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In this article we will discuss about:- 1. Meaning of Hydrophytes 2. Characteristics of Hydrophytes 3. Ecological Adoptations 4. Anatomical Features.
Meaning of Hydrophytes:
Hydrophytes are those plants which live in water and adjust with their surroundings. They either remain fully submerged in the water like Hydrilla, Valisineria, etc. or most of their body parts remain under the water like trapa, lotus, etc. water lilies, sedges, crow foots are other important water plants.
A plant that is adapted to living either in waterlogged soil or partly or wholly submerged in water. Many hydrophytes absorb water and gases over the whole surface and have no stomata like the spiked water milfoil (Myriophyllum spicata), which is completely submerged in water.
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The mechanical and vascular tissue of many hydrophytes is reduced and supports them. They often have large intercellular air spaces in their stems, roots, and leaves to overcome the difficulty of obtaining gases from the water. Hydrophytes that are partially submerged have floating leaves with stomata through which gases can be exchanged as in land plants.
However, to prevent the leaves being flooded with water, the petioles may be very long to adjust easily to changes in water level. In the giant water lily (Victoria regia), the enormous leaves have a vertical rim to prevent them from being flooded. Some species like water crowfoot (Ranunculus aquatilis) have both finely divided submerged leaves and floating leaves with stomata.
Aquatic plants are plants that have adapted to living in aquatic environments (saltwater or freshwater). They are also referred to as hydrophytes or macrophytes. These plants require special adaptations for living submerged in water, or at the water’s surface – the most common adaptation is aerenchyma, but floating leaves and finely dissected leaves are also common. Aquatic plants can only grow in water or in soil that is permanently saturated with water. They are therefore a common component of wetlands.
Aquatic plants can usually be categorized into 4 main types:
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(i) Floating plants
(ii) Deep water plants
(iii) Marginal plants
(iv) Oxygenating plants.
Characteristics of Hydrophytes:
Hydrophytes are aquatic plants that are especially suited for living in aquatic environments. In order to survive, a hydrophyte, also known as an aquatic macrophyte, must either be completely submerged in water, or in some cases be allowed to float on the surface of the water
(i) Water Retention:
Plants require water to survive, plants usually possess the ability to absorb and retain water to keep the plant alive between watering cycles. Because aquatic plants are literally submerged in water at all times, there is no need for the plant to water retention like non-aquatic plants. As such, there is no need for aquatic plants to expend energy to regulate transpiration, which is the loss of water in the plant due to evaporation.
(iii) Flat Leaves:
Some aquatic plants float on the surface of water; most aquatic plants have flat leaves which act as floation to a portion of the plant. An example of such a plant is the water lily, Nymphaea Attraction, which is a beautiful bright red water lily that can have up to a 12 inch diameter leaf.
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(iii) Feathery Roots:
Hydrophtes are supported by water as compared to roots and stem structures; most hydrophtes have roots that are small and feathery. These are designed to take in oxygen from the water, and since the plant is fully submersed in water at all times, there is less need for a long and thick root structure. One plant that has a feathery root is the Salvinia, which is a free-floating aquatic fern.
(iv) Air Sacks:
Many hydrophytes have air sacks (chambers) that help the plant float on the surface of the water. It is important to note that some aquatic plants will float slightly submerged in the water, such as the buttercup. Others, such as water lilies, will float up on top of the surface since their leaves distribute the weight across the surface of the water.
Ecological Adoptations in Hydrophytes:
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A. Roots:
1. Due to availability of plenty of water root system is secondary importance and least significant.
2. Roots absent in Wolfia, Ceratophylum.
3. Poorly developed roots are seen in Hydrilla.
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4. Submerged leaves compensate for roots in Salvania.
5. Root caps are absent in Hydrophytes.
6. Amphibious plants growing in mud will have distinct root caps.
7. Root caps are replaced by root pockets in Pistia.
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8. If present roots are generally fibrous adventitious reduced in lenth unbranched or poorly branched.
9. Balancing roots are present in Pistia, Eichornia.
B. Stems:
1. Stem is long slender and flexible in submerged plants Eg: Hydrilla, Potamogeton.
2. Stem is slender or thick, short and spongy in free floating forms Eg; Eichornia.
3. Stem is a rhizome in rooted plants with free floating leaves Eg: Nymphaea and Nelumbo.
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C. Leaves:
1. In submerged forms leaves are thin long and ribbon like (Eg: Vallisnaria) long and linear.
(Potamogeton) finely dissected (eg; Ceratophylum)
2. Floating leaves are large and flat with wax coating Eg: Nyphaea, Nelumbo and Victoria regia.
3. Largest simple leaves in plant kingdom are present in Victoria regia.
4. Petioles are long flexible and covered with mucilage.
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5. Petioles are swollen and spongy in Eg: Eichornia, Trapa.
6. Hetrophily with submerged, floating and aerial leaves seen in Limniphila, Ranunculus and Sagittaria.
Anatomical Features of Hydrophytes:
1. Cuticle is completely absent in submerged parts of the plants.
2. Cuticle may be present as a thin film on surface of parts exposed to atmosphere.
3. Epidermal cells are with chloroplast useful for absorption and assimilation.
4. Stomata are totally absent in submerged hydrophytes.
5. Exchange of gases takes place through diffusion.
6. Non-functional stomata are seen in Potamageton.
7. Epistomatous leaves (stomata found only on upper surface) are present in hydrophytes with floating leaves Eg; Nelumbo.
8. Mechanical tissues like collenchyma and sclerenchyma are more or less absent
9. Xylem is poorly developed in Hydrophytes as the water absorption takes place all over surface of the plant body
10. Hydrophytes have aerenchyma in all parts of the plants. Aerenchyma proves provides buoyancy to the hydrophytes.
