ASCOMYCOTA | LECANOROMYCETES > TELOSCHISTALES > Teloschistaceae

Genus Xanthoria, meaning 'golden yellow'

Common name:            Sunburst Lichen       

Synonym:                    -

Habitat:                         Montane (for this entry)

Substrata:                     Bark, worked wood

Growth form:                Corticolous and lignicolous in the context of this page

Thallus:                  Foliose

Apothecia:                    Lecanorine

BLS identity rating:        Graded 1/5 (identification should be straightforward)

Variable appearance, both colour and form, dependent on habitat and exposure to the sun, hence the three entries - montane, woodland and coastal.

Thallus forming neat individual rosettes, typically between 5-15cm dia., or, occasionally, more extensive patches that may create small colonies; thallus composed of loosely adpressed flat or wrinkled, smooth lobes, up to 7mm wide especially at the margin of the thallus where they widen, the precise form of the lobes varies slightly between specimens in exposed coastal locations where they may be shorter and more tightly applied to rock, to those in less exposed woodland sites for example where the lobes may be slightly longer and looser; with larger, older specimens it is very common for the centre of the thallus to break up; colour also varies from bright yellow-orange or gold-orange in sunny locations, to greenish-yellow or greenish-grey in shaded situations, such as in woodland; apothecia are usually numerous, sessile, from 2-5mm dia., disc flat to concave, orange to yellow-orange if exposed to the sun, or greenish in less exposed locations, with either a pale or concolourous thalline margin.

The variation in colour is due to the chemical xanthorin, which is thought to be produced as a defence against UV radiation and, consequently, is far more evident when the lichen is fully exposed to the sun, such as on coastal rocks, cement tiled roofs or exposed tree branches. When it is growing in the shade, it does not require the same level of protection, so the xanthorin isn't produced and the lichen remains greenish-grey. In, or after, rain it appears more greenish-yellow as the algae is more visible through the more translucent fungus.

Whilst the other entries for this species photographed in Britain in woodland and on the coast confirm that Xanthoria parietina occurs widely on both trees and rocks, as well as roofs, in Austria, where these montane specimens were found, it is regarded as a mainly epiphytic species, most likely to be seen growing on bark and wood rather than on rocks. It is widespread in the Alps up to the subalpine belt especially in open, taiga-like forests dominated by European Larch [Larix decidua] and/or Swiss Pine [Pinus cembra].