7.2.5—Xerophytic adaptations

Xerophytes are adapted to dry conditions. Their leaf features conserve water by reducing the exposed evaporating surface, increasing resistance to water-vapour diffusion, trapping humid air, or limiting the time when stomata are open.

• Thick waxy cuticle → longer diffusion barrier: A thicker cuticle increases the distance/resistance for water vapour leaving the leaf, so less water is lost through the surface.
• Rolled, curled or folded leaf → smaller exposed surface and humid interior: The outer surface exposed to dry air is reduced, while humid air is trapped inside the roll; the water-vapour gradient is therefore reduced.
• Sunken stomata and fine hairs → humid boundary layer: Stomata sit away from moving dry air and hairs trap moist air near the surface, reducing the diffusion gradient.
• Fewer stomata → fewer exit pores: Reducing pore number limits potential routes for water-vapour loss, although gas exchange capacity is also affected.
• Stomata closed by day and open at night → avoid the driest period: Opening at night and closing during daylight can reduce daytime water loss; the feature changes timing rather than making transpiration impossible.

Mechanism check: feature → altered exposed area, diffusion distance, humidity or stomatal opening → reduced water loss.

Not every xerophytic leaf has every listed feature. Identify the feature actually shown and explain its specific effect on the water-loss pathway; do not infer a complete xerophyte package from one adaptation. Water conservation can also constrain gaseous exchange, so “reduced transpiration” does not mean all plant exchange stops. Staff-only visual brief: annotated leaf cross-section with cuticle, sunken/hairy stomata and rolled humid space; do not generate or bind an image.