Dry Plants

Saguaros, the large cacti shown here, use different strategies to survive through the dry months. Click for more detail.

The desert is a difficult place to be a plant because of the dry, hot air. To move nutrients up their roots, plants evaporate water from their leaves in a process called transpiration. But in the desert, where water is hard to come by, many plants have adaptations to help save water. The plants can save water a few different ways: they can control the amount of water lost by transpiration, the amount they can get, or the amount they can store. If a plant has adaptations to help them deal with desert weather, we call them xerophytes, a word that means dry plants.

Dealing with the Desert

The desert thorn-apple is an annual plant, meaning it only grows during part of the year, then it produces seeds and dies. The seeds will germinate into a plant the next year. Image by Neelix.

Cactus and other plants that store lots of water to help them through the dry seasons are called succulents. During even light rains, these plants soak up as much water as they can hold, storing the water in large storage areas in roots, leaves, or plant stems.

Some plants only live and grow during the wet season, producing seeds that can tolerate the dry season. These plants are called annuals, because they reappear every year. Thus the adult plant, which loses more water than the seed, avoids the hot and dry conditions of the dry seasons.

Other plants called perennials live for several years, but may go dormant or inactive during the dry season.

Many cacti use sharp spines that help shade the plant and that keep some animals from eating the cacti. Image by William Warby.

A lot of desert plants don’t store a bunch of water or die or become inactive during the dry season. Instead, these plants are able to tolerate or withstand the hottest and driest parts of the year.

A few different tricks help these plants handle the desert conditions. The sharp spines that you see on cactus and some other plants help shade the plant from the sun, keeping it cool. Certain plants like mesquite trees grow very long tap roots, reaching down over 100 feet to reach the groundwater, water stored deep underground.

The Fight for Water

The creosote bush uses toxins to defend the area it uses for water and nutrients. Image by Sue in az.

For some plants, one way to make sure to get enough water is to get rid of the competition—that is, nearby plants. A plant called creosote makes special chemicals, or toxins, that they release into nearby soil. These toxins make it difficult for other plants to grow in that soil. This trick is called allelopathy, and it keeps away plants that would use up the creosote’s water supply.

Images via Wikimedia commons. Additional image by Duff Axsom.