What kind of plants are cacti?
Undoubtedly, cacti are the most oddly shaped plants on Earth. Many resemble echinoderms or starfish that live in the seas. Others look like tennis rackets covered in thorns, large decorative vases, or even multi-armed candelabras. Cacti are generally introverted plants: they are neither much affected by hot weather nor do they require special care.
How much drought can cacti endure?
The occasional rainfalls satisfy their need for water for an entire year. Even an entire season without rain barely affects these plants. This is because cacti possess reserve water cisterns capable of meeting all their water needs, even if the drought lasts for a very long time. Indeed, 90-95 percent of the weight of their fleshy stems is water. Cacti are wise enough to use water gram by gram.
What is the structure of cacti like?
Plants endemic to arid regions are called **Xerophytes**. (Cacti form one group of these plants).
As their name implies, xerophytes generally grow in habitats with low rainfall and sandy soil—regions dominated by arid climates.
Due to the sandy nature of the soil, even a small amount of rain immediately filters down into the inner layers of the ground.
Faced with this escape of rainwater from the surface layers deep into the soil, xerophytic plants have resorted to special measures to save themselves from dehydration: Some of these types of plants have exploratory roots that penetrate very deep into the soil.
These types of roots are tasked with finding the necessary water at any cost. In some xerophytes, instead of this type of root distribution, there is a habit of using the existing water meticulously and gram by gram.
In many of these plants, the leaves also serve as water cisterns. We can cite the Century Plant (Agave) and Aloe, which are native to tropical regions, as examples. The Stonecrop (*Sedum*) and Houseleek (*Sempervivum*), plants of the temperate zone, also have cistern-like leaves. But the task of collecting water is generally the job of the stem. All Cacti growing in Mexico, California, and Africa are like this.
According to the research and calculations performed by botanists on this subject, the barrel cactus, one of the best-known of these plants, expends only 35% of the water it stores in a period of 6 years.
A large portion of the fleshy stem tissues of cacti is made up of water-collecting cells. These cells swell when they draw water inside them. In Cacti with fleshy stems, the stem is green. The organs of the plant that perform chlorophyll assimilation are also these fleshy lobes. In other words, the stem takes over the function of the leaf. In cacti, the leaves have transformed into small thorns, or sometimes they are entirely absent. The spiny nature or complete absence of leaves prevents the plant from transpiring, that is, losing water. Furthermore, the spine-shaped leaves also have the function of protecting the plant against animals. Indeed, arid region animals have a great appetite for the water-filled lobes of Cacti to quench their thirst. It is clear that almost the entire struggle for life of plants with fleshy stems is founded on the principle of not losing the water they absorb. To assist this system, nature has created the epidermis layer covering the stems to be quite thick. Moreover, there are very few pores on the epidermis, meaning the possibility of transpiration is greatly reduced.
Separate fine hairs can be seen on the stems of cacti. But these are dead hairs. Dead hairs separate the stem from the hot air and act as a cooling insulator. Whereas, in plants growing in wet regions, such hairs expand the plant’s transpiration surface, as these plants do not need water that much.
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