Why do desert plants like cactus have thick and fleshy stems?

Desert plants like cactus have thick and fleshy stems because these stems store water and help the plant survive in dry conditions. Since deserts receive very little rainfall, storing water is an important adaptation for survival.

The thick stem of a cactus acts like a water reservoir, allowing the plant to use stored water when moisture is not available in the surroundings. Many desert plants also have a waxy outer layer that helps reduce water loss.

In cactus plants, leaves are usually modified into spines to prevent excessive water loss and provide protection. These adaptations allow cactus and other desert plants to grow successfully in hot, dry habitats where many other plants cannot survive.