The “Gypsophilic” Plants of West Texas: Botanical Wonders in the Desert's Most Austere Landscapes
They're uniquely austere landscapes, in a famously austere region. Across the Chihuahuan Desert, exposures of gypsum create white dune fields, badlands, bleached hills, ridges and flats.
But that austerity conceals a surprise.
A half-century ago, botanists turned their attention to these pockets of harsh terrain – and began to find dozens of new plant species. Far from lifeless moonscapes, the gypsum outcrops are home to their own distinctive flora – unique, highly adapted plant communities.
Research on these “gypsophilic” plants continues. It's providing new insight into the fundamental mechanisms of evolution.
Texas' highest peaks rise dramatically ahead. The desert scrub gives way to dunes and chalky soil. Driving north on Highway 54 from Van Horn, the traveler enters the Gypsum Plain – or Castile Formation. Whitish in color, the gypsum was deposited more than 250 million years ago, by a receding Permian-age sea.
Dr. Michael Powell is a distinguished professor emeritus at Sul Ross State University. He began his teaching career in 1963. And in the mid-60s, he turned his attention to the Castile Formation and other gypsum exposures.
“And I started looking into that,” Powell said, “and driving to some of these places where there were gypsum exposures and collecting plants there, assigning different projects to students. So it just became a whirlwind. We started realizing that there are species that are endemic, adapted to gypsum exposures, that don't occur anywhere else in the world, and they evolved there as different species.”
In a region of unforgiving ground, gypsum soils are uniquely inhospitable. They're typically capped by a hard crust – to germinate, plants have to break that barrier. Gypsum soils are high in sulphur and calcium – and nearly devoid of nitrogen and other nutrients plants generally require.
But here were scores of plants that had overcome those challenges.
There are “gypsovags,” plants that can colonize both gypsum and other soils. But botanists have identified more than 200 true “gypsophiles” – plants that grow only on gypsum.
Gypsum outcrops are often separated from one another by many miles. Some gypsum plants are widespread. There's Tiquilia hispidissima – hairy crinklemat. Growing in mounds, with lovely pink flowers, it's found on gypsum exposures across the region.
But the plant communities on many outcrops contain species that are unique to that location.
In New Mexico, two gypsum outcrops are separated by the Guadalupe Mountains. Both outcrops contains perennial wildflowers known as ringstems. But the flowers of the two plants are different. The two ringstems no doubt share a common ancestor. But in their isolation, they've evolved into separate species.
Sometimes the differences can be dramatic, Powell said.
“So it's obvious that speciation has occurred because they've been isolated,” he said. “It's not just like barely little-bitty differences. Some of the most bizarre, remarkable kinds of morphological differences in species are found on these separate gypsum deposits.”
The Chihuahuan Desert has expanded since the end of the last Ice Age, as our region has grown increasingly arid. Many gypsophiles likely evolved in Mexico – and migrated north as desert conditions expanded.
It's baffling to consider that migration process. What could have carried seeds across the vast distances that separate gypsum exposures?
Powell has speculated that dust devils or winds may have been a factor. But he said it remains a mystery.
“I've seen big whirlwinds all over the desert – look like tornadoes,” Powell said. “You see debris going up, and you see them going for miles, and you see them scouring the ground and picking up all this stuff. Or maybe a strong norther or wind. Those are hypotheses of course. I don't know that there's any evidence of how one thing gets from one place to another.”
Finding a gypsophile in flower, when it can be readily identified, is a matter of serendipity. But botanists continue to find new species across the region.
Mike Moore, a scientist at Oberlin College, is at the forefront of the subject. He's analyzing DNA from the plants. His early results suggest gypsophiles originated some 5 million years – just when drying conditions exposed gypsum across the Southwest.
Gypsum plants embody the tremendous adaptability of life. And they're a reminder – that the desert rewards those who take a closer look.