Some leaves have special adaptations to dry environments

Plants that remain active during dry periods must have structural adaptations that enable them to survive. The secretion of a heavier cuticle over the leaf epidermis to retard water loss is a common adaptation to dry environments. An even more common adaptation is a dense covering of epidermal hairs. Some species have stomata only in sunken cavities below the leaf surface, which reduces the drying effects of air currents; often these stomatal cavities contain hairs as well (Figure 40.8).

Interior of leaf

Interior of leaf

Dry Environments

Exterior of leaf

40.8 Stomatal Crypts Stomata in the leaves of some xerophytes are located in sunken pits called stomatal crypts.The hairs covering these crypts trap moist air.

Exterior of leaf

40.8 Stomatal Crypts Stomata in the leaves of some xerophytes are located in sunken pits called stomatal crypts.The hairs covering these crypts trap moist air.

Succulence—the possession of fleshy, water-storing leaves—is an adaptation to dry environments. Ice plants and their relatives have fleshy leaves in which water may be stored. Other xerophytes, such as ocotillo, produce leaves only when water is abundant, shedding them as the soil dries out (Figure 40.9). Cacti and similar plants have spines rather than typical leaves, and photosynthesis is confined to the

Ocotillo Disease

40.9 Opportune Leaf Production The ocotillo, a xerophyte that lives in the lower deserts of the southwestern United States and northern Mexico, produces leaves only when there is sufficient water for photosynthesis.

fleshy stems. The spines may reflect incident radiation, or they may dissipate heat. Corn and some related grasses have leaves that roll up during dry periods, thus reducing the leaf surface area through which water is lost. Some trees, such as eucalyptuses, that grow in arid regions have leaves that hang vertically at all times, thus evading the midday sun.

These xerophytic adaptations of leaves minimize water loss by the plant. However, such adaptations simultaneously minimize the uptake of carbon dioxide and thus limit photosynthesis. In consequence, most xerophytes grow slowly, but they utilize water more efficiently than do other plants— that is, they fix more grams of carbon by photosynthesis per gram of water lost to transpiration than other plants do.

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  • Gerda
    What are some leaf adaptations to hydric environments?
    7 years ago

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