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How Do Cacti Live?


How Do Cacti Live?
Cacti are hardy, flowering plants in the caryophyllales order that have evolved to survive in some of the Earth’s driest and most barren landscapes. This unceasing survival is achieved through the specialised tailoring of two main principles: form and function.

First, all cacti have developed optimal forms for retention of internal water supplies (spheres and cylinders), combining the highest possible volume for storage with the lowest possible surface area for loss. This allows cacti to store vast quantities of water for elongated periods – for example, the species Carnegiea gigantea can absorb 3,000 litres in a mere ten days. This ability directly correlates to the typical weather patterns of Earth’s barren, dry environments, where cacti are predominantly found, with little water being deposited for months on end, only for a short monsoon to follow in the rainy season. This optimal structural form also grants much-needed shadow for lower areas of the plant, shielding them from the harsh sunlight.
How Do Cacti Live?

Second, cacti have evolved unique mechanisms and adapted traditional plant functions to grow and thrive. Foremost among these changes are the cacti’s spines, elongated spiky structures that grow out from its central body though areoles (cushion-like nodes). These act as a replacement for leaves, which would quickly die if exposed to high levels of sunlight and high temperatures. The spines have a membranous structure and can absorb moisture directly from the atmosphere (especially important in foggy conditions) and also from deposited rainwater, capturing and absorbing droplets throughout the body’s spiny matrix. In addition, due to the lack of leaves, cacti have evolved so as to undertake photosynthesis directly within their large, woody stems, generating energy and processing stored water safely away from the intense sunlight.
Finally, cacti have modified their root structures to remain standing stable in the brittle, parched earth. Cacti roots are very shallow compared with other succulents and are spread out in a wide radius just below the Earth’s crust. This, in partnership with an intense salt concentration, allows cacti to maximise their access to and absorbability speed of ground water, sucking it up before it evaporates or trickles down deeper into the Earth. For stability, many cacti also extend a main ‘tap root’ further into the Earth, in order to act as an anchor against high winds and interference from animals.