Plant Adaptations to Dry Environments

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Adaptation: The Basics

Adaptations are changes in life forms over time that improve their potential to survive. In deserts and other arid habitats, plants have adaptations that help them collect and store water, enabling them to withstand long dry periods.

Deserts are open environments where plants can easily access all the air and sunlight they need. The most limited resource in deserts is water. These regions typically receive less than 10 inches (25 centimeters) of precipitation (rain or snow) each year.

Plants that grow well in arid habitats have adaptations that help them:

• Conserve water
• Cope with sun exposure and temperature extremes
• Repel thirsty animals
• Ensure reproduction 

Plants survive in arid environments due to adaptations that include the following.   

Protection from Sun Exposure and Water Conservation Strategies 

• Succulence: Succulent plants come from some of the world’s driest habitats. They store water in the fleshy tissues of their leaves, stems, or roots. This adaptation sustains them during dry periods.

• Reduced Leaves: Small and narrow leaves require less energy to grow than larger leaves, and because they have a smaller surface area, they lose less water through evaporation than large leaves. Conserving water and energy is important for plants in dry habitats.

• Leaves and Stems That Help Create Shade: Many desert plants have stems that stand straight up and leaves that angle downward to minimize the time they face the sun during the hottest part of the day. This also creates shade that helps the plant conserve water.

• Pale Leaves and Stems: Lighter-colored leaves and stems reflect more sunlight and heat than dark leaves, helping protect the plant from overheating. 

• Hairs and Fuzz on Leaves: Hairs on leaf surfaces help plants survive in dry environments in several ways. They trap moisture and increase humidity around the surface of the leaf and stem. They also diffuse light and create shade on the surface of leaves. Some dry habitats can also experience very cold temperatures, and hairs or fuzz protect the plant from frost. 

• Waxy Coatings: Some plants have leaves or stems that produce a pale, waxy substance (epicuticular wax). This coating provides sun protection and prevents plants from drying out. 

• Breathing at Night: Plants exchange gases (carbon dioxide and oxygen) through pores (stomata) on the surfaces of their leaves and stems. In most plants, this occurs during the day as part of photosynthesis. Almost all succulents exchange gases at night when temperatures are generally lower. Cooler temperatures mean they lose less moisture through evaporation. This adaptation (crassulacean acid metabolism) is less efficient than conventional photosynthesis but is more effective overall for plants that need to conserve water. It also explains the slower growth rates of succulents.

Water Collection and Absorption Strategies

• Taproot: A taproot is a single main root (often with smaller, outward roots) that grows into the soil to tap underground moisture.
• Shallow Roots: Some plants have fibrous roots that branch out just beneath the soil surface, forming a dense network that can absorb dewdrops or rain before they evaporate.
• Spines: Some succulents can absorb water through their corky spines, while others have downward-pointing spines that channel water toward the roots where it can be absorbed.

Protection from Animals

• Protection from Hungry Herbivores: Spines and toxic, foul-tasting sap are succulent defense mechanisms that help protect them from thirsty and hungry herbivores.

Growth Patterns

• Spacing: In deserts, plants often live far apart because there isn’t enough water to support them living close together. Plants in the Desert Garden live closer together because gardeners ensure they have extra water and nutrients. 

Why Do So Many Succulents Look Alike? Convergence 

Convergence is a phenomenon in which unrelated life forms from different regions may resemble each other and share features that help them survive in similar environments. Arid habitats can be found on every continent and share similar environmental constraints of limited water. The plants shown here come from different parts of the world, but all store water in fleshy stems, leaves, or roots. 

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