Umbilicaria Decussata
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''Umbilicaria decussata'' is a widespread species of
saxicolous This glossary of mycology is a list of definitions of terms and concepts relevant to mycology, the study of fungi. Terms in common with other fields, if repeated here, generally focus on their mycology-specific meaning. Related terms can be found ...
(rock-dwelling)
foliose lichen A foliose lichen is a lichen with flat, leaf-like , which are generally not firmly bonded to the substrate on which it grows. It is one of the three most common growth forms of lichens. It typically has distinct upper and lower surfaces, each o ...
in the family
Umbilicariaceae The Umbilicariaceae are a family of lichenized fungi in the Ascomycota. Species of this family are known from a variety of climates, including temperate, boreal, austral, and warmer montane Montane ecosystems are found on the slopes of moun ...
. It typically grows in high-elevation
alpine Alpine may refer to any mountainous region. It may also refer to: Places Europe * Alps, a European mountain range ** Alpine states, which overlap with the European range Australia * Alpine, New South Wales, a Northern Village * Alpine National P ...
environments.


Taxonomy

It was described as a new species in 1789 by the French botanist and lichenologist
Dominique Villars Dominique Villars or Villar (born 14 November 1745 in Le Villard, part of the commune of Le Noyer, Hautes-Alpes, and died on 26 June 1814 in Strasbourg) was an 18th-century French botanist. His main work is ''Histoire des plantes du Dauphiné' ...
, who placed it in the eponymous genus ''Lichen''. In his original description, Villars characterised the species as a cartilaginous lichen with a black lower surface and brown upper surface, divided into three to five wedge-shaped segments that form a cross-like pattern in the centre. He noted its distinctive transverse wrinkles and reticulated folds formed by the raised epidermis, and observed that fruiting bodies, appearing as large black spots, were rare along the margins. The type locality was given as
granitic rock A granitoid is a broad term referring to a diverse group of coarse-grained igneous rocks that are widely distributed across the globe, covering a significant portion of the Earth's exposed surface and constituting a large part of the continental ...
s in the high
Alps The Alps () are some of the highest and most extensive mountain ranges in Europe, stretching approximately across eight Alpine countries (from west to east): Monaco, France, Switzerland, Italy, Liechtenstein, Germany, Austria and Slovenia. ...
, specifically mentioning the areas of Valgaudemar,
Champoléon Champoléon () is a commune in the Hautes-Alpes department in southeastern France. Population See also *Communes of the Hautes-Alpes department The following is a list of the 162 communes of the Hautes-Alpes department of France ...
, and
Vieux Chaillol The Vieux Chaillol (; ) is a mountain in the Écrins National Park, located in Hautes-Alpes, southeastern France. It has an elevation of 3,163 Meters above sea level and forms a moderate to hard, full day hike from the starting point in the villa ...
. Villars also tentatively linked his species to an earlier illustration by
Johann Jacob Dillenius Johann Jacob Dillen Dillenius (1684 – 2 April 1747) was a German botanist. He is known for his ''Hortus Elthamensis'' ("Eltham Garden") on the rare plants around Eltham, London, and for his ''Historia muscorum'' ("History of Mosses"), a natu ...
, though he expressed uncertainty about this connection. In 1932,
Alexander Zahlbruckner Alexander Zahlbruckner (31 May 1860, Svätý Jur – 1938, Vienna) was an Austrian- Hungarian botanist who specialized in the study of lichens. Johann Babtist Zahlbruckner, an earlier Austrian botanist, was his grandfather. From 1878 to 1883 ...
transferred the
taxon In biology, a taxon (back-formation from ''taxonomy''; : taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular name and ...
to the genus ''
Umbilicaria Rock tripe is the common name for various lichens of the genus ''Umbilicaria'' that grow on rocks. They are widely distributed, including on bare rock in Antarctica, and throughout northern parts of North America such as New England and the Rocky ...
'' to give it the name by which it is now known.


Description

''Umbilicaria decussata'' forms stiff, circular patches (known as
thalli Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
) up to 5 cm across. Each thallus attaches to the rock at a central point on its underside, like an umbrella. The upper surface ranges from light to dark grey and has a distinctive pattern of sharp ridges that radiate outward from the centre, becoming a more net-like pattern of weaker ridges toward the edges. In older parts of the lichen, particularly near the centre, the surface develops a white weathered layer. The underside of the thallus is sooty black due to a dense covering of tiny, dark spores called . These spores are either spherical or egg-shaped and measure about 7 
μm The micrometre (Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a unit of length in the International System ...
across. While these spores typically cover the entire underside in multiple layers, some specimens may have a narrow band around the edge where they are absent, revealing the lichen's natural light grey to brown colouring underneath. Reproductive structures (apothecia) are rarely seen in this species. When present, these appear as small black discs raised on short stalks. This matches Villars's original 1789 description, where he noted that the fruiting bodies appeared as large black spots along the margins and were uncommonly seen. The lichen's
species epithet Specific name may refer to: * in Database management systems, a system-assigned name that is unique within a particular database In Taxonomy (biology), taxonomy, either of these two meanings, each with its own set of rules: * Specific name (botany) ...
''decussata'' refers to the cross-like pattern formed by its ridges, a feature that Villars highlighted in his first description of the species. This pattern, along with its stiff, cartilage-like texture and distinctive colouring (brown-grey above and black below), helps distinguish it from related species.


Habitat and distribution

''Umbilicaria decussata'' is a
cosmopolitan Cosmopolitan may refer to: Internationalism * World citizen, one who eschews traditional geopolitical divisions derived from national citizenship * Cosmopolitanism, the idea that all of humanity belongs to a single moral community * Cosmopolitan ...
lichen species found on all continents, including Antarctica, with a particularly strong presence in high
alpine Alpine may refer to any mountainous region. It may also refer to: Places Europe * Alps, a European mountain range ** Alpine states, which overlap with the European range Australia * Alpine, New South Wales, a Northern Village * Alpine National P ...
environments. It typically grows at elevations between 4,500 and 5,000 metres above sea level, where it colonises
siliceous Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant ...
(
silicon Silicon is a chemical element; it has symbol Si and atomic number 14. It is a hard, brittle crystalline solid with a blue-grey metallic lustre, and is a tetravalent metalloid (sometimes considered a non-metal) and semiconductor. It is a membe ...
-rich) rocks, especially on the vertical faces of large, wind-exposed boulders. Its preference for sites that remain above the winter snowline is characteristic of its ecological niche in these extreme environments. While the species has a global distribution, it shows varying abundance across different mountain ranges. In South America, it can be found along the entire length of the
Andes The Andes ( ), Andes Mountains or Andean Mountain Range (; ) are the List of longest mountain chains on Earth, longest continental mountain range in the world, forming a continuous highland along the western edge of South America. The range ...
mountain chain, from Venezuela in the north to
Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...
in the south, though it is considerably less common in these regions compared to other parts of its range. Its presence in Europe was first documented in the
French Alps The French Alps are the portions of the Alps mountain range that stand within France, located in the Auvergne-Rhône-Alpes and Provence-Alpes-Côte d'Azur regions. While some of the ranges of the French Alps are entirely in France, others, such a ...
, where it was originally discovered growing on granitic rocks in several high-altitude locations. Laboratory studies have shown that ''U. decussata'' show considerable resilience to
photoinhibition Photoinhibition is light-induced reduction in the photosynthetic capacity of a plant, alga, or cyanobacterium. Photosystem II (PSII) is more sensitive to light than the rest of the photosynthetic machinery, and most researchers define the term as ...
(light-induced stress) compared to other Antarctic lichens. When exposed to high-intensity light at low temperatures (5°C), simulating summer conditions in Antarctica, it demonstrated more efficient recovery mechanisms and better photoprotective capabilities than the
fruticose lichen A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or m ...
species '' Usnea antarctica''. This adaptability helps explain its success in exposed, high-altitude habitats where intense light stress is common, particularly during periods when the thallus is hydrated from melting snow or precipitation.


References

{{Taxonbar , from1=Q10709066 , from2=Q59592958 , from3=Q107718506 , from4=Q107477156 decussata Lichen species Lichens described in 1789 Lichens of Asia Lichens of Europe Lichens of North America Lichens of South America Lichens of Subarctic America