The Adaptations of Xerophytic & Hydrophytic Plants
CAM Metabolism: Crassulacean Acid Metabolism allows plants to fix at night when temperatures are lower and humidity is higher. The stomata remain closed during the day to prevent massive water loss while the stored is used for photosynthesis.
Succulence: Specialized parenchyma tissues in leaves or stems store large volumes of water. This allows the plant to survive extended periods of drought by utilizing internal reserves.
Deep or Widespread Roots: Some xerophytes possess extremely deep taproots to reach the water table, while others have shallow, wide-reaching root systems to capture moisture from light rainfall immediately.
Aerenchyma Tissue: Large, interconnected air spaces in the leaves and stems provide buoyancy, keeping the plant near the surface for light. They also act as a reservoir for oxygen and carbon dioxide, facilitating internal gas diffusion.
Stomatal Distribution: In floating plants, stomata are located exclusively on the upper epidermis. This allows for direct gas exchange with the atmosphere rather than the water, where gas diffusion is much slower.
Reduced Support and Transport Tissues: Because water provides natural buoyancy, hydrophytes have very little lignin or structural tissue. Similarly, the xylem is significantly reduced because water is readily available for absorption through all plant surfaces.
Feathery Roots: Roots are often small and feathery, primarily serving as anchors rather than the main site for nutrient uptake, as minerals can be absorbed directly from the water through the foliage.
| Feature | Xerophytes | Hydrophytes |
|---|---|---|
| Cuticle | Very thick and waxy | Very thin or absent |
| Stomata | Sunken, few, or night-opening | On upper surface or absent |
| Air Spaces | Minimal | Extensive (Aerenchyma) |
| Xylem | Highly developed for transport | Greatly reduced |
| Leaf Shape | Small, needles, or rolled | Large, flat, or finely dissected |
Identify the Stressor: When presented with a plant diagram, first determine if the environment is water-scarce or water-abundant. Look for features like 'sunken' vs 'surface' stomata.
Function over Form: Always explain how a feature helps. For example, don't just say 'hairs'; say 'hairs trap moist air to reduce the water potential gradient'.
Xylem Comparison: Remember that xylem is a transport tissue. Xerophytes need it to move scarce water efficiently; hydrophytes don't need it because they are surrounded by water.
Check the Surface: For floating hydrophytes, the upper surface is the only place gas exchange can occur. For submerged plants, stomata are often entirely absent.