The walls of Churches or indeed any other building of such an age are often covered with lichen, to the point that there is acrually a British Lichen Society!
https://britishlichensociety.org.uk/conservation/churchyard/churchyard-lichens
In total there are around 2000 different species and many churchyards will have around 100 of those alone. So it’s clear to see that they are great habitats for them.
Hope you like these occasional, short and sweet posts, published on days when I've a lot going on but want to feed the chain with useful nuggets of information like this!