- Desert Plant Survival
- Adaptations and Survival
- Desert flowers: masters of adaptation
- Popular Desert Wildflowers – Tips On Growing Wildflowers In The Desert
- Growing Wildflowers in the Desert
- California’s second ‘super bloom’ in two years transformed a desert into a wildflower wonderland
- Special Collections
- Wildflowers of the Southwestern Desert
- Yes, it’s possible to grow a beautiful walled flower garden in the California desert
- Serpentine Soils and Plant Adaptations
- What Plants Need and What They Will Tolerate
- Botanical Carnivory
- Getting Along in a Challenging World: Adaptations and Tolerances
- Is it Nurture or Nature?
- Resources and References
- Arches National Park Nature
- Plants and Flowers
- Cryptobiotic Soil
- Woody Plants
- Drought Escapers
- Drought Resistors
- Drought Evaders
- Soil Chemistry
Desert Plant Survival
Adaptations and Survival
To survive, desert plants have adapted to the extremes of heat and aridity by using both physical and behavioral mechanisms, much like desert animals. Plants that have adapted by altering their physical structure are called xerophytes. Xerophytes, such as cacti, usually have special means of storing and conserving water. They often have few or no leaves, which reduces transpiration.
Phreatophytes are plants that have adapted to arid environments by growing extremely long roots, allowing them to acquire moisture at or near the water table.
Other desert plants, using behavioral adaptations, have developed a lifestyle in conformance with the seasons of greatest moisture and/or coolest temperatures. These type of plants are usually (and inaccurately) referred to as perennials, plants that live for several years, and annuals, plants that live for only a season.
Desert perennials often survive by remaining dormant during dry periods of the year, then springing to life when water becomes available.
Most annual desert plants germinate only after heavy seasonal rain, then complete their reproductive cycle very quickly. They bloom prodigiously for a few weeks in the spring, accounting for most of the annual wildflower explosions of the deserts. Their heat- and drought-resistant seeds remain dormant in the soil until the next year’s annual rains.
The physical and behavioral adaptations of desert plants are as numerous and innovative as those of desert animals. Xerophytes, plants that have altered their physical structure to survive extreme heat and lack of water, are the largest group of such plants living in the deserts of the American Southwest.
Each of the four southwestern deserts offers habitats in which most xerophytic plants survive. But each is characterized by specific plants that seem to thrive there. The Great Basin Desert is noted for vast rolling stands of Sagebrush and Saltbush, while in the Mojave Desert, Joshua Trees, Creosote Bush, and Burroweed predominate. The Sonoran Desert is home to an incredible variety of succulents, including the giant Saguaro Cactus, as well as shrubs and trees like mesquite, Paloverde, and Ironwood. The Chihuahuan Desert is noted for mesquite ground cover and shrubby undergrowth, such as Yucca and Prickly Pear Cactus.
Cactus, xerophytic adaptations of the rose family, are among the most drought-resistant plants on the planet due to their absence of leaves, shallow root systems, ability to store water in their stems, spines for shade and waxy skin to seal in moisture. Cacti originated in the West Indies and migrated to many parts of the New World, populating the deserts of the Southwest with hundreds of varieties, such as the Beavertail Cactus and Jumping Cholla.
Cacti depend on chlorophyll in the outer tissue of their skin and stems to conduct photosynthesis for the manufacture of food. Spines protect the plant from animals, shade it from the sun and also collect moisture. Extensive shallow root systems are usually radial, allowing for the quick acquisition of large quantities of water when it rains. Because they store water in the core of both stems and roots, cacti are well-suited to dry climates and can survive years of drought on the water collected from a single rainfall.
Many other desert trees and shrubs have also adapted by eliminating leaves — replacing them with thorns, not spines — or by greatly reducing leaf size to eliminate transpiration (loss of water to the air). Such plants also usually have smooth, green bark on stems and trunks serving to both produce food and seal in moisture.
Phreatophytes, like the mesquite tree, have adapted to desert conditions by developing extremely long root systems to draw water from deep underground near the water table. The mesquite’s roots are considered the longest of any desert plant and have been recorded as long as 80 feet. Botanists do not agree on the exact classification of the three mesquite trees: the Honey Mesquite, Screwbean Mesquite and the Velvet Mesquite, but no one disputes the success of their adaptation to the desert environment. Mesquites are abundant throughout all the southwestern deserts.
The Creosote Bush is one of the most successful of all desert species because it utilizes a combination of many adaptations. Instead of thorns, it relies for protection on a smell and taste wildlife find unpleasant. It has tiny leaves that close their stomata (pores) during the day to avoid water loss and open them at night to absorb moisture. Creosote has an extensive double root system — both radial and deep — to accumulate water from both surface and ground water.
Some perennials, such as the Ocotillo, survive by becoming dormant during dry periods, then springing to life when water becomes available. After rain falls, the Ocotillo quickly grows a new suit of leaves to photosynthesize food. Flowers bloom within a few weeks, and when seeds become ripe and fall, the Ocotillo loses its leaves again and re-enters dormancy. This process may occur as many as five times a year. The Ocotillo also has a waxy coating on stems which serves to seal in moisture during periods of dormancy.
Another example of perennials that utilize dormancy as a means of evading drought are bulbs, members of the lily family. The tops of bulbs dry out completely and leave no trace of their existence above ground during dormant periods. They are able to store enough nourishment to survive for long periods in rocky or alluvial soils. The Desert Lily, also known as the Ajo, is found at a depth of 18 inches or more. Adequate winter rains can rouse it to life after years of dormancy.
The term “annuals” implies blooming yearly, but since this is not always the case, desert annuals are more accurately referred to as “ephemerals.” Many of them can complete an entire life cycle in a matter of months, some in just weeks.
Contrary to the usual idea that deserts are uniformly hot, dry and homogeneous in their lack of plant life, they are actually biologically diverse and comprise a multitude of micro-climates changing from year to year. Each season’s unique precipitation pattern falls on a huge variety of mini-environments. And each year in each of these tiny eco-niches, a different medley of plants bloom as different species thrive.
Desert plants must act quickly when heat, moisture and light inform them it’s time to bloom. Ephemerals are the sprinters of the plant world, sending flower stalks jetting out in a few days. The peak of this bloom may last for just days or many weeks, depending on the weather and difference in elevation. The higher one goes, the later blooms come. Different varieties of plants will be in bloom from day to day, and even hour to hour, since some open early and others later in the day.
Ephemerals such as the Desert Sand Verbena, Desert Paintbrush and Mojave Aster usually germinate in the spring following winter rains. They grow quickly, flower and produce seeds before dying and scattering their progeny to the desert floor. These seeds are extremely hardy. They remain dormant, resisting drought and heat, until the following spring — sometimes 2 or 3 springs — when they repeat the cycle, germinating after winter rains to bloom again in the spring. There are hundreds of species of ephemerals that thrive in the deserts of the American Southwest.
If you examine desert soils closely, you will dispel forever any notion you might have of the desert as a barren environment, for you will likely find dozens of both annual and perennial seeds in every handful of desert soil. In the Sonoran Desert, seed densities average between 5,000 and 10,000 per square meter. The world record is over 200,000 seeds per square meter.
This “seed bank” attests to the remarkable reproductive success of desert flora, made possible by their symbiotic relationship with desert fauna — birds, insects, reptiles and even mammals. Animals aid in both fertilization and dispersion of seeds, assuring the continued profusion and diversity of plant life throughout the deserts of the Southwest. For more information see
Desert Food Chain In depth
Desert Food Chain for the young student
Back to Desert Life
Desert flowers: masters of adaptation
They hoard water, manufacture food at night and con their helpers into working for free.
Beneath their celebrated blooms, desert wildflowers are survivalists — plants that vigorously defend their place in a hard, parched land. Some shed their leaves at the first hint of drought, while others stash water in succulent tissue or shield it from evaporation with delicate hairs. There are tricksters that reproduce by scamming pollinators with false promises of mates and nectar.
Behind its spring flower majesty, the California desert is a laboratory for such dry-weather adaptations.
Desert annuals, the showy blooms that carpet canyons in spring, persist by living fast and dying young. They spend water lavishly to grow broad green leaves and flashy blossoms during rains, and then swiftly go to seed.
“These fast-growing showy annuals grow in the desert when it’s not really a desert,” said Travis Huxman, director of the Steele/Burnand Anza-Borrego Desert Research Center. “They just have to get their life cycles taken care of in really quick order.”
Then there are the old-timers: age-tested cacti and creosote, which can live for decades through clever water-conservation schemes. From nighttime photosynthesis to sophisticated moisture barriers, they employ a host of strategies to make the most of scarce supplies of water.
“Everything is driven by aridity here,” said Kate Harper, a botanist in Borrego Springs. “That’s the driving force. How can I lose as little moisture as possible while still creating the sugar I need to live and grow? How can I grab moisture and keep it?”
Wildflowers are starting to bloom now at Anza-Borrego Desert State Park and other desert locales, and they typically peak in late March and April. While botanists said low rainfall may lessen this year’s display, there’s still plenty of color if you observe closely.
“The trick about looking at desert flowers is to get out of your car, walk out a ways and look at things,” said Judy Gibson, collection manager for the botany department at the San Diego Natural History Museum.
The following is an introduction to some flowers that populate Southern California’s deserts and chaparral shrub lands, focused on how they gain a roothold in rock and sand. Included are some mainstays of the region — plants you can see even in low water years — along with more unusual blooms.
Ferocactus cylindraceus — Stout succulents shaped like their namesake, these plants are experts at retaining water. The thick, cylindrical stem has vertical pleats that expand when the plant absorbs water. This allows the cactus to increase its volume by up to 50 percent in high water conditions and then shrink back in dry weather. Like other cacti, the barrel cactus absorbs carbon dioxide at night through a process called CAM photosynthesis. That means the cactus opens its stomata — pores on its stem that control gas exchange — when the weather is cooler, cutting moisture loss. Its spines also safeguard moisture by shielding it from the wind. In spring, the barrel cactus blossoms with yellow, red or fuchsia flowers.
Justicia californica — The chuparosa reduces water loss by having just a few scattered leaves. It instead depends on its light green stems to photosynthesize. Hummingbirds visit the plant’s flowers, giving it its name — which is based on the Spanish verb “chupar,” meaning to suck. Ancient Greeks used leaves from the Mediterranean variety of chuparosa as decoration for the capital of the Corinthian column.
Fouquieria splendens — With serpentine branches 10 to 20 feet high tipped with flaming red flowers, the ocotillo towers over other desert flora. The ocotillo is drought deciduous: It can sprout leaves almost overnight in wet weather and drop those leaves as soon as the weather turns dry. “If it gets wet, they photosynthesize like crazy, setting up that sugar factory,” said Harper, the botanist in Borrego Springs. The plant is so effective at producing leaves quickly that it can do so without nutrients from its roots. Cut specimens will sprout leaves when soaked in water.
Larrea tridentata — These low-lying shrubs with yellow blossoms are some of the most drought-tolerant plants in North America. Creosote branches die off in dry years. Then cloned sprouts pop up around it, forming creosote rings that can stretch many meters across and live thousands of years. Scientists estimate that a particular “king creosote” in the Mojave Desert is 11,700 years old. Thick, resinous leaves help keep in water, while the plant’s bitter smell and flavor help keep herbivores away. Its flowers rotate after being fertilized, making the petals less obvious and diverting pollinators to the unfertilized flowers.
Wallace’s daisy, whispering bells, desert primrose, common phacelia — Desert annuals are classic spring field flowers. They’re also rock stars of the floral world, taking center stage before fading out. Their strategy is drought avoidance. These ephemeral plants live in seed for most of the year, explode into blossom during wet months and then go to seed again, biding time until their next comeback. Individual flowers have other specialized features, such as fine hairs on their leaves to slow down moisture loss or seed inhibitors that prevent germination until enough rain washes them off. “The seeds are their legacy,” Harper said.
Mohavea confertiflora — Named for its ethereal and pale yellow blooms, this flower has uncommon adaptations. It employs double mimicry, impersonating both a nectar-producing plant and a female bee. The ghost flower looks similar to the blazing star, an unrelated species. The blazing star produces nectar, and the ghost flower rides on its coattails: It entices bees with the promise of nourishment, but without the metabolic expense of actually producing any. The flower also features a red design that resembles a female bee. This fake insect tempts male bees, affording cheap and easy pollination, said Gibson at the San Diego Natural History Museum. “That’s another kind of dirty trick — lure the male bees in with an imitation female bee,” she said.
Popular Desert Wildflowers – Tips On Growing Wildflowers In The Desert
Native desert-dwelling wildflowers are hardy plants that have adapted to arid climates and extreme temperatures. If you can provide all that these wildflowers require in terms of temperature, soil and moisture, there’s no reason you can’t grow desert wildflowers in your garden. Read on for more information about growing wildflowers in the desert.
Growing Wildflowers in the Desert
If you’re interested in growing wildflowers in the desert, or if you’d like to try your hand at xeriscaping with wildflowers, keep in mind that most desert wildflowers tolerate very warm days and won’t grow in cold temperatures. However, temperatures above 85 F. (29 C.) in late winter and early spring may scorch the seedlings.
Desert wildflower plants are adaptable to poor, alkaline soil, but the soil must be well-drained. Loosen the top 1 inch (2.5 cm.) of soil before planting. Ensure the plants receive at least eight hours of sunlight per day.
If the seeds are tiny, mix them with sand or old potting mix to help you distribute them evenly. Don’t cover seeds with more than 1/8 inch (3 mm.) of soil.
Most desert wildflowers need a bit of rain throughout the winter in order to germinate, although too much moisture may rot the plants or wash the seeds away.
Plant desert wildflower seeds directly in the garden in early spring when frost is still possible, or before the first hard freeze in fall.
Once established, these wildflowers require minimal watering. The plants aren’t heavy feeders and no fertilizer is needed. Most desert wildflowers self-seed readily. Some, such as Blackfoot daisy and California poppy, are perennial.
Remove wilted flowers to extend the blooming season.
Popular Wildflowers for Desert Climates
- California poppy
- Arizona poppy
- Blackfoot daisy
- Scarlet or red flax
- Desert plumbago
- Devil’s claw
- Blanket flower
- Desert lupine
- Arroyo lupine
- Desert marigold
- Evening primrose
- Mexican hat
California’s second ‘super bloom’ in two years transformed a desert into a wildflower wonderland
Associated Press Published 12:30 PM EDT Mar 12, 2019
BORREGO SPRINGS, Calif. (AP) — It started with the desert lilies in December. Since then a wave of wildflower blooms has been crescendoing across Southern California’s Anza-Borrego desert in a burst of color so vivid it can be seen from mountain tops thousands of feet above.
Two years after steady rains followed by warm temperatures caused seeds dormant for decades under the desert floor to burst open and produce a spectacular display dubbed the “super bloom,” another winter soaking this year is expected to create possibly an even better show by Mother Nature.
In this Wednesday, March 6, 2019, photo, a man looks on amid wildflowers in bloom near Borrego Springs, Calif. Two years after steady rains sparked seeds dormant for decades under the desert floor to burst open and produce a spectacular display dubbed the “super bloom,” another winter soaking this year is shaping up to be possibly even better. Gregory Bull, AP
Having two super blooms in two years is highly unusual. In California, super blooms happen about once in a decade in a given area, and they have been occurring less frequently with the drought.
The 2017 super bloom was the best seen in the Anza-Borrego Desert State Park in 20 years and drew mass crowds to Borrego Springs, a town of 3,500 that abuts the park.
“There’s just an abundance in where it’s blooming and it’s coming in waves,” said Betsy Knaak, executive director of the Anza-Borrego Desert Natural History Association, which tracks the blooms.
On a recent day, Knaak wandered through swaths of bright yellow and acres of purple outside Borrego Springs. Families, retired couples and college students traipsed into the fields trying to capture the natural wonder in photos.
Stephen Rawding drove out from Carlsbad, north of San Diego, to take photos with his girlfriend after a friend told him it was better than the one in 2017.
“It’s unreal,” Rawding said. “It’s just like they said — so beautiful.”
The setting sun lit up the yellow flowers that contrasted sharply against the brown and copper mountains in the background.
There are tapestries of hot pink Bigelow’s Monkey Flower, purple Sand Verbena, delicate white and yellow Evening Primrose and of course the desert lilies, which bloomed extremely early, opening up in December, signaling a super bloom was possible.
Bright orange poppies are also blanketing the sides of Southern California highways.
In this Wednesday, March 6, 2019, photo, Rene Garcia holds her three-month-old son Brandon amid wildflowers in bloom near Borrego Springs, Calif. Two years after steady rains sparked seeds dormant for decades under the desert floor to burst open and produce a spectacular display dubbed the “super bloom,” another winter soaking this year is shaping up to be possibly even better. Gregory Bull, AP
“It’s a painting of colors at the moment out there in many of the areas,” said Jim Dice, reserve manager of Steele/Burnand Anza-Borrego Desert Research Center, University of California Natural Reserve System.
So far, six times the amount of rain has fallen in the Anza-Borrego desert this weather season compared to last year, Dice said.
If the caterpillars and freezing temperatures stay away, the already gorgeous wave of wildflowers could intensify and light up other areas well into spring.
The state park with 640,000 acres (1,000 square miles) is California’s largest, with hundreds of species of plants including blazing stars and the tall spiny Ocotillo, which are covered in buds that will open to flaming orange-red flowers.
A research associate at Dice’s center recently hiked up to the top of Coyote Mountain and shot a photo of the purple fields 3,000 feet (914 meters) below.
“It was pretty spectacular to see that from up above,” Dice said.
Published 12:30 PM EDT Mar 12, 2019
Wildflowers of the Southwestern Desert
Many desert wildflowers are annuals that bloom in response to adequate rainfall and optimal temperatures. Some years few species bloom, while other years offer a plethora of desert wildflowers. The species included in this collection give a glimpse of some of the more prominent and abundant wildflowers of southwestern deserts.
Printer Friendly: Species List | List with Images | List with QR Tags to Mobile
29 Results: 10 25 50 100 per page
|scientific name||common name(s)||image gallery|
|Baileya multiradiata||Desert Marigold
Showy Desert Marigold
|Calliandra eriophylla||Pink Fairyduster
|Calochortus kennedyi||Desert Mariposa Lily
|Calycoseris wrightii||White Tackstem|
|Echinocereus reichenbachii ssp. reichenbachii||Lace Cactus
Lace Hedgehog Cactus
|Enceliopsis nudicaulis||Nakedstem Sunray
|Eschscholzia californica ssp. mexicana||Mexican Gold Poppy
|Fallugia paradoxa||Apache Plume
Devil’s Walking Stick
|scientific name||common name(s)||image gallery|
29 Results: 10 25 50 100 per page
This site features photographs and descriptions of 467 different southeastern Arizona wildflower and plant species, primarily those of the Sonoran Desert and the areas surrounding the city of Tucson in Pima County.
Southeastern Arizona has an unusually wide variety of plants due to its climate, varied topography, variety of habitats, and its location in the biologically diverse Sonoran Desert and the higher elevation Chihuahuan Desert to the east. Although many of the plants on this site grow in a desert habitat, plants that grow in riparian, upland, and mountain habitats are also included.
The best time to see wildflowers here in southeastern Arizona is either during the spring wildflower season (March through early May) or during the summer wildflower season (late July through early September). Autumn wildflowers will begin blooming here in October as the weather cools a bit, and they will continue blooming until the hard frosts of late November. Scattered wildflowers can be observed here in lower elevation desert areas almost all year-round.
Summers are very hot here in the Arizona desert, and daytime temperatures over 100° F (37.8° C) are quite common. June is especially hot and dry. Thankfully, temperatures are much cooler in the mountains, making them a popular summer retreat for area residents, and since many mountain wildflowers bloom here at this time of year, summer is the best time to observe our many colorful mountain wildflowers.
Still growing is a good way to describe this website, and new plant species will continue to be added as they are photographed and identified. The most recently added Arizona wildflowers and plants are listed below. Whether you live here or are just visiting this scenic part of Arizona, I hope that you will find this site useful!
Yes, it’s possible to grow a beautiful walled flower garden in the California desert
In arid regions around the world, from ancient Greece to Morocco, it is always the small walled space that becomes the living area. Protected from wind, blowing sand and reflected heat, these are places where flowers grow freely with herbs and bulbs. When desert conditions are remedied, some of the most dramatic gardens are hidden behind gates and walls.
That was the model for my Palm Springs entry garden: to let my guests experience this sudden change of temperature when they come through the gate. Shade provided by palms on the east-facing exposure allowed bright and darker spots where various types of plants would grow. The soil here was fine, fertile sand in which every seed germinated.
It is here I’d plant all the amaryllis bulbs from Christmas into a mass of incredible cutting flowers year after year. The Dutch growers sent me many exotic hybrids to try here as well. They all thrived along with the Asiatic lilies I planted on a lark. Lo and behold, they thrived the first year, growing to 4 feet with flowers. While true lilies planted in ground will grow and bloom here the spring after fall planting, the soil becomes so hot over summer that, in direct sun, they tend to gradually decline. Add a few large lily bulbs each year to cycle them in and out for perpetual makeover.
More: Agave’s golden twist: How to make this plant pop in your garden
More: Careful raking in the desert and keeping your pathways beautiful
More: These cactuses bloom in the dead of night. Now’s the time to start planting them
Between large flagstone slabs for standing while tending flowers, I planted 1-gallon hybrid marguerites and all their kin sold in garden centers. They go in the first of the year in full bloom to fill gaps between my salvias and perennials that take time to mature. My preference was for soft pinks and blue-flowered daisies as these colors are rare in desert gardens.
All these plants are particularly lovely blended with wiry fernleaf lavender, Lavandula multifida, with their long, fine stems and blue blossoms. When blended together, you get the same feeling of flower gardens with lots of delicate forms and colors. It lasts only until the high heat comes and our “season” is over. Do it in a different palette each year for perpetual change, which is hard to come by in the succulent milieu.
Here, I tested many hybrids of autumn sage where I could enjoy the color and study their habit every day, in all seasons and weather conditions. Standard red thrives, but the more unusual the new hybrid colors are relative to the species, the weaker they are in extremes of heat and cold. In addition, many failed as some needed too much water, some needed much less and still more couldn’t last the summer. All these gradually died out, leaving me with a reliable palette for color gardens.
This is where I fell in love with the low-mounding, silvery-gray foliage and long-stemmed maroon flowers of Pelargonium sidoides. This is a species native to South Africa unaccustomed to excessive moisture. Like our succulents, it too loves our climate and soils. An unexpected success, it’s perfectly compatible in mixed gardens with its long-lived and dense, low mounds. It’s proven itself here time and time again.
Among the flowers, I also grew oregano and tall purple fennel for its umbelliferous flowers and anise-scented foliage. Chives with their fuzzy pink ball flowers did well under the palms, and I added onion sets to the background for quick green snips for meals.
Despite drought, it’s still possible to grow a beautiful, walled flower garden. Mitigation of desert conditions allows you to spend the glory months from January to the end of May gardening amid the flowers. I did it in my little entry garden and so can you.
The time, expertise, advice, input, and support that these many professionals contributed to the development of AMWUA’s materials is what has made them so successful and so widely embraced. Thanks doesn’t seem sufficient, but thank you.
For providing recommendations and experience that guided the Advisory Group in narrowing the list of plants from the Arizona Department of Water Resources Phoenix AMA Low Water Use/Drought Tolerant Plant List to the 200 featured in the booklet, we would like to acknowledge the following individuals:
Rita Jo Anthony, Wild Seed, Inc
Jonathan Arnold, City of Scottsdale Parks, Recreation, and Facilities
John Augustine, Desert Tree Farm
Louisa Ballard, Arizona State University Arboretum
Cathy Cromell, Phoenix Home and Garden Magazine
Libby Davison, University of Arizona Department of Plant Sciences
Ron Dinchak, Mesa Community College Life Science Department
Wendy Hardy, City of Scottsdale
Jay Harper, Harpers Nurseries and Flower Shops, Inc.
George Hull, Mountain States Wholesale Nursery
Mary Irish, Horticultural Writer/Consultant
Rob Johns, A&P Plant Nurseries
Kirti Mathura, Desert Botanical Garden
Judy Mielke, Logan Simpson Design
Terry Mikel, University of Arizona Cooperative Extension
Ed Mulrean, Ph.D., Arid Zone Trees
Steve Priebe, City of Phoenix Streets Department
Janet Rademacher, Mountain States Wholesale Nursery
Marjie Risk, Arizona Department of Water Resources
Ursula Schuch, Ph.D., University of Arizona Cooperative Extension
Dwayne View, Treeland Nurseries, Inc.
Niko Vlachos, V&P Nurseries, Inc.
Jim Wheat, Jim Wheat’s Landscape Center
For reviewing the final draft of the booklet and offering their professional criticism, comments, and suggestions, we would like to recognize:
Chester Leathers, Ph.D., Professor Emeritus, Arizona State University Microbiology Department
Rita Jo Anthony, Wild Seed, Inc.
Matt Johnson, University of Arizona Desert Legume Program
Janet Rademacher, Mountain States Wholesale Nursery
Steve Priebe, City of Phoenix Streets Department
Cathy Cromell, Phoenix Home and Garden Magazine
A special thanks to our intrepid and talented photographer, Dave Seibert. Over a period of two years, Dave gained unexpected expertise in desert-adapted plants as he persistently hunted down and shot many thousands of images of our 224 plants (along with some that looked an awful lot like them but weren’t quite).
We would also like to recognize the following individuals for their patient efforts in reviewing photos for accurate plant identification and providing assistance in locating plants:
Steve Priebe, now teaching at MCC
Kirti Mathura, University of Arizona Cooperative Extension
Judy Mielke, Landscape Architect
Angelica Elliott, Kristen Kindl, and Jaime Toledano, Desert Botanical Garden
Scott Frische and John Sills, Phoenix Zoo
Jeff Payne and Becky Noth, Boyce Thompson Arboretum
Lauren Belcher, Sonoran Desert Museum
Tohono Chul Botanical Gardens
A shout out to Halperin Creative, our web development team. It’s been great to work with web folks who are also fellow water advocates and plant people.
The first sentence of our publication was inspired by text from Growing Desert Plants from Windowsill to Garden by Theodore B. Hodoba, with permission from the author and the publisher, Red Crane Books.
Plant Adaptations to Arid Environments
By Fritz Kollmann – Water Conservation Garden Crew Leader
It takes a certain degree of tenacity to survive in a climate like ours. Life is not easy in the Intermountain West with blazing sun for most of the summer, and cold, snowy winters with temperatures that dip into the single digits. As 21st century humans, we can just retreat to our climate-controlled buildings, drink a glass of water when we need one, and seek shade when it gets uncomfortably hot—but plants remain in one place and only use the resources that are available.
As plants evolved and colonized the surface of Earth they were forced to develop diverse survival strategies. The plants that developed adaptations to survive in arid environments have produced interesting, beautiful, and strange forms of life in the process. Fleshy-leaved succulents, small desert wildflowers, and shrubs and trees with waxy, leathery, or even tiny leaves all thrive in hot, dry environments with little rainfall. These plants use a variety of strategies to conserve water, reduce transpiration, and get the most out of the scant and often seasonal precipitation.
Most dry regions receive the bulk of their moisture during one or two seasons. Some species of annuals have adapted to this by living only during these short, relatively moist seasons. Small, desert annual flowers such as the desert five-spot (Eremalche rotundifolia), have adapted to germinate, grow, flower, and produce seed in a relatively short period of time. The seeds of many plant species can remain dormant in the soil for several years waiting for the right conditions to germinate. Following wet seasons, desert-adapted annuals will germinate in large numbers, producing incredible carpets of flowers, while in drier years significantly fewer plants will germinate. This strategy ensures the best chance of successfully germinating, growing, and reproducing seed for the next generation.
Succulent plants use several strategies to make the most efficient use of the limited water they receive. Agaves, cacti, ice plants (Delosperma sp.), and other fleshy-leaved plants store water in their leaves or stems. The water they store is so precious that some succulents have developed spines and glochids (small, easily detached, barbed spines), or toxins within their tissues to protect themselves from thirsty and hungry animals.
To further aid in the conservation of valuable stored water many succulents use two additional adaptations, the first being a waxy layer on the surface of the leaves that inhibits water loss. The other adaptation involves a different type of photosynthesis than what is commonly employed by most plants called CAM (Crassulacean Acid Metabolism). These plants typically only open their pores for gas exchange (letting carbon dioxide in while water evaporates out) at night, resulting in significantly less water loss when compared to plants that conduct gas exchange during the day.
Woody plants in the vast shrublands of the Great Basin demonstrate interesting adaptations to the low availability of water as well. When the winter snows have melted off, spring rain showers are a distant memory and the soil begins to bake under the punishing rays of the sun, some plants such as the creosote bush (Larrea tridenta) employ a resinous coating on their leaves to reduce water loss, while others drop their leaves entirely such as the bud sage (Artemesia spinescens).
Curl-leaf mountain mahogany (Cercocarpus ledifolius), and other woody plants in the Wasatch foothills demonstrate their ability to withstand scarce water through the small size of their leaves. Smaller leaves reduce the surface area through which a plant loses water. Some species like the shrubby cinquefoil (Potentilla fruticosa) have developed wooly, hairy leaves in order to reflect some of the light from hitting their leaves, reducing leaf temperatures and water loss.
Most plants take up a significant portion of their water through their roots. Tall trees with large leaves, such as Utah’s native Cottonwood (Populus fremontii) need a significant amount of water in order to survive and reproduce. Cottonwoods tend to grow near water and send their roots deep into the ground to reach the water table, ensuring a consistent supply of water. Some perennial bunchgrasses (little bluestem, Schizachyrium scoparium) can send the roots down five feet or more to find groundwater. Large cacti (saguaro, Carnegiea gigantea) have large networks of shallow roots that enable the plant to quickly absorb precipitation before it has a chance to evaporate from the soil. This works well for cacti because they are then able to store water in their fleshy stems for use long after the surface soil has dried out. They also employ CAM photosynthesis to reduce water loss.
The new Water Conservation Garden, scheduled for completion in late 2016 or Spring 2017, will offer a large variety of plants displaying a wide variety of ways to thrive in low-water situations.
Serpentine Soils and Plant Adaptations
The embedded ultramafic rocks of the ophiolite complex find their way to the surface either by erosion of material above the ophiolite or uplift in the course of tectonic activity.
Depending on the mineralogy and forces operating in the physical or chemical environment (metamorphosis), the broad classification of ultramafic rock can be divided into two rock types: serpentinite and peridotite. Serpentinite is the result of intense deformation caused by the force of crustal movement. The rock develops fractures into which water will flow. This hydration process changes the mineralogy of the rock resulting in the creation of serpentine, a polished, gray-green-black rock. For peridotite, the minerals present in the mantle are retained yielding a warty, red to orange rock. The term “serpentine” is commonly used to include both serpentinite and peridotite.
Once exposed to the elements, serpentine rock weathers to form soil. The resultant soils are a byproduct of the mineralogy of the rock, from which it is formed, but other factors come into play like rainfall, topography, and the length of time the serpentine rock has been exposed. All of these factors result in a tremendous variety of soil types derived from serpentine, yet there are characteristics of serpentine soils in common that have bearing on the plants that occupy these areas and their distinctive plant community.
What Plants Need and What They Will Tolerate
All plants need water at some level and a substrate, like soil, to hold them in place. Plant survival and growth depends on what is in the soil, or the soil’s fertility. Essential nutrients in the soil include nitrogen, phosphorus, and potassium along with calcium, magnesium, and various trace metals such as nickel and iron. These nutrients play a role in development of plant tissue. Not only is the presence of these nutrients important, but respective concentrations are also vital.
Serpentine soils are unique in that they vary notably from the model of soil fertility. To the contrary, serpentine soils house only those plant species that can tolerate extreme conditions, in particular:
- Low amounts of calcium and high amounts of magnesium
- Relatively heavy concentrations of nickel, chromium and other heavy metals
- Low levels of nitrogen and poor nitrogen uptake
While calcium is poorly represented in serpentine soils, its availability to plants is further complicated by high concentrations of magnesium that inhibit calcium uptake. The following table provides comparisons of magnesium (Mg) and calcium (Ca) concentrations across various rock types to illustrate the distinctiveness of ultramafic rock.
From Alexander, E.B. et al. 2007. Serpentine Geoecology of Western North America. Table 8.3 Nutrient Element Concentration in Rocks. Which was from Turkekian, K. K. and K. H. Wedepohl. 1961. Distribution of the Elements in some major units of the earth’s crust. Geological Society of America Bulletin 72: 175-192.
Heavy metals are naturally present as micronutrients, but at high concentrations can alter cell membranes and reduce root growth. The interactions between calcium, magnesium, and such heavy metals as nickel are complex at best, whereby magnesium may block the uptake of calcium, while calcium may reduce effects of excess magnesium, and both magnesium and calcium may reduce toxic effects of the heavy metal nickel.
Nitrogen is primarily derived from decomposed organic material. Organic material in serpentine environments occurs sparingly. The atmosphere is another source of nitrogen but must first be converted to a form usable to plants. Bacteria that form nodules on the roots of certain plants accomplish the conversion of atmospheric nitrogen. Plant species in the genus Ceanothus are known to fix nitrogen (nitrogen fixation) and are common members of the serpentine flora.
Scientists agree that there are no typical serpentine soils and no typical responses by plants to these interactions. Plants that prevail on serpentine soils are those that have developed adaptive strategies to tolerate what most plant will not!
Plants have other ways of obtaining nitrogen in a nitrogen-limited environment, such as eating insects. The California pitcher plant, Darlingtonia californica, is a rare carnivorous plant of serpentine wetland communities. California pitcher plant obtains its nitrogen by decomposing insects captured in the pitcher-shaped leaves. The insects crawl down inside the pitcher where they are trapped by a barrier of downward facing hairs. Bacteria and invertebrates then decompose the trapped insects.
Getting Along in a Challenging World: Adaptations and Tolerances
While there are challenges to the infertility of serpentine soils, all is far from grim living on the edge. Instead of characterizing these environments as “harsh” or the soils as “toxic”, perhaps plants on serpentine don’t need so much calcium, maybe high levels of magnesium is the new essential nutrient, perhaps nickel is distasteful to grazing insects, and it could just be that serpentine plants are actually thriving in their environment.
Tolerances and adaptations range from those at the cellular level to those apparent to the naked eye. High concentrations of nickel are tolerated in some serpentine plants by exclusion, reduced transfer of nickel from root to shoot, or hyperaccumulation. Other plants adapt to a low calcium environment, by selectively up taking this nutrient rather than magnesium.
Morphological adaptations to dry and high light environments (and possible nutrient deficiencies) include fleshy leaves, leaf hairs, and protective pigments. The basal rosette growth form, a common form of serpentine perennials, reduces the incidence of desiccation by locating its leaves close to the ground surface out of the drying influence of the wind.
Plant growth on serpentines is typically stunted. Woody plants that grow to tree height on non-serpentine soils grow in a dwarfed or shrub-like form on serpentine soils.
Growth habit of the rare Arabis aculeolata with basal leaves growing close to the ground surface to protect against drying. Photo by Jennifer Kalt.
Glaucous (white colored) and fuzzy leaves of Eriogonum libertinii combined with the basal rosette growth habit. Photo by Shauna Hee.
Gnarled and stunted Jeffrey pine on serpentine. Is Jeffrey pine “pre-adapted” to tolerate life on serpentines? Photo by Linnea Hanson.
Biotic variables, beyond the morphological or physiological, contribute to the ability some plants possess to find nutrients in a nutrient-limited environment. Mycorrhizal relationships – the relationship between a plant and a fungus under ground – facilitate the scavenging and uptake of nutrients by extending the absorptive surface of the fine roots through development of threads called hyphae. These fungi also produce enzymes that decompose organic matter, a source of nitrogen.
Is it Nurture or Nature?
Some plant species are seldom if ever found on serpentines, others are indifferent meaning they can occur both on, or off, serpentines, yet others are almost entirely restricted to serpentines. These distinctions are undoubtedly the result of evolutionary processes, but what mechanism drives the process? Are plants somehow genetically pre-adapted to life on the edge? Did the selective pressures of life on serpentines further separate these plants from others over time? Is it nurture or nature? Likely both, but for now, it is sufficient to say that growth and survival of species on serpentine is a function of the “serpentine syndrome”, the sum of the response to physical, biological, chemical and temporal factors.
Mt. Eddy serpentine outcrop with tufts of yellow lupine, pink-white flowered waterleaf, and angelica. Photo by Julie Kierstead Nelson.
serpentinite and peridotite – Ultramafic rock consists of magnesium-iron silicate minerals, such as olivine and pyroxene and forms the upper mantle of the earth. The crust (oceanic and continental) is situated above the mantle. The part of the mantle forming the “basement” of the oceanic crust is termed peridotite. Peridotite consists primarily of olivine.
In mountain building areas, peridotite exposed to pressure can subsequently fracture. Water entering the fracture alters the mineralogy of the peridotite to form serpentinite. In serpentinite rock, the olivine and pyroxene alter to form serpentine minerals, such as magnesium silicate, talc, and magnetite. Serpentinite can come in many colors depending on the specifics of the mineralogy.
nitrogen fixation – Plants need nitrogen in relatively large quantities. In serpentine areas, nitrogen via decomposition of organic material is likely limited due to the general paucity of organic biomass in serpentine area.
Atmospheric nitrogen is the more likely contributor in serpentine environments but it must first be converted to a different form before plant uptake. In the serpentine world, this conversion or fixation is primarily the work of bacteria living in nodules on the plants’ roots. Bacteria obtain carbon from the plants and in return provide fixed nitrogen, specifically, ammonia. The greatest potential for nitrogen fixation in serpentine soils is in the root zone of certain legumes (e.g. Lotus or Lupinus spp.) or woody species such as Ceanothus spp.
hyperaccumulation – is the adaptation by plants to high heavy metals such as nickel found in serpentine soils. Nickel taken up in the roots becomes concentrated in leaf tissue. In micrograms/gram Thlaspi montanum, a species in the mustard or Brassicaceae family, concentrates 3833 micrograms in its foliage. Species in the genus Streptanthus spp., also in the Brassicaceae family, ranks second with 2400 to 2800 micrograms. These concentrations are in sharp contrast to other serpentine associated plants sampled in the various studies which contain less than 434 micrograms. (Data from: Alexander, E.B. et al. 2007- Table 8.5, which summarized various studies of trace element concentrations in foliage of California and southwest Oregon plants from serpentine soils.)
serpentine syndrome – a phrase coined by Hans Jenny (1980) to explain plant survival on serpentine as a summed response to several factors: chemical, biological, physical, and temporal.
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Resources and References
Arches National Park Nature
Plants and Flowers
Desert annuals like grasses and wildflowers are adapted to the arid environment in many different ways. These include thick, waxy coverings on leaves and stems which reduce exposure and thus evaporative water loss; small leaves which reduce water loss while the plant transpires or “breathes” and receive less solar radiation; and deep taproots to reach further into the soil or shallow widespread roots that absorb surface water quickly.
Despite these adaptations, most desert wildflowers avoid drought and heat by surviving as seeds or bulbs stored in the soil, sometimes for decades. These seeds will only germinate after significant seasonal rainfall, so wildflower growth in Arches is highly variable year to year. April and May are generally the best months to see wildflowers, then again in early fall if there are a lot of summer monsoons. Some desert plants take advantage of the nights’ cooler temperatures to flower. These evening-blooming plants include evening primrose, sacred datura, sand verbena and yucca.
The yucca and the yucca moth have a fascinating nighttime association. After mating, the female moth gathers pollen from one yucca flower, packs it into a ball, and then flies into the night, locating other yucca flowers primarily by “smelling” with her antenna. She visits several flowers, each time laying some eggs in the base of the pistil and packing some of the pollen from her pollen ball down the pistil for her young to feed on. Thus she fertilizes the yucca flowers. Yucca flowers are only pollinated by yucca moths, and yucca moth young only feed on yucca pollen.
Over 400 kinds of plants grow and flourish in Arches, despite extreme temperatures and low rainfall. Plants play an important role in the Arches National Park ecosystem. Plants have adaptations that put them into three different categories: drought escapers, drought resistors and drought evaders. Drought escapers are plants that take advantage of good growing conditions when they exist. For example, these plants will grow when there is enough water. Seeds of these plants may wait years until there is a rainstorm, and then grow. Many flowers and grasses are in this category. Drought resistors are those plants that have specialized parts that help them survive without much water. Some of these plants have small leaves to reduce water loss through the stomata. Others have spines or hairs on their leaves to minimize evaporation. Yucca plants have a long taproot that helps the plant find water below the reach of other plants. Other drought resistor plants include cacti, mosses and sagebrush.
Drought evaders are plants that live only where there is a lot of water. Springs, rivers and streams are examples of places where there is water in the desert. In Arches National Park, drought evader plants might grow near the Colorado River or in Courthouse Wash. Drought evader plants include cottonwood trees, willows, ferns and even poison ivy! All of these plants require a reliable source of water. The plants at Arches National Park would not be as healthy or numerous without the help of organisms like cyanobacteria. Cyanobacteria live on top of the soil. They have sticky sheaths, which bind to individual grains of sand and absorb water. They are invisible to us when they are young. When they are at least 50 years old, fungi, algae and mosses grow with the cyanobacteria to form a crust. The crust is called Cryptobiotic Soil Crust. The name comes from two Greek words, krypto which means hidden, and bitik (os) which means life.
As the crust builds up nutrients, plants begin to grow. There are various plant communities within the park, including pinyonand juniper woodlands, desert shrublands, grasslands, hanging gardens, and riparian corridors. One would not expect to find a water-loving fern living within a few feet of a cactus, but that is exactly what can happen at Arches National Park because of the diverse communities.
More than most plants, the cactus seems perfectly suited to life in an arid climate. The cactus, especially the saguaro, has become emblematic of the American southwest. Nine species of cactus are found in Arches, though the saguaro is not one of them. Cacti are plants that have succulent stems, pads or branches with scales and spines instead of leaves. Cactus pads are actually modified stems with a waxy coating. The prickly spines are modified leaves that break up the evaporative winds blowing across pad surfaces, and help shade the stem. Root systems are usually broad and shallow, and rainwater is soaked up quickly.
Small rain roots actually grow as soon as soil is moistened by rain, and later dry up. All plants photosynthesize, collecting carbon dioxide through holes in their leaves called “stomata” and converting it into sugar and oxygen. Cacti utilize CAM photosynthesis, a process unique to succulents. In CAM photosynthesis, stomata open only at night when the plant is relatively cool, so less moisture is lost through transpiration. However, photosynthesis also requires sunlight.
The CAM process includes a way of chemically storing the carbon dioxide until the sun comes out, when it can be used to complete the photosynthetic process. Stomata are like windows; they have to be open to let air and water in or out, but sunlight can come in even if they’re closed. Despite their prickly armor, cacti are not immune to predators. Many rodents gnaw on cactus pads, and other mammals, including bears and humans, enjoy the sweet red fruit of the prickly pear.
Cheatgrass (Bromus tectorum) has drastically altered landscapes in Arches and throughout the American west. This annual grass arrived in shipments of European wheat during the late 1800s, and quickly established itself in many areas. Cheatgrass now covers over 100 million acres. Cheatgrass is well adapted to the high desert climate and can out-compete many native plants. This is partially because cheatgrass uses a growth strategy unlike any other in the high desert ecosystem. While most desert plants are dormant during winter, cheatgrass germinates in the fall and spends the winter building roots and storing energy. By early spring, cheatgrass is ready to begin its aboveground growth while other plants are just breaking dormancy. Since this strategy appears so effective, it is interesting that no native plants make use of it.
Scientists explain this in two ways. First, it is possible that climate change has created a new “niche” that no native plants are able to exploit. Secondly, it is also possible that extreme climatic events which native plants can survive might someday wipe out this relative newcomer. In addition to germinating earlier, cheatgrass also uses subsurface water more efficiently and colonizes disturbed areas more quickly. As a result, native grasslands are increasingly rare, especially where wildfires or livestock grazing have occurred. In areas where cheatgrass dominates, both biological diversity and soil health decline. Unfortunately, few animals are known to eat cheatgrass, and scientists have not found any means to control it.
Cryptobiotic soil crust is a living ground cover that forms the foundation of high desert plant life in Arches and the surrounding area. This knobby, black crust is dominated by cyanobacteria, but also includes lichens, mosses, green algae, micro fungi and bacteria.
Cyanobacteria, previously called blue-green algae, are one of the oldest known life forms. It is thought that these organisms were among the first land colonizers of the earth’s early land masses, and played an integral role in the formation and stabilization of the earth’s early soils. Extremely thick mats of these organisms converted the earth’s original carbon dioxide-rich atmosphere into one rich in oxygen and capable of sustaining life.
When wet, Cyanobacteria move through the soil and bind rock or soil particles, forming an intricate web of fibers. In this way, loose soil particles are joined together, and an otherwise unstable surface becomes very resistant to both wind and water erosion. The soil-binding action is not dependent on the presence of living filaments. Layers of abandoned sheaths, built up over long periods of time, can still be found clinging tenaciously to soil particles, providing cohesion and stability in sandy soils at depths up to 10cm.
Nitrogen fixation is another significant capability of cyanobacteria. Vascular plants are unable to utilize nitrogen as it occurs in the atmosphere. Cyanobacteria are able to convert atmospheric nitrogen to a form plants can use. This is especially important in desert ecosystems, where nitrogen levels are low and often limiting to plant productivity.
Soil crusts have other functions as well, including an ability to intercept and store water, nutrients and organic matter that might otherwise be unavailable to plants.
Grasses grow throughout Arches. Individual grasses sprout almost anywhere there is soil. Grasslands form in areas where wind-blown sediment and erosion have created a layer of soil that is several feet thick. Small grasslands form in potholes that have filled with dirt. Most desert grasses can be fit into two groups: bunch and sod-forming. Bunch grasses are classic desert plants that occur in scattered clumps. This growth pattern reduces competition for limited soil nutrients and water. Indian ricegrass and needle-and-thread are bunch grasses. The relatively large ricegrass seeds are rich in protein and were an important source of food for Native Americans.
Needle-and-thread has a sharp seed attached to a wound “thread” that drives the seed into the ground as it unwinds. Both of these grasses are perennial, becoming dormant during droughts. Ricegrass plants have been known to live over 100 years. Sod forming grasses are what most people have in their yards. Galleta and blue grama are sod-forming perennials native to Arches, and usually grow together. Unlike most desert grasses, galleta can withstand heavy grazing and is important forage for bighorn sheep and mule deer. The seed head of blue grama looks like eyelashes. Cheatgrass is a sod-forming grass that was accidentally brought to the United States in the 1800s. This European annual is now established throughout the west and frequently takes over areas disturbed by fire or livestock grazing.
There is a great deal of exposed rock in Arches, and much of it is spotted with multicolored lichens. Lichens usually grow on north-facing surfaces since reduced solar radiation is an advantage for many organisms in the desert. Lichens also colonize healthy, mature cryptobiotic soil crust, and occasionally on live or dead plant material. Many species of lichen are found in Arches. A lichen is actually a simple community of at least two organisms, namely fungi with green algae or cyanobacteria, though sometimes with both. The lichen structure is more elaborate and durable than either fungi or algae alone.
Green algae and cyanobacteria manufacture food via photosynthesis, while fungi provide a buffer against weather and are capable of extracting nutrients from soil and rock. Lichens are well adapted to arid climates. They can carry on food production at any temperature above 32º Fahrenheit. Lichens can absorb more than their own weight of water, and can absorb temporary water like dew almost directly into their algal cells (the water does not need to go through roots and stems as it does in vascular plants).
Many plants benefit from the presence of lichens. The cyanobacterial component of lichens can transform atmospheric nitrogen (unusable to most organisms) into a form that is an essential nutrient for life. This is especially important in desert ecosystems, where lack of nitrogen is known to limit productivity.
Mosses and liverworts are some of the many organisms found in Arches that most people do not associate with deserts. Mosses can tolerate long periods of complete dehydration and occupy a variety of habitats in the park, including exposed rocks, cryptobiotic soil crusts, riparian areas and sometimes trees. They do best in shady canyons, north-facing slopes and at the bases of shrubs. Most liverworts must be near water to survive, and are very rare in the park.
Mosses and liverworts are small, primitive, non-vascular plants. They lack the conductive tissue most plants use to transport water and nutrients. Instead, moisture is absorbed directly into cells by osmosis. The most abundant mosses in Arches can remain dry for years, and will rehydrate in seconds after contact with water. Some species begin photosynthesizing less than one hour after being moistened. There is no complete inventory of mosses and liverworts in Arches.
At least 20 moss species are known to colonize cryptobiotic soil crusts, with Syntrichia caninervis being the most common. Grimmia orbicularis accounts for 80 percent of the moss found on rock surfaces. Like all photosynthetic organisms, mosses are primary producers that build biomass through photosynthesis. They enrich ecosystems with organic matter, forming the basis of the food chain. As a component of cryptobiotic soil crusts, mosses trap airborne soil particles, reduce erosion, retain water and may enhance water infiltration.
Studying the woody plants of Arches is made easy by the fact that, as a rule, they grow rather small and far apart. Limited by lack of water, shrubs and trees must disperse in order to survive. Once established, these desert plants are tenacious. Their roots will split rocks in search of nutrients, and many can live over 100 years. Shrubs and trees are distinguished by their height (a less reliable indicator in the desert) and the number of stems (shrubs have several). Common shrubs include Mormon tea, blackbrush, four-wing saltbush and cliffrose. Mormon tea contains a drug similar to ephedrine, which is used in nasal decongestants and as a stimulant. Blackbrush is important winter forage for desert bighorn sheep, despite its thorny nature. In Arches, tree diversity is greatest in riparian corridors where water is plentiful.
Netleaf hackberry, box elder, Russian olive, tamarisk and Fremont’s cottonwood grow in these areas. Both Russian olive and tamarisk are non-native species that can supplant native trees and significantly alter stream environments. Mixed stands of pinyon pine and Utah juniper cover millions of acres in the southwest, including much of Arches. These trees grow closely associated and dominate the landscape in dry, rocky terrain at elevations between 4,500 and 6,500 feet. As elevation decreases, trees become more scattered and Juniper more common because it is more drought resistant than pinyon. Pinyon pines have crooked trunks, reddish bark and are very slow growing. Trees 4 to 6 inches in diameter and 10 feet tall may be 80 to 200 years old. Their root systems are extensive and often mirror the size of the above ground tree. Pinyons produce compact cones that contain tasty, protein-rich seeds called pinenuts. Pinenuts were a major source of food for Native Americans and are still popular today.
Animals like the bushy-tailed woodrat, the pinyon mouse and the pinyon jay also prize them. The Utah juniper is the classic desert tree. Its twisting, often-dead branches seem to epitomize the struggle of life with little water. When moisture is scarce, a juniper will actually stop the flow of fluids to some outer branches so that the tree has a better chance for survival. Scale-covered leaves and bluish, waxy-coated seeds help the tree conserve moisture.
Desert potholes provide homes to a fascinating array of small organisms and microorganisms. Pothole dwellers have unique adaptations which enable them to survive in this feast or famine environment. Potholes are very easily disturbed. Pothole organisms are sensitive to sudden water chemistry changes, temperature changes, sediment input, being stepped on, and being splashed out onto dry land. Human use of pothole water by swimming, bathing or drinking may change the salinity or pH of a pool drastically. More importantly, this change occurs suddenly, unlike the slow, natural changes to which organisms can adapt.
Hikers should therefore avoid using water in potholes as well as walking through dry ones. While these tiny ecosystems may seem unimportant, they can act as an indicator for the health of the larger ecosystems in which they occur. These pools do not have the ability to counteract acids, so the acid rain caused by industrial pollution may be lethal. Pothole health is monitored at various locations in order to track significant changes in our environment.
Datura (Datura wrightii) produces the largest flower in canyon country. Many visitors are surprised at the amount of vegetation in Arches. Plants are critical components of all ecosystems, and Arches is no exception. Plants capture particulate dust in the air, filter gaseous pollutants, convert carbon dioxide to oxygen, provide animal habitat and possess many raw materials useful to humans. Many adaptations enable plants to survive the extremes of temperature and aridity found in Arches. These adaptations are grouped in three categories: drought escaper’s, drought resistors and drought evaders. Drought escaper’s are plants that make use of favorable growing conditions when they exist. These plants are usually annuals that grow only when enough water is available. Seeds may lie dormant for years if conditions are not favorable. Most grasses are escaper’s, as are wildflowers that bloom after seasonal rains during spring or late summer.
Drought resistors are typically perennials. Many have small, spiny leaves that reduce the impact of solar radiation, and some may drop their leaves if water is unavailable. Spines and hairy leaves act to reduce exposure to air currents and solar radiation, limiting the amount of water lost to evaporation. Cacti, yuccas and mosses are examples of drought resistors. Yuccas have extensive taproots that are able to use water beyond the reach of other plants. Moss, a plant not commonly associated with deserts, thrives because it can tolerate complete dehydration: when rains finally return, mosses green up immediately. Drought evaders, the final group, survive in riparian areas where water is plentiful. Monkey flower, columbine and maidenhair fern are found in well-shaded alcoves near seeps or dripping springs. Cottonwoods and willows require a lot of water, and only grow along river corridors and intermittent streams where their roots can reach the water table easily. Soil chemistry and depth are also important factors that influence where plants grow. Deep soils tend to be covered with grasses. Shrubs like blackbrush and purple sage favor shallow sandy soil, while greasewood and Mormon tea are signs of alkalinity. The dominant plant community in Arches, the pinyon-juniper woodland, colonizes rocky soils and fractured bedrock.
Drought escapers are plants that make use of favorable growing conditions when they exist. These plants are usually annuals that grow only when enough water is available. Seeds may lie dormant for years if conditions are not favorable. Most grasses are escapers, as are wildflowers that bloom after seasonal rains during spring or late summer.
Drought resistors are typically perennials. Many have small, spiny leaves that reduce the impact of solar radiation, and some may drop their leaves if water is unavailable. Spines and hairy leaves act to reduce exposure to air currents and solar radiation, limiting the amount of water lost to evaporation. Cacti, yuccas and mosses are examples of drought resistors. Yuccas have extensive taproots that are able to use water beyond the reach of other plants. Moss, a plant not commonly associated with deserts, thrives because it can tolerate complete dehydration: when rains finally return, mosses green up immediately.
Drought evaders, the final group, survive in riparian areas where water is plentiful. Monkey flower, columbine and maidenhair fern are found in well-shaded alcoves near seeps or dripping springs. Cottonwoods and willows require a lot of water, and only grow along river corridors and intermittent streams where their roots can reach the water table easily.
Soil chemistry and depth are also important factors that influence where plants grow. Deep soils tend to be covered with grasses. Shrubs like blackbrush and purple sage favor shallow sandy soil, while greasewood and Mormon tea are signs of alkalinity. The dominant plant community in Arches, the pinyon-juniper woodland, colonizes rocky soils and fractured bedrock.