On my walk ... the lichen Xanthoria parietina


As the leaves fall from the trees and hedgerow shrubs in autumn other life forms become more apparent, especially lichens. Lichens may not look much; just some crusty, dried up vegetation but they are quite fascinating. A lichen is actually two living organisms, an algae and a fungus, which live together for mutual benefit, it is called symbiosis.

To survive they need a host (or substrate), which may be vegetable or mineral, from which it can derive support and moisture and so they can be found on tree bark, fence posts, bare earth, amongst mosses and grass, on walls and on tombstones. Lichens are not parasitic and do not harm their host and each species has its own preference for substrate on which to grow. 

Identifying lichens can be a real headache and is a somewhat specialised field but there are some common ones that the causal observer like me can recognise and this one is Xanthoria parietina. Its yellow/orange colouring is the clue but it is not the only species coloured like this but most others can be found on mineral substrates whereas this one can be found on both mineral and vegtable and is very common on shrubs, especially blackthorn. Xanthoria parietina is common in towns as it is resistant to air pollution which many species of lichen are not. 

Lichen come with a descriptive terminology of their own which adds to the difficulties in identification and, sadly, very few have common English names. 

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