The truth is that all plants that grow in such an ecosystem, including cacti, develop unique characteristics that help them to survive the intense heat and limited water supply.
So, how the cactus is adapted to the desert? The primary reason why cacti survive in that ecosystem is because of their numerous adaptations, which include:
- The leaves of this plant are reduced to needle-like structures referred to as spines that limit water loss, which could occur during the process of transpiration.
- The needle-like leaves act as a self-defence mechanism which protects the plant from predators.
- The stem of the cactus plant is swollen and contain numerous collapsible water-storage cells that store water for a relatively long period
- The stem is green and performs photosynthesis.
- The plant has a shallow root system that absorbs maximum water even during light showers.
- The plant is covered with a thick waxy cuticle that helps to conserve water and protect it from desiccation in the scorching heat.
The cactus family is one of the most easily recognizable plant families in the world. Its beautiful blossoms, thick stems, and unusual shape attract many people to the desert each year. Cacti have a wide range of unique characteristics that help it to endure hot temperatures and limited water supply.
Although cacti are synonymous with the desert, they can also be found in some unlikely places such as the tropical regions of South America, Mexico, and some Caribbean Islands. Typically, cacti can survive for many years in the drought conditions that experience little and infrequent rainfall.
Characteristics of the Cactus Plant that Helps It to Adapt to Desert Climate
The cactus plant can survive in the desert because it has developed mechanisms to absorb a maximum amount of water whenever it rains, store the water for a relatively long period while using it efficiently.
Cacti plants have green and thick-walled stems dominated with a lot of needle-like structures referred to as spines. The main role of these modified stems and leaves is to store water for a reasonably long period and minimize water loss as well.
Whenever it rains, the water is collected and stored in the highly modified stem region. The modified stem of the cactus is referred to as “succulent” since it contains specialized tissues for effective water storage.
The vast majority of cacti have succulent stems that are well adapted to living in arid and semi-arid areas. It is the modified stem that store water other than leaves. The stem of the cactus plant may also be ribbed or fluted in shape.
The prominence of ribs and flutes usually depend on how much water the stem is storing. When full, the ribs are almost invisible, but when the cactus is in short supply of water, the stem shrinks and the ribs become quite visible.
During the prolonged periods of a dry spell, other desert plants tend to drop their leaves and become dormant. However, the cactus plant remains stable and unaffected since it has fixed spines instead of leaves.
The green stem continues to photosynthesize while the waxy coating on the surface of the stem ensures that there is minimal water loss.
The dense network of spines provide shed to the stem of the plant, keeping it cooler than the surrounding air. This is an interesting characteristic that ensures that cacti plants don’t lose water to the surrounding hot and dry air.
Finding Water in the Desert
Water is a basic need for any living organism. Without water, no plant or animal can survive on earth. But, where does the cactus plant find water to help it survive in the desert? Unlike the popular notion that deserts are dry throughout the year, the truth is that these places do experience sporadic rains.
When the little rain falls, the cactus ensures that it absorbs as much water as possible. The plant has adapted in a wide range of ways that help it to accumulate water.
Another essential feature of cacti and other desert plants is that they tend to grow near riverbeds. Whether dry or wet, these areas tend to contain a significant amount of underground water that can help plants with deep roots survive the heat.
The primary function of the taproot is to allow the cactus to penetrate deeper into the subsurface soils that contain moisture. The taproot can extend up to five feet into the soil.
This is the primary reason why some types of cacti, such as the Saguaro and the giant Mexican Cereus develop a long and strong taproot soon after germinating.
Fog is another reliable source of water in deserts whenever the conditions are right for it. Air condenses to form dew that is captured by the cactus spines and hairs and directed to the ground where it is quickly absorbed by the roots.
Modifications to the Root System that Helps the Cactus Plant to Adapt to Desert Climate
The roots of the cactus plant are usually found near the surface and rarely go deep. A cactus plant can have a dense network of fibrous roots that spread out several meters away from the plant.
Whenever it rains, the roots absorb as much water as possible and direct it to the stem region for storage. The quantity of water stored will vary depending on the size and type of the cactus plant. In the famous Saguaro cactus, approximately 800 to 1000 litres of water can be stored during a good rainfall season.
When it rains, the cactus plant can easily shoot out more roots to ensure that there is maximum water absorption. However, during the drought season, the excess roots dry up and break off from the main plant to prevent water loss.
Some types of cacti also have a modified root system that can store water and food. This means that once the stem is full and there is still more water to be absorbed, the roots take up the water storage function.
The Role of the Thick Cuticle
The other essential feature of the cactus that helps it to survive in deserts is the thick cuticle. Just like other succulent plants, cacti have a thick, waxy outer covering that is often referred to as cuticle.
In fact, on some cactus species, the cuticle can be thick enough such that you can easily scratch wax off the plant surface with your fingernail.
The thick cuticle prevents water stored in the plant from evaporation into the atmosphere. It also protects the plant from germs and other microorganisms that may try to attack it from the surface.
Since the plant is covered in a thick waxy cuticle, the only way that it can lose water is through microscopic holes in the plant’s skin known as stomata. The primary purpose of stomata is to let in carbon dioxide that helps the plant to manufacture food.
When the stomata open, water vapor escapes from the plant into the atmosphere. Typically, the stomata open during the day and close at night.
To minimize water loss through the opening of stomata, cacti experience reversed opening and closing of the stomata. This means that the stomata close during the day and open at night.
The Role of Areolas
Areoles are plant structures unique to cacti. They usually appear as woolly or hairy areas on the stem from which spines emerge. They also produce flowers. In Pereskia, one of the common types of cacti, the areolas appear in the axis of leaves (the angle between the leaf stalk and the stem).
In the leafless cacti, the areoles can be found on the raised areas of the stem where the leaf bases would have been. In most cases, areoles are circular or oval and separated into two parts.
The part that is nearer the top of the stem produces flowers while the other part produces spines. In most cases, they are yellow or brown and only produce spines or flowers for a few years before they become inactive.
This is the primary reason why most cacti plants have a relatively fixed number of spines and a few flowers that are mostly produced from the top end of the stem.
How long does it take a cactus to grow? Typically, the cactus plant grows slowly with all the growth occurring at the tip of the plant. It takes between 10 and 70 years for a Saguaro cactus plant to mature and attain a height of about 7 feet tall.
Does cactus die? Just like any other living thing, the cactus plant dies after attaining maturity or even before that. The desert conditions can sometimes be too harsh for cacti to survive. If there is no rain for prolonged periods and the cactus depletes its water reserves, chances of dying are quite high. However, a cactus is rarely killed by predators since it has prickly spines that serve as an effective self-defense mechanism.
How does a cactus plant reproduce? Cacti are flowering plants, which means that they rely on the pollination of their flowers to reproduce. Like any other flowering plant, cacti reproduce sexually depending on the ability of pollen to reach the stigma. They rely on simple pollination methods such as wind transfer.