User:Chris794109740/sandbox



An endolithic lichen is a crustose lichen that grows inside solid rock, growing between the grains, with only the fruiting bodies exposed to the air. An example is Caloplaca luteominea subspecies bolandri. Its name derives from the word endolith which is an organism that lives inside rocks, and lichen which are a species made up of a combination of alga and fungus. This lichen can be found in many environments but thrives in the most extreme climates. They are known to greatly influence weathering in the rocks they inhabit, whereas other species of lichen can protect rocks.

==Anatomy of Verrucaria rubrocinta == The species Verrucaria rubrocincta, commonly found on caliche from desert pavements of the northern Sonoran Desert produces a micrite layer made of mostly fine grained calcite at the surface of the rock it is living in. Below this micrite it has an algal layer, Fruiting bodies can be seen protruding through the algal and micrite layers. Under these layers are Pseudomedulla layers; the Pseudomedulla layers have a composition of semi disintegrated caliche, along with the Ca oxalates weddellite and whewlite, and detrital minerals. This species of lichen also has sparse hyphae becoming less numerous with greater depth below the rock surface. The depth of the hyphal penetration is dependent on the integrity of the caliche as well as the age of the thallus. This lichen is characterized by a dotted pattern of rounded patches made up of the lichens fruiting bodies extruding through the surface of the rock.

Nutrition
Lichens are a mutual symbiosis of a fungus (mycobiont) and alga and/or cyanobacterium (photobiont). The algal or cyanobacterial portion is photosynthetic, so it uses sunlight, water, and CO2 to produce sustenance for itself. Lichens have no specific organs for water conservation and control over moisture content. They increase the porosity of the rocks they grow in through bio-deterioration to increase water availability and absorption, which aids in photosynthesis.

Habitat
Endolithic lichens thrive in extreme environments because other competing species cannot survive there. In more habitable environments they are out competed and usually dominated by other species of lichens. Although they live in the most extreme environments, an increase in moisture does help increase their growth. Some examples of places endolithic lichen are known to live and thrive are the dry valleys of southern Victoria Land Antarctica, the clarens sandstone in the karoo basin of southern Africa, and throughout Norway. They have the ability to survive in such harsh climates because they grow predominantly inside of rocks with only their fruiting bodies exposed to the environment, whereas other species such as epilithic lichen grow outside the rock leaving them exposed to the elements. Although endolithic lichens grow in a number of different rock types they are most common in rocks that reduce the effect of high light intensities. It is these rocks that are the least habitable for the competing species of lichen that require more light for their photosynthetic processes than endolithic lichen do.

Survival strategy
Endolithic lichens are known as extremophiles. They are called this because they thrive in extreme environments characterized by rapid fluctuations from high to low temperature as well as high rates of water evaporation, and extreme dry periods. They thrive in these locations because there is not much competition from other life forms. They are able to survive in arid and cold periglacial environments because they exist among internal discontinuities and along planes of weakness of rocks which protect them from harsh climates. Maximum thallus hydration in endolithic lichens is reached at levels five times lower than in epilithic lichens giving them the ability to live in much dryer environments. Endolithic lichens are slow growing, with certain species having a radial growth rate of about 2.1 mm per year. When found in less extreme environments it is common to see them overgrown by epilithic species of lichens.

Weathering
The exact rates and processes of weathering caused by endolithic lichens are not well known because there have only been minimal studies done on the subject. Some species of lichens are known to protect rock surfaces from weathering, while endolithic lichens tend to weather rock surfaces exceptionally fast. In the clarens sandstone in southern Africa, the colonization of lichens in the endolithic environment was observed to remove cementing material and replace it with more voluminous algal cells and fungal hyphae. The added volume from the algal cells and fungal hyphae increases the inter crystal space and causes an overall expansion of the sandstone colonized by the lichen. In the lichen’s medullary and cortical layers, there is a reduced cohesion of quartz grains as a result of colonization. This reduced cohesion, along with the other previously mentioned sandstone-lichen-thallus qualities, results in a rearrangement of quartz crystals, correlated with increased strain and mechanical weathering. Humidity and temperature of the rock and air surrounding the lichen are thought to have a direct connection to thallus strain: an increase in temperature increases the physical strain, while high air humidity increases the difference in physical strain between the rim and thallus. The increased humidity also causes an increase in water absorption by mycobiont hyphae and photobiont cells, which causes them to swell, thus increasing volume and the amount of weathering. It is thought that the species lecidea auriculata can penetrate the claren sandstones at an annual rate of 0.1 mm. In severe periglacial environments endolithic lichens are the primary source of weathering, particularly due to a lack of moisture which prevents the occurrence of other biological, chemical, and physical weathering. In the desert caliche inhabited by V. rubrocinta; the colonization of the lichen causes the rock to flake off along the margins of the thallus. However, the formation of a surface layer of micrite is directly associated with the growth of the lichen. The micrite is not present on areas of caliche uninhabited by the lichen.