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 | 9 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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The Yuccas

One of the most distinctive plant families of the desert are the yuccas. They grow throughout the American Southwest, Mexico, and South America. Yuccas were always considered valuable by native tribes who used them for food, fiber, and soap-making. People still gather the edible fruits, eat the flower petals in soups and salads, peel apart the leaves for the long, tough fibers, and boil the roots to make soap. Though uncommon now, you can still buy all of these products in specialty market places.

Though there are 40 – 50 species, only a few are common in the Big Bend region.

Spanish Dagger

One of the most visible yuccas in this region is the Spanish Dagger. At 8 feet or more in height, it is an impressive plant. The leaves are long, thick, and very sharp so be careful when approaching them.

Giant Spanish Dagger

This 21 foot Spanish Dagger may be the tallest in Big Bend Ranch State Park.

Their huge flower heads are quite noticeable in the spring when large numbers of them frequently bloom at the same time. Each flower starts out with a dark wine-colored tip, but it fades to a rich cream color as it opens.

Flower Stalk

Spanish Dagger flower stalks can grow to be almost 3 feet tall and a foot in diameter

 Thompson Yucca (Yucca rostrata)

This is the beauty queen of the yucca tribe. It grows to great heights (20–30 feet), mature ones may have multiple shaggy trunks, and many trunks divide into several branches. The rosettes of leaves at the top, and the tall white flower stalks make a showy spectacle year round.

Thompson Yucca is the most popular yucca for gardeners. Tens of thousands of them have been dug up for resale in nurseries throughout the southwest. The plants are easy to propagate and grow, and they live a long time.

Thompson Yuccas in Bloom

Thompson Yuccas in Bloom

You can distinguish Thompson Yuccas from Spanish Daggers by their leaves. Spanish Dagger leaves are thick and stout, but Thompson Yucca leaves are thin and narrow. Also, they have have horny or saw-toothed edges. A little hook, or “beak” grows on the tip of the fruits, a feature which gives this yucca one of its other popular names, the “Beaked Yucca.”

Soaptree Yucca

Native residents of the Southwest quickly discovered that the juices of the Soaptree Yucca makes an excellent soap. They bathed in it, washed their hair in it, and used it for laundry. It is particularly good for woolens because it does not make the fibers clump like modern soaps and shampoos do. Though the Soaptree Yucca can grow as tall as 30 feet, most are not much taller than a grown adult.

Soaptree Yucca in Bloom

Soaptree Yucca with Seed Pods

The Soaptree Yucca likes higher elevations, so you will probably see more of them in the Big Bend Ranch State Park than you will in the national park. The leaves are long, thin, and have a silvery edge. Also, you will usually find a nest of curly fibers growing near the base of the leaves. The flower heads are not as spectacular as many other yuccas, but the plant has a fine, feathery look to it that gives it a unique beauty.

Yuccas and Moths

Yuccas are pollinated exclusively by yucca moths with whom they have developed a uniquely close relationship. For each kind of yucca, there is one particular yucca moth that pollinates it. Without the moth, the yucca cannot set seed; the moth relies entirely on the yucca for food and shelter. During the day, moths hide inside yucca blossoms, safe from predators. At night, they come out, pollinate the flowers, and lay their eggs.

Moth on flower

Yucca Moth Gathering Pollen

Unlike most moths, yucca moths do not have the long nectar-sipping tongue of their relatives. Instead, the female yucca moth has a set of tiny tentacles around her mouth. She uses the tentacles to gather yucca pollen which she then rolls into a tiny ball which just fits a depression under her “chin.”

Once she’s collected enough pollen, she flies to another blossom and checks to make sure that no other moth has been there before. She will not lay eggs on a blossom that has another moth’s eggs in it. When she finds a suitable blossom she punches a hole in the base of the flower near the ovaries and deposits a few eggs. Then she climbs the flower pistil, removes the ball of pollen from under her chin and carefully packs it into a receptacle in the stigma, thereby ensuring that the flower is pollinated and will produce lots of juicy seeds for the moth’s larva.


Yucca Moth Pollinating a Blossom

Moths are careful not to lay too many eggs in one flower. If the moth gets greedy and lays too many eggs in one place the plant drops the pod, thereby losing the seeds but also killing the over-greedy larvae.

When the eggs hatch the larvae feed on the growing seeds. The seeds match the larva’s nutritional needs perfectly, so each larva needs only a few seeds to mature. When the larva is fully developed it chews a little hole in the yucca pod wall, climbs out, and drops to the ground. Then it burrows several inches underground where it goes into the cocoon stage to wait out the winter. When warm temperatures and summer rains arrive, the yuccas begin to bloom again and the pupated yucca moths emerge from underground to start the cycle anew.


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