Gypsum, and the Plants that Live On It

The mineral gypsum appears all over the world, but is rarely seen on the surface anywhere except in deserts. Gypsum, is a form of Calcium Sulphate in which each CaSO4 molecule is chemically combined with two water molecules in a solid crystalline form. It is more soluble than most other minerals, so it tends to accumulate, and/or be exposed only in very dry environments where it may persist in the form of crusts, geologic layers, or scattered as tiny crystals in the soil. In moderate amounts, it provides plants with two vital nutrients — Calcium and Sulphur. Gypsum is widely used in agriculture as a fertilizer, a soil amendment, and sometimes in treating runoff from irrigated fields.

But what is good in moderate amounts can become undesirable when present in high concentrations. High levels of calcium (Ca) and sulfur (S) can be toxic to many plants. Additionally, ion concentration in gypsic soils can be high enough to impede the osmotic flow of water into roots. Moreover, gypsum tends to be deposited on the soil surface where it forms hard surface crusts that prevent seedlings from becoming established.

But as is often the case in nature, some plants have evolved an ability to tolerate gypsum, and a few have even evolved to require it. Those that tolerate gypsum are known as gypsovags; those that require it gypsophiles.

Bicolor Mustard

Bicolor Mustard ~ one of the most common gypsophiles in Brewster County, Texas


Gyp Daisy ~ A Member of the Aster Family

Gypsovags are non-specialist plants that can live on gypsum soils when the physical crust is absent or reduced. They are often stress-tolerant refugees showing a limited ability to counteract the high S, Ca, and Mg concentrations in the soil; moreover, they are not particularly good at extracting the limited amounts of N and P that are available. Chemical analysis of their leaves reveals these weaknesses. But their ability to tolerate gypsic conditions gives them a significant evolutionary advantage over other plants competing in the area.

Gypsophiles, on the other hand, are usually widespread and may even be dominant in the region they inhabit. These specialists can germinate on the physical crusts that typify gypsum-laden soils. In addition, they usually have physiological adjustments to help them cope with the chemical limitations imposed by gypsum soils. Many gypsophiles have succulent-like leaves that help them dilute undesirable ions. Others have specialized structures in the roots that block the uptake of undesirable ions. For example, the Mariposa cactus (Echinomastus mariposensis,) is so good at blocking gypsum uptake, gypsum may crystallize on its root surfaces. And many plants show adaptations similar to those used by salt-tolerant plants to sequester and/or excrete gypsum. Almost all gypsophiles are perennials and several generations of plants are frequently found growing together.

Nevertheless, surprisingly little is actually known about gypsophiles. Few studies have been conducted on the subject (and most of those in Spain) and many studies present contradictory conclusions. DNA analysis is probably the most active area of research at present.

Unexpectedly, DNA analysis tells us that each of the gypsophilic floras evolved independently from local plants; gypsum tolerance may well be a latent genetic trait of many of them. Moreover, it appears that some plants may have developed gypsophilic traits repeatedly throughout their evolutionary history.

Not all plant families contain gypsophiles – in fact, most gypsophiles come from just a few plant clades. (A clade is a group of plants that are known to have descended from a common ancestor) and gypsophilic clades tend to contain mostly gypsophilic species. For example the Acleisanthes (trumpet flowers) clade contains 6 distinct groups of gypsophiles. The Namas (crinklemats) have 8 gypsophilic taxa. The Nerisyrenia (Mustards) clade has 11.



Many Crinklemats grow in the Chihuahuan Desert

Most true gypsophiles are not very good at distributing their seeds, so they often become isolated on gypsum outcroppings. There they may grow in great numbers but nowhere else. Plants that occur in numbers but that are limited in geographic scope are known as endemics; many endemic species are quite rare. For example, the newly identified Sophora gypsophyla var guadalupensis occurs only in the Guadalupe Mountains and in a single disjunct site in Chihuahua, Mexico. The past few years have yielded several new species that must be classified as gypsophiles.

My own interest in gypsophilic plants began with the discovery of this little plant on the old government road in Fresno Canyon in the Big Bend Ranch State Park. The year was 2011.


My first sighting of Chihuahuan Ringstem

I couldn’t figure out what it was, and nobody else was able to do so from the photograph. But in 2015 I found one in much better condition and it was blooming!


Anulocaulis leioselenus var lasianthus

It turned out to be Anulocaulis leiosolenus, var lasianthus, or Chihuahuan Ringstem. This plant grows on the rocky gypsic soils found between Big Bend National Park and the Big Bend Ranch State Park. The area begins around Study Butte, includes the Terlingua Ghost town environs, and extends west to the western edge of the state park. Its north/south range is probably little more than 40 miles or so. This a classic rare, endemic, gypsophilic plant!

Because of increasing desertification around the world, I believe we can expect to see increasing attention paid to this unique group of plants as we seek to understand how they deal with difficult environmental conditions.

Posted in General Topics, Plants | Tagged , , | 6 Comments

Lichen Revolution


Lichen on Rocky Ground, Davis Mountains

Back in 2009 I wrote a little article about lichen, those symbiotic organisms that have intrigued biologists for so long. At the time I wrote the piece, it was generally believed that lichen were usually a partnership of two species, a fungus and a bacteria, though some were known to have more than one bacteria in the group. It turns out that this is not true.

You can easily see how this theory came to be so widely accepted by simply looking at a slice of lichen under a microscope. Here you can see the different organisms that cooperate to create a lichen.


Photo from

In this image you can see the photosynthesizing bacteria arranged just beneath the surface to catch the light, while the supporting fungus, here stained blue, lives below.

The species pairings are usually quite specific; for each fungus there is one bacteria that will join with it to create a lichen. It would seem, therefore, that each unique pairing would produce a specific lichen. But this is not always the case – apparently different lichen are sometimes made of the same symbiotes. Moreover lichenologists who have attempted to combine two species known to coexist in real lichen, have not been able to graft the two species together to create a viable lichen. Why?

The situation intrigued Dr. Tony Spiribille who has been studying lichen for over 15 years. He was particularly interested in two North American lichen which contain the same symbiotes, but which are different in several ways. Bryoria fremontii, sometimes called “Tree Hair Lichen” is a dull brown and looks like thick hair.


Byoria fremontii

Bryoria tortuosa is yellow or greenish yellow and has finer threads.


Bryoria fremontii is is edible – Bryoria tortuosa is poisonous.

Thinking that these two lichen must be different in some way, Dr. Spiribille sequenced their DNA. But DNA from the two lichen appeared to be genetically indistinguishable! Clearly a closer look was called for.

Working with another group at the University of Montana, Dr. Spiribille used advanced sequencing technology to run RNA “deep scans” of the two lichen. Surprisingly, the RNA scan revealed the presence of a third species that was present in both lichens. Believing that his samples had somehow been contaminated he repeated the experiment, several times, but the third species always showed up. It is a species of Basidiomycetes fungus, previously unknown. He found that the Basidiomycetes fungus produces the substance that makes B. tormentosa so toxic. B. fremontii has the fungus, but very little of it, so it is safe to eat.

Dr. Spiribille then asked other lichenologists around the world to look for the Basidiomycetes fungus. Amazingly, they found it in every lichen they examined i It has now been found on every continent on earth. Moreover molecular evidence indicates that it has been part of lichen symbioses from the start of this partner’s evolution. Unnoticed for almost 150 years, this single species of fungus appears to play an important role in the lives of lichen everywhere. Dr. Spiribille’s remarkable discovery now points the way to a whole new area of research, one which we didn’t imagine just a few years ago.

Posted in General Topics, Plants | 10 Comments

The Amazing Kangaroo Rat

Kangaroo Rat drawing

Kangaroo Rat

cheek pouches

A Kangaroo Rat with Cheek Pouches Filled with Seeds

The Kangaroo Rat is one of the most remarkable animals in the desert. Neither a rat, nor a kangaroo, the Kangaroo Rat is in the genus Dipodomys and is closely related to mice and gophers, with whom they share the characteristic of having external cheek pouches. They are much larger than pocket mice, however, and can be differentiated by their strong hind feet and small, weak forefeet. All kangaroo rats have exceptionally long tails with a conspicuous white hip stripe running the length of the tail. When in a hurry, kangaroo rats hop, and they can hop very fast indeed – up to 12 miles per hour.

A Kangaroo Rat in its Native Habitat

A Kangaroo Rat in its Native Habitat

Kangaroo rats are certainly “cute.” But what makes them extraordinary is that they do not need to drink water – they can get all the water they need from their food. This approach would not be adequate if kangaroo rats were as profligate with water as other mammals, but kangaroo rats are masters of water conservation. They have several physiological adaptations that serve this end, and they actively behave in ways that contribute to conservation.


Despite the high temperatures of their preferred habitats they have no sweat glands; instead they obtain all of their cooling through respiration. To do the cooling and keep as much water as possible, they have specially modified nasal cavities that act as condensers. As warm air leaves their lungs, it cools and the condensation that results is drawn back and readsorbed by their bodies.

Untitled-6Their high body temperatures allow them to radiate heat more effectively than most animals, and although they have few sweat glands, those they do have are in their feet. The evaporating moisture therefore condenses on the floor of their burrows, and increases the humidity inside.

Kangaroo rats have superb kidneys – probably the most advanced of any animal on earth. Their urine is between 4 and 5 times as concentrated as that of humans. It is almost solid when passed; salts and other metabolites may be concentrated as high as 24 percent, compared to 6 percent in humans.



Kangaroo at Entrance to Burrow

Kangaroo rats build extensive burrows which they use both as home and granary. They cope with daytime desert heat by remaining underground, and foraging above ground only at the coolest times of the night. In periods of extreme cold or low food intake, they can become torpid to reduce energy consumption.

Kangaroo rats plug their burrows during the day and can maintain humidities near 50 percent or higher even while humidities outside may be as low as 5 to 15 percent. The moisture they exhale is then absorbed by the seeds they store, becoming available to them once again when eaten. They are selective in the seeds they gather and store, always taking the moistest seeds available – they are able to distinguish exceedingly small differences in water content.

Baby Kangaroo Rat

Baby Kangaroo Rat

Early researchers thought the kangaroo rat’s diet contained mostly dry seeds. More recent studies that analyzed both cheek and stomach contents have revealed that kangaroo rats consume as many insects as they can, and are also fond of green vegetables. This is particularly true during breeding. In fact, when available, insects and green vegetation make up most of their diets. They also consume large quantities of creosote bush seeds along with cactus, mesquite, and the seeds of many wildflowers. Creosote seeds may make up as much as 37 percent of the food they carry back for storage putting the lie to the notion that nothing eats creosote!

Though some researchers claim that kangaroo rats never drink water, that is not true. They can and do drink water when it’s needed and available. In captivity, kangaroo rats can be stressed to the point that they will even drink sea water – they are the only land animal known that can do that.

These animals are rarely seen, but it is not really that hard to get a glimpse of one. I’ve been able to observe them by waiting near a burrow entrance, after dark (preferably on a night with little or no moon), with a small kerosene lantern. I’ve used peanuts and popcorn to lure them out (I break up the peanuts into small pieces). You have to remain very still as they have superb hearing, and activity outside the burrow may discourage them from coming out. But it’s definitely worth the wait. They really are adorable little creatures!

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More New Arrivals

Botanizers are a bit like birders. They’ll go to great lengths to see a particular plant. This year, West Texas is a paradise for botanizers. Since we are having such a fine year out here, I’m adding wildflower photos as soon as the plants come into bloom so that folks can know what’s blooming right now. Here’s last week’s crop.

Prickly Pear

One of the prettiest Prickly Pears out here.

The Spiny-fruited Prickly Pear is named for its prickly fruits.

Rough Mortonia

Rough Mortonia

Rough Mortonia looks almost crustacian when not blooming, but is covered with tiny cream-colored blossoms now.



I’ve shown this one before. It has good medicine for sore gums.

Rainbow Cactus

Rainbow Cactus

This common Echinocereus blooms in different colors. The blossoms are usually yellow, but this year there’s a lot of salmon-colored flowers.



This spiny shrub puts out bouquets of tiny flowers in many colors. They are particularly nice this year.

Range Ratany

Range Ratany

This plant is showy in a different way. Dark wine-colored flowers contrast distinctly with the yellow soils of the Pen Clays.



There’s no blue in the blossoms of Amsonia longiflora, but the flower buds are tipped with a pale blue just before opening.



Posted in Big Bend Ranch State Park, Plants | 5 Comments

Wildflowers Blooming at the Barton Warnock Center Garden.


Desert wildflowers photographed this morning at the Barton Warnock Center, Big Bend Ranch State Park, Terlingua, Texas

_MG_6141-Nerisyrenia camporum _MG_6144-Perityle vasryi _MG_6154 Dyssodia pentachaeta _MG_6163-Rhus microphylla _MG_6170-Buddleia marrubifolia _MG_6194-Amsonia Longiflora Ephedra antisyphilitica

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The Slender Evolvulus

The rainy season in the Chihuahuan Desert brings out flowering plants of all descriptions. The sheer numbers of Shrubby Senna, Trumpet Flowers, Skeletonleaf Goldeneyes, Broom weed, and other yellow flowers can be so overwhelming that it is easy to overlook the many small wildflowers at our feet.

Evolvulus alsinoides

Evolvulus alsinoides

 One such easily overlooked plant is Slender Evolvulus ( Evolvulus alsinoides), a tiny blue sun-loving morning glory that grows on gravelly soils throughout the mountains of the Big Bend. The stems seldom reach over a foot in length, the leaves are about half an inch long, and the azure blue blossoms are less than a quarter inch in diameter. You’ll need to get close to the ground to enjoy the beauty of this small gem.

Closeup of Evolvulus alsinoides

Closeup of Evolvulus alsinoides

The species grows in many places around the world and is appreciated for its medicinal properties. It is used in East Asia, India, Africa, and the Philippines to treat a variety of medical conditions and has a long tradition of use in Ayurvedic medicine to improve memory and boost intellect; pre-clinical research seems to justify these claims.

The plant’s small size makes it somewhat impractical to harvest for home use, but it is grown as a commercial crop in India and can be bought in quantity from herbal shops that sell Ayurvedic herbs, where it is called Shankhapushpi. Who knows? This tiny plant may one day bring big benefits to aging baby-boomers with failing memories.

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Several years ago in an article on prickly pears I mentioned the most famous of prickly pear parasites, the Cochineal bug. A specially-bred strain of this tiny insect produced the brightest, most permanent red dye in the world. In time, it became Spain’s second most valuable export (after silver). It was worth more than its weight in gold, and the Spanish jealously guarded its secret for over 300 years.

The story of this tiny insect and its impact on modern history is beyond the scope of this little blog, but the book A Perfect Red, by Amy Butler Greenfield tells it in fascinating detail.

So why another post on Cochineal? It’s just because I happene3d to get a decent picture of a cochineal patch the other day and wanted to share it with you. You can easily see the insects near the top of the image and the red spots show the brilliant red color for which they are famous. Incidentally, near the bottom right you can also see one of the plant’s tubercles filled with the tiny spines, called glochids, that plants of the Opuntia family make.

Cochineal on a Prickly Pear

Cochineal on a Prickly Pear

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