This photo is an example according to Tristan Gooley’s latest book of the most underrated and underrappreciated groups in nature. Carl Linnaeus called them (from a Latin translation) ‘Poor little peasants of nature’. The Greeks; eruptions, warts or leprosy.
Here we have Xanthoria polycarpa (I think) which is sensitive to light levels, preferring south facing surfaces; it acts as a colour compass. It can also gauge timescales referred to as ‘lichenometry’. (See section on lichens in The Walkers Guide to Outdoor Clues and signs). This specimen was found at school. The FSC guide says it’s nitrogen and acid tolerant. Amazing!
