The saguaro cactus (Carnegiea gigantea) has evolved to meet the demands of a harsh climate. Two of its most noticeable adaptations are the accordion folds and prickly spines running along its green stems. Towering up to 50 feet tall with bent arms, these plants grow wild only in the Sonoran Desert, where temperatures swing from 134 degrees Fahrenheit in the shade to freezing at night.
With spines clustered in groups of roughly 20, saguaros protect their stems from animals searching for food or water. These straight spikes, which grow 2 inches long, emerge from circles called areoles. Despite the spines, animals manage to feed on saguaros, including wasps, ants, mice, bats and bees. Also, woodpeckers and gilded flickers nest inside the cacti.
Saguaro spines point down to channel rain into its folds and to its base. The accordion folds along the stems swell when the plant absorbs water after a rain, allowing it to store moisture for dry periods. Filled with water, these plants can weigh more than 6 tons, according to the National Park Service. Because of their pleats, cacti can expand without damaging their outer layer. However, the skin may split and injure the plant if it takes in too much water.
The saguaro’s folds and spikes help the plant endure summer heat and winter cold. For instance, the pleats shade the stem, protecting it from the intense desert sun, according to the Colorado State University Herbarium. The spines also shade the plants and deflect wind to provide insulation. Arid winds also dry out the cacti.
Photosynthesis occurs in the saguaro's stems because the plant lacks leaves. By expanding the surface area, the folds increase the amount of space where photosynthesis can occur. On these pleats, during the night, pores with valves open to release oxygen and take in carbon dioxide used for photosynthesis. The pleats close with daylight to prevent water loss.
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