Prickly Secrets of Desert Plants

Living on only two inches of rain a year/ Fibonacci patterns on cactus/ Trees that look like smoke

Jan 29, 2023

green and brown plant leaves — Photo by qaz farid on Unsplash

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I SOMETIMES WONDER IF PLANTS have a sense of humor. The many forms they take are evidence of nature's adaptive creativity. I saw some weirdly beautiful desert plants on a recent trip to the Coachella Valley in Southern California.

To get there, I drove through the Mojave desert east of L.A., and the sight of Joshua trees (Yucca brevifolia) kept me entertained for miles. Their jointed arms reached for the sky as if rehearsing for a dramatic opera role. Each tree formed a one-in-a-thousand shape. Joshua trees may have inspired the fantastical trees in Dr. Seuss's books for children, but sadly they are now endangered.

cactus plants in desert — Joshua Trees, Photo by Cedric Letsch on Unsplash

Desert plants often grow into strange and unusual forms to adapt to their challenging landscape. Their leaves, if any, are tiny to keep moisture from leaving and they’ve evolved many ways to collect and keep water.

Rainfall in the lower California desert is a meager 2-3 inches/per year, and temperatures can swing 40 degrees F in a day. While winters are mild, summer highs can reach a blistering 120 degrees F, so it takes a tough and savvy plant to adapt and live here.

Growing a tree that looks like smoke

One desert tree passes itself off as a puff of smoke or dried-up branches as if to say, "There's nothing to eat here—pass on by." This short tree, the "Smoke tree,”Psorothamnus spinosus, is highly adapted to the graveled canyons of the lower Colorado desert. It dresses in gray obscurity for most of the year, saving its energy for a burst of purple blooms right when it needs to attract a particular moth for pollination.

I grew up in this desert area where my parents ran a nursery. My father, Bob Williams, was an expert plant propagator, and he took up the challenge of growing smoke trees for his nursery's selection of desert natives in the late 1960s.

Smoke trees are notoriously hard to cultivate, often failing to sprout or developing a fungal disease. He tried growing from cuttings, heating the seeds in the oven, treating them with anti-fungal solutions, and experimenting with different combinations of sandy soil, but nothing consistently worked.

He puzzled over this problem for months until he returned to the canyons to observe the trees in place. It occurred to him that the few baby smoke trees he observed sprouted shortly after rain storms that washed the tiny grain-sized seeds down the canyon through the gravelly sand. Maybe smoke tree seeds required flash-flood conditions to germinate?

He went home, dug out some sandpaper, and scratched the seeds lightly before planting and watering. Success! More baby smoke trees sprouted after their seeds were lightly scraped to mimic a tumble through the canyon rocks. Smoke trees are just one example of how finely-tuned plants are to their own place and conditions.

Cactus that hitch a ride

Desert plants have other strategies for survival and reproduction— think of their ability to be modular or make clones. Cactus and succulents often grow "pups" or jointed parts that can fall off and live independently. In harsh environments like deserts, reproducing from modular parts is often more successful than seeds. And when that modular part is covered with spines, it can't be eaten either.

If you've ever walked near a patch of cholla cactus, you would remember that modularity. The barbed hooks of the cholla grab at any passing animal or human in hopes of catching a ride to grow in a new place.

My dog Louie once found a sticky cholla ball on his fur and tried to remove it with his mouth. My son used quick judgment in taking him to the vet, where our dog spent an hour under anesthesia, having multiple people pull out the fish-hooked spines embedded in his tongue and mouth. The cholla was stubborn, but our dog made a full recovery.

Spines in Fibonacci designs

What role do thorns play on a plant besides discouraging hungry predators from eating them or hitching a ride on an animal? The spines also provide some shade, acting as tiny umbrellas to prevent water evaporation. In addition, they channel precious dew or raindrops down the ribs to the roots.

Cactus growth and thorns often follow a mathematical Fibonacci sequence, a spiral pattern found repeatedly in nature. Fibonacci designs are visible in the spines of the globe-shaped cactus loved by artists and landscape designers. Can you see the whirl of a spinning galaxy in this cactus photo?

There's a name for the study of spines and thorns that grow in a series—acanthochronology. Why study them? Researchers say cactus spines can tell us about the past climatic conditions during the plant's life. Spines also help date the cactus—some live hundreds of years. That fat barrel cactus you walk by in the desert could be at least twice your age!

The "Little torch" that lights up after rains

Another oddly-shaped plant native to rocky, Southwestern deserts is the ocotillo (pronounced oh-koh-TEE-yoh) Fouquieria splendens. Its name means "little torch" after the top clusters of red flowers. It resembles something you might see in a sci-fi story— spiny, narrow stems like arms reaching up to twenty feet tall that appear like dead sticks most of the year, then spring to life for a few weeks with tiny leaves and orange-red flowers after rainfall. It grows where few plants want to live— on the dry, chocolate-colored, steep rocky slopes that bake in hot sunlight.

a large cactus in the middle of a desert — Ocotillo, Photo by Parker Sturdivant on Unsplash

There are many other examples of unusual plants in arid climates, from succulents that look like rocks to trees that photosynthesize through green bark, and more.

Nature serves up endless variety in the plant world, each plant finely tuned to the exact place it calls home. Plants are localists. They know their environment intimately and have found ways to thrive there over millions of years, even under the most challenging conditions. Desert plants have earned my deep respect with their "I've-got-this" attitude towards life. 🌵💚

If you visit the Coachella Valley, be sure to see The Living Desert Zoo and Gardens in Palm Desert, CA. Then, an hour's drive up to the higher desert will take you to Joshua Tree National Monument, a surreal land of shapely boulders, Joshua trees, and a wide-open sky. (The desert is best enjoyed from November through April if you want to avoid high heat.)

Mother E