Rusavskia elegans (formerly Xanthoria elegans), commonly known as the elegant sunburst lichen,[1] is a lichenized species of fungus in the genus Rusavskia, family Teloschistaceae. Recognized by its bright orange or red pigmentation, this species grows on rocks, often near bird or rodent perches. It has a circumpolar and alpine distribution. It was one of the first lichens to be used for the rock-face dating method known as lichenometry.
Quick Facts Scientific classification, Binomial name ...
The thallus of this lichen is described as foliose, having the aspect of leaves, although the central portions of the thallus may appear nearly crustose. It is small, typically less than 5cm (2in) wide, with lobes less than 2mm (0.08in) broad, appressed to loosely appressed. The upper surface is some shade of orange while the lower surface is white, corticate, with short, sparse hapters (an attachment structure produced by some lichens). The vegetative propagules called soredia and isidia are absent, although apothecia are common.[9] It has been described as possessing swollen, orange-yellow thalli (in streams), compact orange thalli (on boulders) or dark orange-red thalli on the driest rock faces.[10]
Herbarium specimen of R.elegans, showing the lobes at 40XmagnificationR.elegans on the rock's surfaceR.elegans on rocky islet in Gaspereau Lake
Growth rate
Rusavskia elegans was one of the first species used for lichenometry,[12] a technique of estimating the age of rock faces by measuring the diameter of the lichen thalli growing on them. After an initial period of one or two decades to establish growth (the ecesis interval), R.elegans grows at a rate of 0.5mmperyear for the first century, before slowing down somewhat.[13][14]
Habitat and distribution
This species grows on rock, both calcareous and siliceous, occasionally overgrowing moss or litter or rock. It is often found on exposed to somewhat sheltered sites, often near bird or small-mammal droppings.[9] It has also adapted successfully to growth on man-made and natural growing surfaces from the sea-water spray zone to the boreal forest and in the grasslands of the continental interior.[15][16][17] It can thrive in areas having less than 6 centimetres (2.4in) annual precipitation and can survive submerged in streams for much of the growing season.[10]
Rusavskia elegans has an extremely broad circumpolar and alpine distribution, and is found on all continents except Australia.[18] It is widespread in Antarctic regions.[19]
The 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 16hours of vacuum at 10−3Pa and UV radiation at wavelengths less than 160nm or greater than 400nm.[20]R.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.[21]
Bioactive compounds
Various anthraquinone compounds have been identified in R.elegans, including allacinal, physcion, teloschistin,[22] xanthorin,[23] and erythoglaucin,[24] murolic acid and a glycoside derivative of murolic acid ((18R)-18-O-β-D-apiofuranosyl-(1-2)-β-D-glucopyranoside).[25] The algae symbioant produces a cyclopeptide, cyclo-(L-tryptophyl-L-tryptophyl).[8]
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.[26] In R.elegans, like many Rusavskia 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 R.elegans in Antarctica.[27] The predominant carotenoid in R.elegans, responsible for the orange-yellow color, is mutatoxanthin.[26]
Fedorenko, Natalya M.; Stenroos, Soili; Thell, Arne; Kärnefelt, Ingvar; Kondratyuk, Sergey Y. (2009). "A phylogenetic analysis of xanthorioid lichens (Teloschistaceae, Ascomycota) based on ITS and mtSSU sequences". In Thell, Arne; Seaward, Mark; Feuerer, Tassilo (eds.). Diversity of Lichenology – Anniversary Volume. Bibliotheca Lichenologica. Vol.100. J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung. pp.49–84. ISBN978-3-443-58079-7.
Fedorenko, Natalya M.; Stenroos, Soili; Thell, Arne; Kärnefelt, Ingvar; Elix, John A.; Hur, Jae-Seoun; Kondratyuk, Sergij Y. (2012). "Molecular phylogeny of xanthorioid lichens (Teloschistaceae, Ascomycota), with notes on their morphology". In Kärnefelt, Ingvar; Seaward, Mark R.D.; Thell, Arne (eds.). Systematics, biodiversity and ecology of lichens. Bibliotheca Lichenologica. Vol.108. pp.45–64. ISBN978-3-443-58087-2.
Fahselt D, Krol M (1989). "Biochemical comparisons of two ecologically distinctive forms of Xantharia elegans in the Canadian High Arctic". The Lichenologist. 21 (2): 135–45. doi:10.1017/S0024282989000253. S2CID86595226.
Giralt M, Nimis PL, Poelt J (1993). "Studies on some species of the lichen genus Xanthoria with isidia-like vegetative propagules". Journal of the Hattori Botanical Laboratory. 74: 271–85.
Hinds JW. (1995). "Marine influence on the distribution of Xanthoria parietina, X. elegans, and X. ulophyllodes on marble gravestones in Maine". Bryologist. 98 (3): 402–10. doi:10.2307/3243380. JSTOR3243380.
de Vera JP, Horneck G, Rettberg P, Ott 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): 1236–43. Bibcode:2004AdSpR..33.1236D. doi:10.1016/j.asr.2003.10.035. PMID15806704.
