How Cacti Survive in the Desert

Deserts receive very little rain, so the plants that grow there must make the most of every drop of water. Cacti are among the most successful desert plants, and several features help them survive long dry periods.

The first is their shape. A cactus stem is thick and often round, which gives it a large space for storing water but a relatively small surface through which water can escape. In addition, most cacti do not have ordinary leaves. Instead, they have spines, which are actually leaves that have changed over millions of years. Spines lose almost no water, and they also protect the plant from thirsty animals.

Cacti also take in carbon dioxide, the gas plants use to make food, in an unusual way. Most plants open tiny holes in their surfaces during the day. Cacti keep these holes closed in the heat of the day and open them at night, when the air is cooler and less water evaporates.

[A] Finally, many cacti have shallow roots that spread out widely. [B] After a rare rainstorm, these roots can quickly absorb large amounts of water before it dries up. [C] The water is then carried to the stem, where it can be stored for months. [D]