Xanthoria Aureola
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''Xanthoria aureola'', commonly known as the seaside sunburst lichen, is a lichenized species of fungus in the family
Teloschistaceae The Teloschistaceae are a large family (biology), family of mostly lichen-forming fungi belonging to the class (taxonomy), class Lecanoromycetes in the division (botany), division Ascomycota. The family has a cosmopolitan distribution, althoug ...
and phylum
Ascomycota Ascomycota is a phylum of the kingdom Fungi that, together with the Basidiomycota, forms the subkingdom Dikarya. Its members are commonly known as the sac fungi or ascomycetes. It is the largest phylum of Fungi, with over 64,000 species. The def ...
. ''X. aureola'' can be recognized by its bright yellow-orange pigmentation and abundant strap-shaped .  It is usually found growing on exposed, nutrient-rich rocks in sunny, maritime habitats.  It is largely restricted to European coasts, stretching from Portugal to Norway.


Taxonomy

''Xanthoria aureola'' was first described as ''Parmelia aureola'' in 1809; it was found on seaside rocks in Boshuslän, Sweden and named by
Erik Acharius Erik Acharius (10 October 1757 – 14 August 1819) was a Swedish botanist who pioneered the Taxonomy (biology), taxonomy of lichens and is known as the "father of lichenology". Acharius was famously the last pupil of Carl Linnaeus. Life Ac ...
.  In 1930, Christian Erichsen transferred ''P. aureola'' to the genus '' Xanthoria'' at the species rank, resulting in the accepted binomial ''X. aureola.''  However, from 1965 to 1984, the classification ''X. aureola'' was mistakenly applied to ''X. calcicola'', a closely related species first described in 1937.  Within the genus ''Xanthoria'', DNA sequencing has confirmed that ''X. aureola'' is most closely related to ''X. calcicola'' and more distantly related to ''X. parietina.''  


Habitat and distribution

''Xanthoria aureola'' grows on exposed maritime rocks in sunny areas.  It generally grows on nutrient-rich, siliceous rocks, as well as limestone and lignum.  It is found on European coasts 0–150 meters above sea level.  Some countries in which ''X. aureola'' is commonly found include Spain, Portugal, France, Ireland, Denmark, Sweden, Norway, Italy, and the UK.  It usually grows next to ''X. parietina'', but in greater abundance and on exposed rock. 


Description

The thallus of ''X. aureola'' is bright yellow, orange, or orange-red with a foliose morphology.  It is characterized by overlapping strap-shaped lobes that exhibit dichotomous branching.  When treated with potassium hydroxide, the thallus turns deep red (K+ red).  Average lobe width is 0.46-1.6 mm and average lobe thickness is 135 μm.  ''X. aureola'' has a lower cortex, although no true rhizines.  There are scattered hapters on the cream-colored underside of thick lobes.  The upper cortex is rough with a layer of crystals, dotted with few apothecia.  Chemicals such as parietin, fallacina, emodin, teloistin, and parietinic acid are present, as well as the dominant carotenoid mutatoxanthin.  Mutatoxanthin, a carotenoid important in the protection of the photosynthetic component against harsh sunlight, represents 94.4% of the total carotenoid content in ''X. aureola''.  Of all ''Xanthori''a species, ''X. aureola'' contains the most mutatoxanthin.   ''X. aureola'' is often confused with closely related species ''X. parietina'' and ''X. calcicola''.  In comparison, ''X. aureola'' has a brighter thallus color as well as a considerably thicker medulla (187 mm compared to 114–120 mm).  Additionally, the rough upper surface of ''X. aureola'' contains few apothecia and does not contain soredia or isidia; laminar structures are lobules.  Last, substrate is important: ''X. aureola'' is restricted to seashore rocks, while ''X. calcicola'' and ''X. parietinia'' can be found on almost any rock or wall.    


Ecology

The algal symbiont in ''X. aureola'' is ''
Trebouxia ''Trebouxia'' is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions.Erokhina, L. G., Shatilovich, A. V., Kaminskaya, O. P., & Gilichinskii, D. A. (2004 ...
''.  ''Trebouxia'' fixes 14C mainly into ribitol during photosynthesis; approximately 80% is ribitol, 5% is sucrose, 4% is organic acids, and 9% is baseline CH.  Therefore, ribitol is the main way in which carbohydrates are transferred among symbionts in the thallus.  The flow of carbon from ''Trebouxia'' to the fungus is efficient, with a steady rate of 15 minutes.  Little carbon (~2%) is stored as insoluble compounds in the thallus.  The mean chlorophyll content per algal cell is 3.0-4.8 x 10−6 mg.   Environmental disturbance plays an important role in efficiency and productivity.  Lichen species are often used to monitor pollution since they are sensitive to SO2, heavy metals, salt, and high levels of UV.  Environmental stress (i.e., increased UV light) enhances the creation of reactive oxygen species (ROS), including superoxide and hydrogen peroxide.  The formation of ROS was higher in all treatments with greater UV, although ''Xanthoria'' species showed the greatest resilience under harsh light conditions.  Additionally, pre-treatment with salicylic acid coupled with high-energy radiation resulted in fewer amino acids, notably Glu, Tyr, and Pro.  Amino acids are essential in the formation of proteins and basic biochemical functions.  Another experiment underscored the sensitivity of ''X. aureola'' to high concentrations of heavy metals and salt.  Membrane integrity was measured via conductivity and potential photosystem II (PSII) efficiency (Fv/Fm), with the former being a more accurate measure.  High UV, salt, and heavy metal concentrations increased membrane dissolution and electrolyte leakage.  ''X. aureola'' was more resistant to salt than other lichenized species ''Lobaria pulmonaria'' and ''Parmelia sulcata''.  Copper and zinc had no effect on Fv/Fm of ''X. aureola''.  It is likely that zinc and iodine in seawater protect ''Trebouxia'' and increase resistance to high salt and UV.  Increasing environmental stress may exacerbate ROS formation and electrolyte leakage.  


References

{{Taxonbar, from=Q10721825 Teloschistales Lichens described in 1810 Lichen species Lichens of Europe Taxa named by Erik Acharius