Some similarities to :
Xanthoria Polycarpa, but that lacks the yellow over-lapping wavy sheets.
Golden Shield lichen is a foliose lichen which is often found in exposed sunny places (in shady places, it lacks the conspicuous bright yellow/orange coloration and is instead a light greyish green). It is common on rocks and walls above the splash zone near the sea (hence its other common name 'Shore Lichen'), but also occurs on the bark of deciduous hardwood trees (favouring poplar) well away from the sea. Due to it liking high-levels of nitrogen it is also to be found on farmland and near livestock.
Golden Shield is a bright yellow colour with over-lapping leaf-like lobes and raised elliptical craters which contain the spores and which are a golden orange in colour. Lichens are symbionts between fungii and algae. The greyish green algal part (Chlorococcoid alga) provides the photosynthesis and is protected from the brightness of the sun and UltraViolet radiation by the fungal part which contains a bright yellow pigment called parietin which absorbs UV and blue light. The synthesis of parietin by the green algal symbiont Trebouxia is enhanced by UV-B light and other products of photosynthesis. It accumulates near the surface of the lichen as bright orange crystals, affording protetion from UV light to the algal symbiont. The algal symbiont component usually consists of several differing species of algae from the Genus Trebouxia. Because it is yellow, it was once used to treat jaundice.
Unlike many lichens, Golden Shield is tolerant of atmospheric pollutants such as bisulfite ions or lead and other heavy metals. It is to be found in polluted areas where more sensitive lichens cannot thrive but rather die.
A YELLOW ANTHRAQUINONE
Parietin is an anthraquinone which imparts the golden yellow colour to this and a few other yellow-coloured lichens and is used as a bright yellow pigment. It's name is derived from the specific epithet of the lichen. It protects the lichen from the excesses of UV light when it is at its most vulnerable: when too dry. One of the tests for the Golden Shield lichen is to expose it to potassium hydroxide, KOH, where the bright yellow parietin is transformed into a reddish-magenta compound. Parietin has anti-fungal properties, effective against some powdery mildew fungi. Parietin is also found in the roots of Curled Dock.