Introduction
Xanthoria (yellow) elegans (elegant) is a bright yellow to orange (with white undersurface) lichen found on both calcareous and siliceous rocks on all continents but Australia[20], sometimes growing over mosses, such as Schistidium apocarpum and Orthotrichum species[22]. It is composed of the fungus (an ascomycota) and a unicellular green alga of the genus Trebouxia[21], and is generally able to survive some of the harshest conditions (see section below).
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Kingdom:
Fungi
Division: Ascomycota Class: Peltigerales Order: Teloschistales Family: Teloschistaceae Genus: Xanthoria Species: X. elegans |
Survivability
X. elegans is regularly found in alpine environments and around the poles[20], and is even widespread on Antartica[23]. In arctic habitats, they must endure harsh periods of low water supply, fluctuating light intensity, and temperature[21]. To cope with dessication, X. elegans enters a state of dormancy when their water content drops below 10-15% of their dry weight, lowering its metabolic activity below detectable levels[21]. Immersion in water or remoistening the lichen immediately triggers a process of reviviscence, with respiration resuming in seconds and photosynthesis within minutes, and hypothesized: rapid repair of cell damage induced by overdrying[21]. It has been launched into space and survived while openly exposed for 18 months[19]. They have also been treated extensively with vacuum conditions and UV radiation in lab, and in general 50% or more spores survive and germinate[18].
Lichenometry
X. elegans was one of the first lichens to be used in lichenometry, the practice of measuring thallus diameter to ascertain the age of an undisturbed rock surface. It has been found to grow at about 0.5mm/yr for during its first century, after which the growth slows down[20].
Right: lichen diameter vs surface age[20]
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References
[18]de Vera, J. P., Horneck, G. G., Rettberg, P. P., & Ott, S. S. (2004). The potential of the lichen symbiosis to cope with the extreme conditions of outer space II: germination capacity of lichen ascospores in response to simulated space conditions. Advances In Space Research, 33(8), 1236-1243. doi:10.1016/j.asr.2003.10.035
[19]http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus/Live_long_and_prosper_i_Xanthoria_elegans_i
[20]McCarthy DP, Smith DJ. (1995). Growth curves for calcium-tolerant lichens in the Canadian Rocky mountains. Arctic and Alpine Research 27 (3): 290–97.
[21]Serge Aubert, Christine Juge, [...], and Richard Bligny (2007). Metabolic processes sustaining the reviviscence of lichen Xanthoria elegans (Link) in high mountain environments. Planta 226(5): 1287-1297.
[22]Martin, L., Suija, A., Schmeimann, M., Leppik, E., & Pykälä, J. (2012). New Estonian records and amendments: Lichenized and lichenicolous fungi. Folia Cryptogamica Estonica, (49), 93-96.
[23]Castello M. (1995). The lichen genus Xanthoria in Antarctica. Cryptogamie Bryologie Lichenologie 16 (2): 79–87.
[19]http://www.esa.int/Our_Activities/Human_Spaceflight/Columbus/Live_long_and_prosper_i_Xanthoria_elegans_i
[20]McCarthy DP, Smith DJ. (1995). Growth curves for calcium-tolerant lichens in the Canadian Rocky mountains. Arctic and Alpine Research 27 (3): 290–97.
[21]Serge Aubert, Christine Juge, [...], and Richard Bligny (2007). Metabolic processes sustaining the reviviscence of lichen Xanthoria elegans (Link) in high mountain environments. Planta 226(5): 1287-1297.
[22]Martin, L., Suija, A., Schmeimann, M., Leppik, E., & Pykälä, J. (2012). New Estonian records and amendments: Lichenized and lichenicolous fungi. Folia Cryptogamica Estonica, (49), 93-96.
[23]Castello M. (1995). The lichen genus Xanthoria in Antarctica. Cryptogamie Bryologie Lichenologie 16 (2): 79–87.