ASCOMYCOTA | LECANOROMYCETES > TELOSCHISTALES > Teloschistaceae

Genus Xanthoria, meaning 'golden yellow'

Common name:            Maritime Sunburst Lichen

Synonym:                    -

Habitat:                         Coastal (for this entry)

Substrata:                     Rock

Growth form:                Saxicolous in the context of this page

Thallus:                  Foliose

Apothecia:                    Lecanorine

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

Variable appearance, both in terms of 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.

Xanthoria parietina is a very common and widespread species, occurring on rocks and walls, especially bird-perching sites, such as coastal rocks where gulls rest, or on roofs under aerials, as well as on nutrient-rich trees.

This page features photos taken on the coast. In this environment they are normally a far brighter colour, especially if found on exposed rocks where they get plenty of sunshine. 

It should be noted, that in coastal locations, there could be confusion with Xanthoria calcicola; a not dissimilar species, although normally a deeper orange colour with more contorted, slightly narrower, lobes, which become densely covered in coarse, coralloid, wart-like isidia.