DESERT PLANTS
Few deserts are completely barren. There are often grasses and shrubs that grow far apart (there often isn't enough water to support plants that live close together). During dry periods these plants are brown and seem barely alive. When it rains these plants come alive, often flowering and producing seeds in a short period. A large rain after a long period of drought will cause they the entire desert to bloom.
Most desert plants are drought- or salt-tolerant. Some store water in their leaves, roots, and stems. Other desert plants have long tap roots that penetrate the water table, anchor the soil, and control erosion. The stems and leaves of some plants lower the surface velocity of sand-carrying winds and protect the ground from erosion.
Plant endure the intense heat of desert by making modifications. Many plants have leaves that are almost vertical so they don't face the sun. Some plants excrete a white crust of salt to reflect sunlight away from the leaves Seeds of some desert plants can remain in the sands for decades awaiting a rain to bring them to life.
Plants in the desert have to be able to gather in the little water that is available and store the water so the plant can endure long periods when water is not available. They must also have slow metabolism that allows them that don't use up much water.
Water is absorbed through tiny hairs and rootlets that extend from the plant's roots. The water is supplied to the leaves trough tubes in the stems, branches and/or trunk. If the soil is fertile nutrients are carried to the leaves in the water. In the desert the roots often extend deep into the earth, often to all the way to the water table, many feet below the surface. By contrast rain forest plants have roots are often shallow because water is abundant
In arid regions, sunlight, particularly ultraviolet-B light, is responsible for decomposition. In places where there is plenty of water bacteria usually does the job.
Websites and Resources on Deserts: United States Geological Survey usgs.gov/gip/deserts ; Desert USA (good info on the world’s deserts); desertusa.com/life ; United Nations Global Desert Outlook unep.org/geo/gdoutlook ; Desert Biome article, University of California, Berkeley Desert Biome ; Blue Planet Biomes (about U.S. deserts) blueplanetbiomes.org ; Wikipedia article Wikipedia ;National Geographic online article National Geographic Oxfam Cool Planet oxfam.org.uk/coolplanet ; Sand Dunes article waynesword.palomar.edu ; United States Geological Survey usgs.gov/gip/deserts
Dead Plants Come to Life
David Attenborough wrote: "The first drops of rain are the triggers which bring it to life. Some may fall on clumps of withered dead plants, their leaves brown and fraying to dust, their stems, topped by seed heads, dry and brittle. But suddenly they appear to come to vigorous life, furling back the brown covers of their seed-heads and exposing the seeds within. Others shoot heir seeds several feet into the air."
"But the impression of life is quite illusory. The motive power of these actions in purely mechanical. As rain is absorbed differentially by particular sections of dead tissues, tensions are created which cause some parts to curl and other to release the seeds with a series of tiny explosions."
"But now the seeds themselves, lying on the ground, begin to move. As they also absorb water, the hairs on with which they are covered begin to swell and stiffen, raising the seed upright into such as positions that first rootlets will strike straight downbeats into the ground."
The danger of this methods is the first rains are often brief and the moisture insufficient to promote much growth: thus the seed germinates but then dries and dies. Some seeds are covered by chemical inhibitors that delays the germination process until sufficient rain has fallen.
Types of Desert Plants
Although cacti are often thought of as characteristic desert plants, other types of plants have adapted well to the arid environment. They include the pea family and sunflower family. Cold deserts have grasses and shrubs as dominant vegetation.
Deserts typically have a plant cover that is sparse but enormously diverse. The Sonoran Desert of the American Southwest has the most complex desert vegetation on Earth. The giant saguaro cacti provide nests for desert birds and serve as "trees" of the desert. Saguaro grow slowly but may live 200 years. When 9 years old, they are about 15 centimeters high. After about 75 years, the cacti are tall and develop their first branches. When fully grown, saguaro are 15 meters tall and weigh as much as 10 tons. They dot the Sonoran and reinforce the general impression of deserts as cacti-rich land.
Rain dependent plants live almost their entire life cycle around a period of rain. When there is enough water they grow quickly and then wither and die as the water disappears. The seeds lie dormant, for months or years, until there is sufficient rain to begin the cycle all over again. When the rains come the plants grow and flower soon after the seeds germinates, The desert blooms and is ablaze of color briefly. Then when the moisture is absorbed and the seeds have been released the plants shrivel and die.
Nearly all deserts of the world contains plants with large swollen roots that serve as storage tanks for water. The roots care often hidden underground where they can be exploited by animals. Many desert people rely on plans with swollen roots for sources of water.
Acacia trees grow along dry river banks.
Poplar are oven grown in arid climates because they grow well with little water. The Chinese call them the trees that never died because they may stand for 100 years after they die.
Cacti
Cactuses grow exclusively in the Americas, with hundreds of species found from Chile to Canada. A few varieties have been introduced outside of the Americas. Prickly pears introduced to Australia, Africa and the Mediterranean have adapted so well to their new environments they have expanded over large areas and are regarded as pests.
Cactus have spines rather than leaves. This means they don't loose as much water through transpiration as plants with leaves do. The leaves are small because light is abundant and relatively small amount is necessary to produce of photosynthesis. Many cactuses produce flowers that bloom only at night and are pollinated by bats.
Euphorbias are plants found in Africa that resemble cactuses. They are one of largest groups of flower plants with over 67,000 species. Although cactuses and desert euphorbias are from different families they have similar characteristics. They have no leaves as a means of conserving water. Photosynthesis is carried out in the green stem below a hard waxy surface. The spines deter animals from take the water to eating the stems.
Cactuses and desert euphorbias also have the ability to suck up huge amounts of water when it rains. The deep pleats that run vertically from the stem expand like an accordion causing the trunk to become bloated.
Steppe Plants
Steppes are covered mostly sparse grass or grasses and shrubs such as saxual. Trees are often stunted. Large trunks, branches and leaves require a lot of water to maintain. When the steppes meet the foot foothills, you can find wild poppies, even wild opium poppies.
Plant life is diverse. Many varitoes of gain and grass grow in the steppes in the north. These include feather grass, wormwood and tipachak — an oatlike grass. The summer pasturages are here. Wormwood and grasses dominate the semidesert regions.
Most of Kazakhstan is desert covered by drought resistant bushes, small brush and diferent grasses called salt grass (solyanka). In the snady desrets are are sand wormwood, sage, acacias and haloxyon (saksaul). In th faltland are tugainye woods.
Reeds are found in great numbers around the lakes; Poppies and tulips cover the the foothills of the mountains. Higher up in the mountains are bushes and mixed woods. Higher up still are confinerous forests. In the forests around glacial streams and in alpine and subalpine meadows is where a great variety of animals have traditionally been found.
Steppe Grasses
The grass family is one of the largest in the plant kingdom, embracing some 10,000 different species worldwide. Contrary to what you might think, grasses are fairly complex plants. What you see are only their leaves.
Grass flowers are often not recognizable as such. Because grasses rely on the breeze to distribute pollen (there is a usually lots of wind on the steppe) and they don’t need colorful flowers to attract pollinators such as birds and bees. Grass flowers have scales instead of pedals and grow in clusters on special tall stems that lift them high enough to be carried by the wind.
Grasses need lots of sunlight. They do not grow well in forests or other shady areas. Tall feather grass grows well in the well-watered parts of the steppe. Shorter grass grows better in the dry steppe where there is less rainfall. Chiy, a grass with cane-like reeds, is used by nomads to make decorative screens in the yurts
Grasses can tolerate lack of rain, intense sunlight, strong winds, shredding from lawnmowers, the cleats of Athletes and the hooves of grazing animals. They can survive fires: only their leaves burn; the root stocks are rarely damaged.
The ability of grass to endure such harsh conditions lies in the structures of its leaves, The leaves of other plants spring from buds and have a developed a network of veins that carry sap and expand into the leaf. If a leaf is damaged a plant can seal its veins with sap but do little else. Grass leaves on the other hand don't have a network of veins, rather they have unbranched veins that grow straight, and can tolerate being cut, broken or damaged, and keep growing.
Last updated May 2022
Welwitschia
Worlds’ Longest-Living Plant
Welwitschia is a two-leafed plant that grows in parts of the Namib Desert in southern Africa. It can can live for more than 1,000 years. Richard Sima wrote in the New York Times: “The longest-lived leaves in the plant kingdom can be found only in the harsh, hyperarid desert that crosses the boundary between southern Angola and northern Namibia. A desert is not, of course, the most hospitable place for living things to grow, let alone leafy greens, but the Namib Desert — the world’s oldest, with parts receiving less than 2 inches of precipitation a year — is where Welwitschia calls home. [Source: Richard Sima, New York Times, July 31, 2021]
“In Afrikaans, the plant is named “tweeblaarkanniedood,” which means “two leaves that cannot die.” The naming is apt: Welwitschia grows only two leaves — and continuously — in a lifetime that can last millenniums. “Most plants develop a leaf, and that’s it,” said Andrew Leitch, a plant geneticist at Queen Mary University of London. “This plant can live thousands of years, and it never stops growing. When it does stop growing, it’s dead.”
Some of the largest plants are believed to be more than 3,000 years old, with two leaves steadily growing since the beginning of the Iron Age, when the Phoenician alphabet was invented and David was crowned King of Israel. By some accounts, Welwitschia is not much to look at. Its two fibrous leaves, buffeted by dry desert winds and fed on by thirsty animals, become shredded and curled over time, giving Welwitschia a distinctly octopuslike look. One 19th-century director of Kew Gardens in London remarked, “It is out of the question the most wonderful plant ever brought to this country and one of the ugliest.”
“But since it was first discovered, Welwitschia has captivated biologists including Charles Darwin and botanist Friedrich Welwitsch, after whom the plant is named; it is said that when Welwitsch first came across the plant in 1859, “he could do nothing but kneel down on the burning soil and gaze at it, half in fear lest a touch should prove it a figment of the imagination.”
Genetic Clues on How the Worlds’ Longest-Living Plant Can Live So Long
In a study published in 2022 in Nature Communications, researchers report some of the genetic secrets behind Welwitschia’s unique shape, extreme longevity and profound resilience. Jim Leebens-Mack, a plant biologist at the University of Georgia not involved in the study, said it “gives us a foundation for better understanding how Welwitschia does all the crazy stuff that it does.”
Richard Sima wrote in the New York Times: “The Welwitschia genome reflects the plant’s arid and nutrient-poor surroundings. And its genetic history seems to correspond with environmental history. Approximately 86 million years ago, after a mistake in cell division, the entire Welwitschia genome doubled during a time of increased aridity and prolonged drought in the region — and possibly the formation of the Namib Desert itself, said Tao Wan, a botanist at the Fairy Lake Botanical Garden in Shenzhen, China, and lead author of the study. He said that “extreme stress” is often associated with such genome duplication events. [Source: Richard Sima, New York Times, July 31, 2021]
“Leitch, a co-author of the study, added that duplicated genes are also released from their original functions, potentially taking on new ones. However, having more genetic material comes with a cost, Wan said. “The most basic activity for life is DNA replication," he said, "so if you have a big genome, it is really energy-consuming to maintain life,” especially in such a harsh environment. To make matters worse, a large amount of Welwitschia’s genome is “junk” self-replicating DNA sequences called retrotransposons. “Now that junk needs to be replicated, repaired,” Leitch said.
“The researchers detected a “burst” of retrotransposons activity 1 to 2 million years ago, most likely because of increased temperature stress. But to counteract this, the Welwitschia genome underwent widespread epigenetic changes that silenced the junk DNA through a process called DNA methylation. This process, along with other selective forces, drastically pared down the size and energetic maintenance cost of Welwitschia’s duplicated library of DNA, Wan said, giving it “a very efficient, low-cost genome.”
“The study also found that Welwitschia had other genetic tweaks hidden up its leaves. The average plant leaf grows from the plant’s apexes, or the tippy-tops of its stem and branches. But Welwitschia’s original growing tip dies, and leaves instead pour out of a vulnerable area of the plant’s anatomy called the basal meristem, which supplies fresh cells to the growing plant, Wan said. A large number of copies or increased activity of some genes involved with efficient metabolism, cell growth and stress resilience in this area may help it continue to grow under extreme environmental stress. In a warming world, the genetic lessons that Welwitschia has to offer may help humans breed hardier, less thirsty crops. “When we see that the plant is able to live in this environment for so long and preserve its DNA and its proteins, I really feel like we can find hints for how to maybe improve agriculture,” Leebens-Mack said.
Image Sources: USGS, Wikimedia Commons
Text Sources: "Deserts Geology and Resources" by A.S. Walkers, USGS Online publication; Rick Gore, National Geographic, November 1979 [┵]; New York Times, Washington Post, Los Angeles Times, Daily Yomiuri, Times of London, National Geographic, The New Yorker, Time, Newsweek, Reuters, AP, Lonely Planet Guides, Compton’s Encyclopedia and various books and other publications.