Rusavskia elegans

Rusavskia elegans was first formally described by Johann Heinrich Friedrich Link as Lichen elegans in 1791, ==Description==

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 wide, with lobes less than broad, appressed to loosely appressed. The upper surface is some shade of orange while the lower surface is white, , with short, sparse (an attachment structure produced by some lichens). The vegetative propagules called soredia and isidia are absent, although apothecia are common. 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. The variety R. elegans var. granulifera, characterized by having isidium-like vegetative propagules, has been reported from Greenland and Spitsbergen. ==Growth rate==

Rusavskia elegans was one of the first species used for lichenometry, 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 0.5 mm per year for the first century, before slowing somewhat. ==Habitat and distribution==

This species grows on rock, both calcareous and siliceous, occasionally overgrowing moss or litter. It is often found on exposed to somewhat sheltered sites, often near bird or small-mammal droppings. ==Bioactive compounds==

Various anthraquinone compounds have been identified in R. 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). The algae symbiont produces a cyclopeptide, cyclo-(L-tryptophyl-L-tryptophyl). 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 R. elegans, as in 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. The predominant carotenoid in R. elegans, responsible for the orange-yellow color, is mutatoxanthin. ==References==