This lichen can be found on stones and rocks , but mostly on the
bark of trees, like the oak on this photo. Here it forms a great
circulaire plaques up to 50cm from side to side.
The the border is foliated, the older center is becoming cracked
with age.
Parmelia saxatilis and pollution
Research done by Batty K.; Bates J.W.; Bell J.N.B. in 2003
showed that this lichen is inhibited by SO2 and NOx air-
pollution. The acidity prevents th reproduction of this
lichen, that became more difficult as the bark of the
oak got older and so more acid.
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