Most known cacti belong to the desert regions, although there a few exceptions. Deserts are regions where there is extremely low rainfall, higher amount of evaporation, and extremely warm weather.
Cacti have unique adaptations that allow them to survive these arid conditions, and these adaptations are the result of the plant having to change itself to meet the changing climatic conditions millions of years ago.
Cacti belong to the ‘succulent’ plant species because all its components, its stems, roots and leaves have the ability to store water, to keep the plant nourished during the drought season.
The defining characteristic of cacti is its many spines (look like thorns). The main way these spines protect the plant is that they prevent herbivorous animals from chewing on them.
The spines also serve as shade for the plant from the harsh sunlight, which helps preserve its internal temperature, without letting it dry too much.
The spines finally serve the vital task of directing rainwater (whenever it does fall) to the plants’ root, thereby not letting precious water go a waste.
Cacti also have the ability to store enormous amounts of water, by opening themselves up to oncoming rain. Therefore, when the heat gets too much, the plant folds itself so that there is less surface area exposed to the sun, thereby reducing the amount of evaporation.
The water that is stored within the plant is not in pure liquid form, but is instead a thick viscous substance. It is safe for human use, and many desert travelers have scratched or made a hole in the columnar of the plant to ‘drink’ it to quench their thirst.
Cacti also have a bluish wax coating over its skin. This ‘glaucus bloom’ is a protective sheath to reduce evaporation, and preserve moisture during the extremely hot season.
Another way that the cacti preserves its moisture is through little holes in the plant called ‘stomata’. They have the additional task of allowing important gases to enter and exit that help the plant survive its harsh environment.
If the cacti do not get enough water, it bends over because the ‘hygroscopic’ (water filled) pressure inside it is low. When the hygroscopic pressure increases, in other words, when it gets enough water, it stands erect again. When the plant is bent over, it has reduced exposure to sunlight, and therefore less moisture is lost from evaporation and it does not die.
One of the cacti’s most prominent adaptations is its root behavior. Its roots grow laterally, meaning they grow wide, often covering about 2 meters in diameter. They do not grow deep, the most being about 10 cms below the surface.
The function of this complicated root system is to provide the plant with a solid anchor to the ground, while gaining maximum minerals and water. These roots, when they grow laterally, they exist in a suspended state until rain activates them.
During rainfall, moisture to these feeding roots makes them separate and they grow out of the main root system, and their sole function is to nourish the plant. During the dry season, these feeder roots die off, thereby allowing the plant to live on the stored water it has collected, and also by not costing the plant extra energy to keep them alive.
There are many types of cacti in the world’s desert regions. The Barrel Cactus, the Crimson Hedgehog Cactus, the Pancake Prickly Pear Cactus, Saguaro Cactus, Ocotillo, and the jumping cholla, are a few of them.
The Jumping Cholla deserves special mention in these as it is the spikiest of all cacti and its main adaptation to surviving predators is that its spikes seem to literally “jump” out and prick anything that tries to touch it.
All these plants are experts at surviving in their harsh environments, although they have slightly different mechanisms to help them live in their unique surroundings.