A common but colourful lichen

March 14th 2019

Helen Lockhart took a photograph of this lovely orange lichen on her smartphone on 20th January 2018 and later showed it to me.  It was on the roadside wall of the old burial ground at Stoer (NC0428).

The species is Xanthoria parietina, once known as Yellow Crotal.  It was gathered, in the past, to produce dyes in a wide range of colours, both browns and in the pink/purple/blue range.

Although one of the commonest leafy (foliose) lichens in the British Isles, it is amongst the most colourful and worth a second look.  It is unusually resistant to sulphur dioxide pollution and has a positive preference for nutrient-rich sites with high nitrogen levels, such as bird perches.  Away from these, it occurs commonly in coastal areas and also inland on trees like elder which have alkaline bark.  

In shady sites, the orange pigment may not develop and an underlying grey-green colour shows through.  Occasionally, as here, the thallus is multicoloured even in plants in full sun.  The large flat-topped fruiting bodies, or apothecia, show well in this photograph. They generate the spores of the fungus in the symbiotic partnership with an alga or cyanobacterium which constitutes a lichen. 

Ian M. Evans

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