Cryptobiotic Crust
Wayne's WordIndexNoteworthy PlantsTriviaLemnaceaeBiology 101BotanySearch

   Wildflowers1     Wildflowers2     Wildflowers3     Wildflowers4     Wildflowers5     Chollas1     Chollas2     Anza-Borrego List 

Cryptobiotic Crust
(Anza-Borrego State Park)

© W.P. Armstrong 6 February 2008

  1.    Introduction To Cryptobiotic Crust
  2.    Brown Earthscale Lichen (Placidium)  
  3.    Black Soil Lichen (Collema)
  4.    Blushing Scale Lichen (Psora)
  5.    Xerophytic Desert Liverworts

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.

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.

3. Black Soil Lichen (Collema)

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.

4. 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.

5. 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 (possibly Riccia sp.). The hydrated green thalli have unrolled into their characteristic dorsi-ventrally flattened structure. The orange, scale-like soil lichen is blushing scale lichen (Psora decipiens).

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  

Return To WAYNE'S WORD Home Page
Return To NOTEWORTHY PLANTS Page
Go To Biology GEE WHIZ TRIVIA Page
Go To The LEMNACEAE ON-LINE Page