophytes consist of scattered stomata on all aerial parts of hydrophyte plant.
It can define as the air cavities found between the differentiated mesophylls, which allows the convenient diffusion of the gases. The diffused gases travel through the internal gas spaces of young leaves, then forced down to the root by the aerenchyma of the stem as a result of water pressure. Older leaves do not support the pressure gradient, so the gases from the roots expel out through the leaves.
Hydrophytes possess a highly-developed, thin-walled, parenchymatous cortex that helps the plant against mechanical stresses and permits efficient gaseous exchange. The large air cavities occupy its major portion. Hydrophytes comprise starch granules as the primary reserve food material that accumulate inside the cortex and pith.
Hydrophytic plants possess mechanical tissue (sclerenchyma and collenchyma) that completely lacks or develops poorly in floating and submerged parts, but present in aerial or terrestrial parts. Cystoliths or sclereids of variable shapes are present in the tissues of leaves and other plant cells.
Submerged hydrophytes comprise of poorly-developed xylem and tracheids. In contrast, the amphibious plants contain well-developed xylem, which assembles towards the central region. Secondary growth in stems and roots does not occur in hydrophytes. In hydrophytes, the presence of endodermis and pericycle are distinct.
Hydrophytic plants possess undifferentiated mesophyll cells in the submerged leaves and differentiated mesophylls (palisade and spongy mesophylls) with the well-developed air cavities in both floating and emergent hydrophytic leaves.
Therefore, we can conclude that all the living creatures undergo specific changes according to the environmental conditions of the surrounding where they have to live in, whether it is aquatic or terrestrial. Hence, the hydrophytic plants also go through a few modifications in their morphology and physiology to sustain life in an aquatic environment.