Looking at a lichen

Have you ever looked closely at a lichen? I mean, really closely? They are quite amazing. Look at the intricate structure of this one. A symbiotic partnership between a fungus and an alga creates a lichen. This one growing on a plane tree in my office car park was photographed during a short rare sunny spell today. Using online identification keys, I think this is the species Xanthoria polycarpa, the cushion Xanthoria. It likes nitrogen-enriched environments and I suspect the nitrogen oxides from car exhausts in the car park probably provide these conditions. I think more lichen close-ups might feature in coming weeks.