Lichen grows on a column outside a 'Grecian Temple' - a folly, in the grounds of the grand English Palladian mansion "Stourhead".
Lichens are tolerant of a wide range of ecological conditions, but, perhaps surprisingly, very sensitive to atmospheric pollution. Lichens are actually a fungi that has evolved to live symbiotically with a partner that photosynthesises. Perhaps an algae or a bacterium, and sometimes both. This partnership is very delicate, and easily broken and so lichens are sometimes used by scientists as biomonitors of environmental health. And as bioindicators of environmental change.
So, where you see lichen growing well, you can be pleased that the air is very clean.
I like the surprising colours and shapes, and the crinkled textures. They please me that they tenaciously cling on in such dry, hot and bright places. They seem to say to me "Don't give up! Look what you can achieve when you persist!"