BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Collema tenax | Black Lichen 



GENERAL BOTANICAL CHARACTERISTICS : 
Collema tenax is a foliose, terricolous lichen with a thick thallus that
is variable in size.  It is usually dark olive green or black in color
[9,32].  Apothecia are small [12].  The photosynthetic symbiont (Nostoc
commune Vauch.) is capable of nitrogen fixation [7].  Collema tenax is
drought and dessication tolerant [1].


RAUNKIAER LIFE FORM : 
NO-ENTRY


REGENERATION PROCESSES : 
Lichen reproduction mainly occurs by means of thallus fragmentation or
the dispersal of isidia and soredia.  Wind, water, or animals play an
important role in the dispersal of these vegetative propagules
[1,15,27].  Collema tenax also produces small apothecia [12,32].


SITE CHARACTERISTICS : 
Lichens, including C. tenax, are very dependent on high relative
humidity, and their abundance is generally in direct relation to the
relative humidity.  Lichens grow best in direct sun.  Since C. tenax is
able to take up moisture from the air, the underlying soil is not as
important a source of moisture as it is to vascular plants.  Lichens can
grow on shallow, sterile soils [2].  Collema tenax is referred to as a
ubiquitous indicator of basic soils [28].  In the Intermountain region,
it is best developed on gypsiferous soils of the Colorado Plateau and on
calcareous soils of the Great Basin [31].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Lichens may be pioneers on some sites because they are dependent on air
moisture rather than soil moisture, and can tolerate shallow
substratums.  They persist in environments too harsh for higher plants,
provided relative humididty is sufficiently high for lichen growth and
temperature is sufficiently low to inhibit competitors [2].  Collema
tenax is often a primary colonizer of disturbed soils [28].  In the Swan
Valley, Montana, it is most often found on disturbed sites [25].

Collema tenax is also abundant in climax grassland and shrub habitats
[17,18,19,20].  It is the most prevalent lichen on both grazed and
ungrazed areas of Canyonlands National Park, Utah [20].  Colema tenax
had the following relative abundance and cover percentage during
successive stages of recovery from grazing (first samples were taken 5
years after grazing pressure had been eliminated [19]:

               Year Sampled        Relative Abundance        Cover (%)
___________________________________________________________________________
Ungrazed           1967                   9710                 19.0
Grazed             1967                   5548                  3.80
Grazed             1977                   4880                  6.65

In Camp Floyd State Park, Utah, C. tenax constituted 3.0 and 6.2 percent
of the cover in areas not grazed for 7 and 20 years, respectively [17].

Cryptogamic soil crusts, including those formed by C. tenax, are common
in seral rabbitbrush communities of the Idaho Snake River Plain.  Their
presence continues through the sagebrush communities that occur in later
succession [27].


SEASONAL DEVELOPMENT : 
NO-ENTRY

Related categories for Species: Collema tenax | Black Lichen