lichen is used as a model system to study the potential to resist extreme environments of outer space. Out of various lichens tested, it showed the ability to recover from space-simulating situations, including exposure to 16 hours of vacuum at 10−3 Pa and UV radiation at wavelengths less than 160 nm or greater than 400 nm. X. elegans has survived an 18-month exposure to solar UV radiation, cosmic rays, vacuum and varying temperatures in an experiment performed by the ESA outside of the ISS. Bioactive compounds Various anthraquinone compounds have been identified in X. elegans, including allacinal, physcion, teloschistin, xanthorin, and erythoglaucin, murolic acid and a glycoside derivative of murolic acid ((18R)-18-O-β-D-apiofuranosyl-(1-2)-β-D-glucopyranoside). Carotenoids Carotenoids have a number of physiological functions in lichens, such as enhancing the availability of light energy for photosynthesis, and protecting the organism from the photooxidizing action of UV light. In X. elegans, like many Xanthoria species, specimens growing in areas with intense UV radiation contain more carotenoids than those grown in more shaded areas. The biosynthesis of carotenoids is also dependent on the season of the year, as was shown in a study of X. elegans in Antarctica. The predominant carotenoid in X. elegans, responsible for the orange-yellow color, is mutatoxanthin. See also Xanthoria parietina (common orange lichen) References Teloschistales Lichen species Lichens of Europe Lichens of Africa Lichens of Asia Lichens of North America Lichens described in 1803 Taxa named by Johann Heinrich Friedrich Link