Study of adaptations of Xerophytes and Hydrophytes

Objective 

To study the ecological adaptations in plants living in xeric and hydric conditions.

 

Theory

Let us begin with adaptation 

Adaptations are the changes inside the body of plants and animals to cope with drastic environmental conditions. This concept is central to the theory of evolution, which Charles Darwin famously proposed.   

  1. Natural Selection: Adaptation is often driven by natural selection, a fundamental mechanism of evolution. Organisms with traits that offer advantages in their specific environment are more likely to survive and reproduce, passing those advantageous traits to their offspring. 
  2. Genetic Changes: Adaptations are typically the result of genetic changes that occur over successive generations. These changes can be driven by random mutations in an organism's DNA. Beneficial mutations that confer advantages in a particular environment become more prevalent in a population over time. 
  3. Environmental Pressures: Adaptations are responses to environmental pressures or challenges. These pressures could include changes in climate, the availability of resources, the presence of predators, or other factors that impact an organism's ability to thrive. 
  4. Structural, Functional, or Behavioral Changes: Adaptations can manifest in various ways. They might involve structural changes in an organism's body, such as developing specific physical features. Functional adaptations could include changes in physiological processes, while behavioural adaptations involve alterations in an organism's actions or strategies. 

  Adaptation in xeric (dry) and hydric (wet) conditions refers to organisms' ability to adjust and thrive in environments with varying water availability. In xerophytes, plants and animals grow in arid conditions, whereas, in the case of hydrophytes, they are aquatic plants and animals that thrive in fresh to marine water. 

XEROPHYTES 

  • Modified structures include spines, the presence of hairs, and wax coatings that protect the leaves.  
  • The stem and the roots have high starch levels, which helps in resistance and stability. 
  • It has a thick stem, which helps store more water and photosynthesis. 
  • Have well-developed epidermis and vascular tissue with well-known xylem and phloem components. 

The adaptations of xerophytes include, 

Based on the adaptation, xerophytes are classified as Ephemeral Annuals, Succulents, and non-succulent perennials. 

Ephemeral Annuals:  

  • Found in semi-arid regions.  
  • They have a short lifespan, so these plants are considered "false xerophytes." 
  • For e.g., Gramineae (grasses). 

                                                                                             

 

Succulents: 

  • Commonly found in semi-arid regions and frequently found in locally dry habitats, it includes sea beaches and sandy soils, etc. 
  • They save water as gel with the help of water-storage tissue cells. The Leaves contain spines that reduce transpiration. e Aloe.  
  • Stomata are present on the epidermis of fleshy stems. It remains closed during the daytime and open at night-time to absorb CO2. e.g. Cactus. 
  • Have a well-developed root system that penetrates the surface intensely, is more resistant to high temperature, and absorbs maximum water. e.g., Cactus. 
  • Examples include stem succulents, Cactus, and leaf succulents, including Agave and Aloe. 

                                                  Two Cactus Plants On White Background Illustration Royalty Free SVG,  Cliparts, Vectors, And Stock Illustration. Image 77010890.                                     10 Aloe Vera Health Myths - UnusualSeeds 

Non-succulent perennials:   

  • Generally known as "true xerophytes," they can withstand very high temperatures without water.  
  • The plant possesses a thick stem enveloped by brown, corky bark. e.g., Acacia nilotica. 
  • The leaves are modified as phyllodes, which carry out the photosynthesis. e.g., Acacia melanoxylon. 

                                                          

HYDROPHYTES 

The adaptations of Hydrophytes include,  

  • Leaves are thin and can differ based on their living condition (submergence).  
  • Roots are poorly developed, and they are very thin and short. e.g., Hydrilla, Nymphaea, and Nelumbo or completely absent.  
  • It has a long, slender, and flexible stem. e.g., Hydrilla, Vallisneria, and free-floating forms have a short, thick spongy stem. e.g., Eichhornia. In some cases, the stem is well-developed in the rhizome. e.g., Nelumbo
  • Cell surfaces can help in the absorption of water and minerals. 
  • Have poorly developed vascular system.  
  • Mechanical tissues are poorly developed or absent. 

 

Based on their submergence property, they are classified into three types: Emergent, floating, and submerged. 

Emergent 

  • The plant roots are submerged in water or soil and have a reduced leaf surface.  
  • They were commonly known as helophytes. e.g., Typha, phragmites. 

                                  Typha latifolia | Hole in the Fence  

 

Floating plants 

  • Leaves have a thin, flat structure containing air spaces that give buoyancy.  
  • Free-floating leaves contain smooth wax coatings, which protect from chemical and physical injuries. 
  • Stems are modified into runners or rhizomes. e.g., Nelumbo and Nymphaea. 
  • The petioles are swollen and bulbous, providing a spongy structure that helps the leaves float on the surface. e.g., Eichhornia and Nelumbo.  
  • Epidermal cells contain chloroplasts, which help with photosynthesis and absorb water and nutrients from the surface. 

 

                                                               

Submerged plants 

  • Plants are submerged in water completely. 
  • Have poorly developed root systems and leaves that circulate the stem. Stomata is completely absent. 
  • Leaves are thin and possess long internodes; chloroplasts are absent in epidermal cells. e.g., Hydrilla, Vallisneria, Najas.  
  • The leaf's upper surface is coated with a waxy cuticle.  
  • The stem is long, slender, and flexible to move with water currents.  
  • The hydrophyte leaf and stem contain intercellular air spaces called lacunae or aerenchyma. These small air pockets help in exchanging gases such as oxygen and carbon dioxide. 

                                                             142 Hydrilla Stock Photos and Images - 123RF                                

Learning Outcomes  

Students learn about  

  • Adaptations.  
  • Adaptations of xerophytes.  
  • Adaptations of hydrophytes.