Holz und Flechten

It looks like those bright yellow patches are actually lichens—most likely Xanthoria parietina, also known as yellow wall lichen. These hardy little organisms are city survivors, thriving even where air pollution makes life tough for other lichens. Their vivid color comes from a natural sunscreen called parietin, which protects them from UV rays. Amazingly, they’ve been used in folk medicine and as natural dyes, and they’re even studied for their ability to survive harsh, space-like conditions!