Cryptobiotic Crust
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Cryptobiotic Crust
(In Anza-Borrego Desert State Park)

© W.P. Armstrong 20 April 2012

  1.    Introduction To Cryptobiotic Crust
  2.    Brown Earthscale Lichen (Placidium)  
  3.    Black Soil Lichen (Collema)
  4.    Collema In Twin Oaks Valley?
  5.    Blushing Scale Lichen (Psora)
  6.    Rock Olive Lichen (Peltula)
  7.    Squamulose Cladonia Soil Crust
  8.    Xerophytic Desert Liverworts
  9.    Xerophytic Moss In Mojave Desert
 10.   References About Lichens
Cryptobiotic Crust On Other Pages:
     The RareTexosporium sancti-jacobi
     Cryptobiotic Crust On Emerald Heights
     Liverworts & Lichens On Owens Peak

1. Introduction

The dark crust is mostly the soil lichens of the genera Placidium and Collema.

Arid desert regions throughout the world where vegetation is sparse sometimes develop specialized communities of cyanobacteria, mosses and lichens. The surface soil is held together by these associations called "cryptobiotic soil crusts." These crusts are very fragile and are easily damaged by walking on them. In Anza-Borrego Desert, two of the components of this association include the soil lichens Placidium lacinulatum and Psora decipiens. The desiccated scale-like squamules of Placidium are dark brown most of the year. After sufficient rains, the thallus turns greenish. Another genus of soil lichens commonly associated with cryptobiotic crusts is Collema. They are called jelly lichens because the thallus becomes gelatinous when it imbibes water after rains.

Cryptobiotic crusts are very beneficial because they hold soils in place and protect the underlying sediments from erosion. They are also an important pioneer stage in succession on bare ground (xerarch succession), thus enabling grasses and herbs to become established.

Note: Desert pavement is a completely different nonbiological phenomenon. The flattened surface is covered by small pebble-sized rocks. There are several hypotheses to explain this phenomenon, including the removal of fine sand particles around the rocks by the wind.

Desert pavement in Anza Borrego Desert State Park. The cacti include flowering fish-hook cactus (Mammilara dioica) in the foreground and hedgehog cactus (Echinocereus engelmannii).

2. Brown Earthscale Lichen (Placidium lacinulatum)

  How Large Is Penny In The Above Image  

Placidium lacinulatum, a squamulose soil lichen commonly associated with cryptobiotic crust in Anza-Borrego Desert State Park. The thallus is composed of small, brown, scalelike squamules. The spore-bearing perithecia are embedded in the thallus.

Center: The black, granular, tarlike area is an isidiate, cyanolichen of the genus Collema (possibly C. coccophorum). It is surrounded by the brown, scalelike squamules of Placidium lacinulatum. In Placidium, the spore-bearing perithecia are embedded in the thallus (blue arrow). Magnification 10x.

Green algal cells inside the thallus of Placidium. The photobiont is a species of Myrmecia (Chlorophyta). The similar-appearing Peltula has unicellular cyanobacteria for its photobiont. Magnification 400x.

3. Black Soil Lichen (Collema)

Black cryptobiotic soil lichen, mostly Collema (possibly C. coccophorum).

Minute globular lobes (isidia) and minute apothecia of black soil lichen (Collema) in between the light brown squamules of earthscale (Placidium). The isidiate thallus of Collema imbibes water and becomes gelatinous.

Center: The black, granular, tarlike area is an isidiate, cyanolichen of the genus Collema (possibly C. coccophorum). It is surrounded by the brown, scalelike squamules of Placidium lacinulatum. In Placidium, the spore-bearing perithecia are embedded in the thallus (blue arrow). Magnification 10x.

Magnified view of black soil lichen of the genus Collema showing apothecium (red arrow) and abundant spherical isidia. Magnification 30x.

Close-up view of apothecium (red arrow) of black soil lichen of the genus Collema (possibly C. coccophorum). The minute, lecanorine apothecium (margin same color as thallus) is about 0.6 mm in diameter. The thallus is composed of numerous, minute globular lobes (isidia) that imbibe water and become gelatinous and greenish-black. Magnification 60x.

Magnified view of a black soil lichen of the genus Collema showing a portion of the hymenial layer from an apothecium and scattered filaments of a cyanobacterium (presumably Nostoc). The Nostoc filaments fragment into numerous individual cells under the cover slip. Some filaments show the cellular sheath typical of cyanobacteria. Magnification 600x.

A Disclaimer On The
Identification of Collema:

The left image shows an ascus from the above apothecium that contains 8 colorless ascospores. Spores of Collema are typically septate. Perhaps these spores are immature. Some of them may have a faint septum. Magnification 1000x.

  More Images Of Cyanobacteria  

4. Possible Collema In Twin Oaks Valley San Diego County
On Dry, Hard Las Posas Clay Along Bridle Path Near My Home

The photobiont appears to be the cyanobacterium Scytonema rather than Nostoc. I am reasonably certain the 2-celled spores are from Collema; however, I was unable to find a well-defined hymenial layer and asci. The greenish tinge is probably due to lighting with compound microscpe.

San Marcos Gabbro, a dark, granite-like, bedrock behind my home that contains iron & weathers into reddish Las Posas Clay. Runoff water from recent heavy rains of April 2020 colored my concrete driveway! Some rare wildflowers in San Diego County are endemic to this soil, including the beautiful San Diego Thornmint in Emerald Heights above my home.

  See Wildflowers & Cryptobiotic Crust In Emerald Heights  

5. Blushing Scale Lichen (Psora decipiens)

Psora decipiens, a squamulose soil lichen associated with cryptobiotic crust in Anza-Borrego Desert State Park. The thallus is composed of orange-brown, scalelike squamules. Individual squamules develop a white margin with several black apothecia. The smaller, darker brown squamulose lichen is Placidium lacinulatum, another indicator of cryptobiotic crust. The black areas to the upper left of penny is yet another minute soil lichen of the genus Collema.

  How Large Is Penny In The Above Image  

Close-up view of a scalelike squamules of Psora decipiens showing white margin and several black apothecia. The smaller, darker brown squamulose lichen is Placidium lacinulatum, another indicator of cryptobiotic crust.

Reddish-orange squamules of the widespread soil lichen called "blushing scale" (Psora decipiens). Psora has conspicuous, black, mound-shaped apothecia on the upper side of its thallus.

This chunk of clay supports two similar-appearing genera of brown squamulose soil lichens: Placidium and Psora. The Placidium is similar to P. lacinulatum). The Psora resembles P. globifera. Although both genera have a thallus composed of brown, scale-like lobes (squamules), their spore-bearing bodies (ascocarps) are quite different. The squamules of Placidium have spore-bearing perithecia embedded in the thallus. Each perithecium has a small circular opening on the upper side of the thallus. Squamules of Psora have one or several globose apothecia on the upper side, appearing like dark, dome-shaped bodies.

Magnified view of two species of squamulose lichens crowded together on the gabbro clay substrate. Although the squamules are similar, their reproductive (spore-bearing) bodies (ascocarps) are very different. Placidium has flask-shaped perithecia embedded in the thallus. Each perithecium has a small circular pore on the upper side of the thallus. Psora has conspicuous, dark, mound-shaped apothecia on the upper side of its thallus. This may be a different species of Psora, possibly P. globifera or P. californica. Magnification 10x.

  List Of Lichen Species Featured On Wayne's Word   

6. Desert Rock Olive (Peltula obscurans)

While walking along the alluvial slope west of the Anza-Borrego State Park Visitor Center, I noticed a black cryptobiotic soil lichen in the ravines. I thought it was the usual species (Collema or Placidium), but to my surprise it was a different genus (Peltula). This species has a squamulate thallus composed of scalelike sections called squamules. In the center of some squamules is a sunken apothecium. The thallus of Placidum is similar, except the squamules contain multiple embeddded perithecia, each with a minute opening (pore). Unlike the green alga photobiont in Placidium, the photobiont in Peltula is a cyanobacterium. The other common, dark cryptobiotic lichen in Anza-Borrego (Collema) also has symbiotic cyanobacteria.

Although the squamules appear similar, Peltula is very different from Placidium


Anacystis?
 According to Lichen Flora of the Greater Sonoran Desert Region (Volume 1) by Tom Nash III, et al. (2002), the primary photobiont of Peltula is the unicellar cyanobacterium Chroococcidiopsis or Myxosarcina. In Lichens of North America by I.M. Brodo, S.D. Sharnoff and S. Sharnoff (2001), the cyanobacterial photobiont is listed as Anacystis. Chroococcidiopsis is described as coccoidal in most references; however, the bacterial cells I observed inside Peltula were oval. Each cell was surrounded by a transparent sheath that appeared like a thin, white border. On a microscope slide under under 1,000X magnification there were numerous oval cells with a faint blue-green color. I did not see the green algal cells of Placidium or the nostoc-like filaments of cyanobacteria found in Collema.

Highly magnified view of cyanobacteria inside Peltula squamule using oil immersion and 1,000x magnification. The oval cells are approximately 3.0 µm long and 1.0 µm wide. Their shape resembles images of Anacystis on the Internet. The transparent cellular sheath appears like a thin white border. These bacterial cells are smaller than human red blood cells (7.5 µm in diameter).

Chroococcidiopsis is one of the most primitive cyanobacteria (blue-green algae) known. It is a photosynthetic bacteria known for its ability to survive harsh environmental conditions, including both high and low temperatures, desiccation, ionizing radiation, and high salinity. It is known as an extremophile and it is one of the species NASA is studying for possible farming in greenhouses on Mars. The colonies could provide oxygen and fresh food for astronauts. Perhaps genes from these bacteria could be introduced into other plants, thus making them resistant to environmental extremes.

Cryptobiotic soil lichen (Peltula), possibly P. obscurans var. hassei. Some squamules appear pubescent with minute silvery hairs. These may be fungal hyphae, possibly a mold. The lichen thallus varies from dark olive to reddish-brown, depending its moisture content.

  List Of Lichen Species Featured On Wayne's Word   
More Soil Lichens Forming Cryptobiotic Crust
Lichen Crust Terminology & Desert Varnish

7. Squamulose Cladonia Forming Dry Soil Crust

Athough the genus Cladonia includes many species in wet areas of the Pacific Northwest, there are several species that form soil crusts in dry areas of the western North America. This genus is characterized by an upright structure called a podetium that is truly a lichen characteristic not present in unlichenized fungi. It is a good example of the synergism between the algal and fungal symbionts of lichens.

Cladonia forming a soil crust in San Diego County. This is may be C. fimbriata or C. pyxidata, although C. chlorophaea is very similar. Rosentreter, Bowker, and Belnap (2007) include C. fimbriata in their A Field Guide to Biological Soil Crusts of Western U.S. Drylands.

8. Xerophytic Desert Liverworts

Several genera of liverworts are associated with cryptobiotic crust in the Mojave and Colorado Deserts of California, including Asterella, Mannia, Riccia and Targionia. During prolonged periods of desiccation, the thallus of these species rolls up into a slender, tight cylinder exposing the black or intensely pigmented ventral surface. Thus, the dorsal photosynthetic surface is well protected from the sun. In Borrego Palm Canyon, Anza-Borrego State Park, the rolled-up thalli appear like slender black threads on the soil surface. They imbibe water after a rain and quickly unroll and swell into green, dorsi-ventrally flattened thalli typical of thallose liverworts.

  Adaptations Of Bryophytes In The Near & Middle East  

The slender, black threads with dichotomous branching are the rolled-up, desiccated thalli of a liverwort (probably Riccia). The brown, scale-like soil lichen is brown earthscale lichen (Placidium lacinulatum).

The rolled-up, desiccated thalli of a liverwort (probably Riccia).

The slender, black threads with dichotomous branching are the rolled-up, desiccated thalli of a liverwort. The hydrated green thalli have unrolled into their characteristic dorsi-ventrally flattened structure. The brown, scale-like soil lichen is brown earthscale lichen (Placidium lacinulatum).

Close-up view of the desiccated and unrolled (hydrated) thalli of a liverwort.

  More Images Of Terrestrial & Aquatic Liverworts  
Moss Fertilization By Microscopic Springtails

9. Xerophytic Moss In The Mojave Desert
How a Remakable Moss Keeps Cool in the Mojave Desert

PLOS ONE: "Life Under Quartz: Hypolithic Mosses in the Mojave Desert"
by Jenna T. B. Ekwealor & Kirsten M. Fisher 22 July 2020
doi.org/10.1371/journal.pone.0235928

Jenna Ekwealor and Kirsten Fisher found the green moss (Syntrichia caninervis) sheltered under translucent quartz stones, shielding the moss from heat, cold, drought and intense ultraviolet rays. The Mojave Desert can be extremely hot during the summer months and very cold in winter, especially at night. Under a canopy of translucent quartz stones the moss is kept cooler during the summer and warmer in winter. The stones also trap moisture under them, keeping the plants moist. Sheltered mosses grew much faster and taller than the ones left out on exposed soil without protection. The quartz stones needed to be just the right size, around an inch thick and translucent enough to act like a greenhouse window, letting up to 4% of incident light to pass through but blocking out harsh ultraviolet light that could harm the moss.

The ubiquitous desert lichen Syntrichia caninervis in its dormant phase on parched desert soil. [Note: This is a public domain image available from Wikipedia.] The dark color may work like sun screen to filter out harmful UV radiation. When growing under protective quartz or in a greenhouse, the moss assumes its green coloration. This moss has an enormous distribution throughout dry areas of North America and Eurasia. It has been studied extensively by bryologists. Although it is dioecious with separate male and female plants, male plants are not common and sporophytes are very rare. I'm quite certain I have walked over miles of these remarkable little mosses without ever stopping to photograph them. The article by Ekwealor & Fisher mentions a Sheep Canyon study site near Wrightwood, California. My parents had a nearby mountain cabin that unfortunately was destroyed in a wild fire that swept through this area in the 1950s.

Quartz is a hard crystalline mineral composed of silicon dioxide. It is second only to feldspar as the most abundant minerals in the Earth's crust. It is common in igneous, metamorphic and sedimentary rocks throughout mountain and desert regions of the world. The following image shows the translucent quality of a quartz fragment compared with a U.S. Penny.

10. References

  1. Ahmadjian, V. 1967. The Lichen Symbiosis. Blaisdell Publishing Co., Waltham, Massachusetts.

  2. Armstrong, W.P. 2002. "The Marriage Between Algae and Fungi." Wildflower 18 (1): 10-16.

  3. Armstrong, W.P. and J.L. Platt 1993. "The Marriage Between Algae and Fungi." Fremontia 22 (2): 3-12.

  4. Atsatt, P.R. 1988. "Are Vascular Plants Inside Out Lichens?" Ecology: 69 (1): 17-23.

  5. Atsatt, P.R. 2003. "Fungus Propagules in Plastids: The Mycosome Hypothesis." International Microbiology 6: 17-26.

  6. Brock, T.M. and M.T. Madigan. 1988. Biology of Microorganisms (5th Edition). Prentice Hall, Englewood Cliffs, New Jersey.

  7. Brodo, I.M., Sharnoff, S.D. and S. Sharnoff. 2001. Lichens of North America. Yale University Press, New Haven and London.

  8. Dobson, F. 1979. Lichens: An Illustrated Guide. The Richmond Publishing Co. Ltd., Richmond, Surrey, England.

  9. Dorn, R.I. 1982. "Enigma of the Desert." Environment Southwest Number 497: 3-5.

  10. Dorn, R.I. and T.M. Oberlander. 1982. "Rock Varnish." Progress In Physical Geography 6: 317-367.

  11. Dorn, R.I. and T.M. Oberlander. 1981. "Microbial Origin of Desert Varnish." Science 213: 1245-1247.

  12. Ekwealor, J. B., and K.M. Fisher. 2020. "Life Under Quartz: Hypolithic Mosses in the Mojave Desert" PLOS ONE: doi.org/10.1371/journal.pone.0235928.

  13. Hale, M.E. and M. Cole. 1988. Lichens of California. University of California Press, Berkeley.

  14. Hale, M.E. 1969. How to Know the Lichens. Wm. C. Brown Company, Dubuque, Iowa.

  15. McCune, B. and T.Goward. 1995. Macrolichens of the Northern Rocky Mountains. Mad River Press, Inc., Eureka, California.

  16. Nash, T.H. III, Ryan, B.D., Gries, C. and F. Bungartz. 2002, 2004, 2007. Lichen Flora of the Greater Sonoran Desert Region Volumes I., II. & III. Lichens Unlimited, Arizona State University, Tempe, Arizona.

  17. Nash, T.H. III. 1996. Lichen Biology. Cambridge University Press, Cambridge.

  18. Purvis, W. 2000. Lichens. Smithsonian Institution Press, Washington, D.C.

  19. Retallack, G. 1994. "Were the Ediacaran Fossils Lichens?" Paleobiology 20 (4): 523-544.

  20. Richardson, David H.S. 1974. The Vanishing Lichens. Hafner Press, New York.

  21. Rosentreter, R., Bowker, M., and J. Belnap. 2007. A Field Guide to Biological Soil Crusts of Western U.S. Drylands. U.S. Government Printing Office, Denver, Colorado. This excellent guide to cryptobiotic crusts is available on-line at: http://sbsc.wr.usgs.gov/products/pdfs/Field_Guide_Book_25.pdf

  22. Vitt, D.H., Marsh, J.E. and R.B. Bovey. 1988. Mosses, Lichens & Ferns of Northwest North America. Lone Pine Publishing, Edmonton, Alberta, Canada.

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