DK Science: Plant Survival
Some plants have special features that help them to repel predators. Other plants can survive and even thrive in hostile environments, such as cold and rocky mountains. In areas of little rainfall, plants known as XEROPHYTES have developed special methods for collecting and storing water. Another group of amazing plant survivors are known as HALOPHYTES. They can endure extremely salty regions, such as salt marshes, salt pans, and sand dunes.
Aquatic (water) plants face their own survival problems. A water lily’s flowers either float at the surface or are held high on long stems. The upper surface of each leaf is waxy and repels water. The broad, flat leaves float on the water and are supported by long stalks. The stalks are filled with air chambers supplying oxygen for respiration.
Some plants use disguise to hide from plant-eating animals. Blending in with the background like this is called camouflage. With its fleshy, grey leaves, the pebble plant is difficult to spot against the surrounding pebbles – only its flowers give it away. Most of the time, animals mistake the leaves for real stones, and do not try to eat them.
Plants cannot move away from predators, so they must defend themselves in other ways. Some have thorns or spines. Others have foul-tasting poisons in their leaves. Stinging nettle leaves are covered in fine hairs that are filled with poison. Each hair ends in a swollen, glassy tip. When touched, the tip breaks off, leaving a jagged end that can pierce flesh and inject the poison from the hollow hair.
Known as alpines, mountain plants have to cope with strong sunshine, penetrating frost, and bitterly cold winds. Water may be scarce, too, as there is often low rainfall and thin, frozen soil. Alpines grow in dense cushions, which makes them less exposed. Fine hairs on their leaves reduce water loss and protect them from sun damage.
The bromeliad lives in tropical rainforests. Seeking light, it grows high on the branches of a host tree, using its roots to anchor itself. The bromeliad’s leaves direct any rainwater to the heart of the plant. Plants that fix themselves to other plants like this, but do not draw food from them, are called epiphytes.
Plants that have adapted to cope with dry desert conditions are called xerophytes. Many do not have leaves, which would lose water through evaporation in the heat. Instead they may have defensive spines. Some xerophytes have shallow roots that absorb water quickly after rain. Others have very long taproots that extract water from deep in the ground.
Succulents are plants that have swollen, fleshy parts in which they store water. The best-known succulent plants are cacti like this one. A cactus stores water in its stem and can cope with the driest climates. The thick green stem is also used for photosynthesis, as the leaves have been modified into spines.
Plants that have adapted to live in salty environments are called halophytes. Salt draws water out of the roots of most plants, slowly drying them out. Some halophytes have ways to get rid of excess salt. Others need a salty environment in order to survive. Halophytes are able to grow in salt marshes, shallow coastal waters, dry salt pans, and on sand dunes.
Mangrove trees are halophytes that grow along tropical coasts. Their roots take in salt from the seawater. The salt is carried in the tree’s sap up to old leaves, which are then shed, or to living leaves, which have glands that excrete the salt. Many mangroves have arching roots that are exposed at low tide. These roots have breathing pores for taking in oxygen from the air.
