An adaptation is a special feature that helps an organism survive and reproduce in its particular habitat. Plants growing in harsh environments show striking adaptations because they cannot move away from unfavourable conditions.
Xerophytes — plants of dry habitats
Xerophytes, such as cacti and desert grasses, are adapted to reduce water loss by transpiration. Common features include:
- Thick cuticle and reduced leaves (often spines) to lower surface area.
- Sunken stomata in pits, and stomata that open mainly at night.
- Fleshy succulent stems that store water.
- Deep or widely spread roots to absorb the maximum available water.
Example
A cactus stores water in its swollen stem, carries out photosynthesis in the green stem, and has leaves modified into spines that reduce water loss and deter herbivores.
Hydrophytes — plants of watery habitats
Hydrophytes, such as water lily and Hydrilla, live in or on water. Because water is abundant but oxygen and support are limited, they show these features:
- Large air spaces (aerenchyma) that store air and keep the plant buoyant.
- Stomata on the upper surface of floating leaves (or absent in submerged leaves).
- Thin or absent cuticle and poorly developed roots.
- Flexible stems that bend with water currents.
Plants in shaded and other habitats
Plants on the forest floor receive little light, so they have broad, thin leaves with abundant chlorophyll to trap the maximum light. Epiphytes grow on other plants to reach light, while mangrove plants near the sea have breathing roots (pneumatophores) and support roots to cope with soft, oxygen-poor mud and salt water.
Key idea
Adaptations match a plant to its habitat: xerophytes conserve water, hydrophytes stay afloat and obtain oxygen, and shade plants maximise light capture.
Remember
Spines, thick cuticle and sunken stomata = dry habitat. Large air spaces and upper stomata = watery habitat.