There are four major deserts in North America. The Great Basin runs from central Idaho to northern Arizona. It is a high altitude plateau, with very cold winters, mild summers, and few plant species characterized by big sagebrush, Artimesia tridentata.
The Mohave Desert, a small area covering southern Nevada and southeastern California, is known for its cold, rainy winter season resulting in hard freezes leaving little water available. The Joshua tree, Yucca brevifolia, a yucca variety growing above 3000′, is the tallest plant in the area.
The Chihuahuan Desert, covering the high altitudes of northern Mexico ,is subject to hard freezes from arctic winds scouring its surface. Winter rains occasionally occur supporting a rich diversity of low shrubs and small cacti.
The Sonoran Desert, covering southern Arizona and the Baja Peninsula, has high and low altitudes, hot to mild temperatures, and periodic rainfalls. The winter season, with mild temperatures, does not limit the plant and animal diversity as much as in the other three, colder deserts. The Sonoran Desert, which includes several habitat types, supports a rich variety of species including 2000+ plants, 350+ birds, 100 reptiles, and 30 native fishes.
Desert plants exhibit many similar features that make them well-adapted to the hot, dry conditions of their native habitat. Most are succulents, plants with thick, fleshy stems to retain water for use during hot, dry periods. Plants often have spines in place of leaves to reduce the surface area exposed to wind and heat, greatly reducing water loss from evaporation. Spines also add a layer of protection to prevent animals from eating the plant. Stems are green, containing chlorophyll and water, and this is where photosynthesis takes place. Bloom periods and pollination occur during winter or nighttime when cooler temperatures prevail.
Several distinctive native species characterize North American deserts including cacti, succulents, and other plant varieties with spines. The creosote bush, named for its distinctive antiseptic smell, grows three to nine feet tall and has small yellow flowers. This plant grows in colonies of cloned bushes which may live for long periods as epitomized by the King Clone of the Mohave Desert, estimated to be about 12,000 years old. The century plant, another long-lived plant, is a species of agave noted for its large cluster of wide leaves with spiny edges. The plant may live up to 30 years, but flowers only once, then dies.
Clockwise from top: Prickly pear by Fishfoot, Mar 2018; Prickly pear buds by Diandra Rodriguez, Nov 2011; Prickly pear cacturs in bloom by Stepan Mazurov, May 2009; Prickly pear cactus glochids by Tracie Hall, Nov 2017
Often seen cacti include the prickly pear cactus which is actually a group of several species all native to North America. Modified stems, called pads, are often mistaken as leaves. These store water, photosynthesize food and sugars, and produce flowers. All species grow long, single spines in addition to glochids, clusters of very fine, tiny spines. Glochids are often not noticeable but can be easily detached if brushed against and once lodged in the skin are painful and difficult to remove. The saguaro cactus is another common plant. Its distinctive shape, with a tall central column and “arms” growing at right angles, is easily recognizable as one of the Sonoran Desert’s native species. It is the largest cactus in North America, growing to over 40′ high, and living 100 years or more. White, waxy flowers open only at night to attract bats, its preferred pollinator.
Many natural history museums have excellent displays of plants and animals from world-wide desert biomes, including one of my favorites, the North American desert display at the Jurica-Suchy Nature Museum. In my blog next week, I will introduce some of the notable animals and their adaptations to desert life.
