The Adaptations of Xerophytic & Hydrophytic Plants (OCR AS Biology)

• Xerophytes (from the Greek xero for ‘dry’) are plants that are adapted to dry and arid conditions
• Xerophytes have physiological and structural (xeromorphic) adaptations to maximise water conservation

Xeromorphic Features Table

Photomicrograph and annotated drawing showing the xeromorphic features of a leaf of Ammophilia arenaria (Marram grass)

Hydrophytes

• Plants that are adapted to living in freshwater are known as hydrophytes
• They have evolved specific adaptations that enable them to deal with the challenges posed by living in such an environment
• Excess water uptake is not a major concern for plants as their cells possess a cell wall
  • The cell wall prevents too much water from being absorbed

• The abundance of water in the surrounding environment means there is little need for water transport mechanisms or adaptations that reduce water loss
• The main challenge that hydrophytes face is receiving enough carbon dioxide during the day and enough oxygen during the night
  • Water contains less oxygen and carbon dioxide than the air

• Adaptations that are commonly seen in hydrophytes:
  • Floating leaves: the leaves are thin, flat and have large air spaces inside to give them buoyancy. This keeps them close to the surface of the water where there is more light for photosynthesis
  • Thin waterproof waxy cuticle: it is very thin as there is little need to prevent water loss
  • Stomata located on the upper surface of the leaves: this allows for gas exchange to occur with the air instead of the water
  • Reduced root system: only small roots are required as they can also extract nutrients from the surrounding water through their tissues
  • Reduced veins in the leaves: the xylem is significantly reduced as there is no need to transport water throughout the plant

• A common hydrophyte is the water lily

Adaptations of a hydrophyte