Xerophytes :D

Xerophytes: Plants that live in very dry conditions, and have additional adaptations that enable them to conserve water effectively.

Cactus, for example:

• Have a thinner waxy cuticle
• A reduced surface area
• Stem is adapted for photosynthesis, lots of chloroplasts.
  
• Less leaves = low sa/v ratio, which reduces water loss.
  
• Stem stores water in tissues.
  
• Reduced number of stomata, water can't escape from them.
  

These factors increase the rate of transpiration:

• Windy - As water diffuses, a vapour accumulates around the stomata on the outside on the leaf. This increases the water potential, lowering the water potential gradient. Rate of transpiration is therefore, reduced, however, if it is windy, this layer of moisture is blown away, and the area become drier, allowing the water potential to lower, increasing the gradient, and speeding up the rate of transpiration.
• Light- Stomata are open in the light, when the stomata are open, water moves out and into the atmosphere, therefore, light increase rate of transpiration.
  
• Temperature- increases the kinetic energy so particles move faster, and lowers the water potential to make a gradient.
  
• Humidity- low humidity, = less water in air, better WP gradient.
  

Marram Grass:

• Leaf rolls up, only one surface expose, inside gap will be humid, creates gradient.
  
• Expose surface has thick cuticle, and no stoma. (No water can escape)
  
• Stomata on inside in grooves (microclimate, humid, gradient is backward, can't get out.)
• Hairs trap water and increase water potential.