Lichen. Local people in Jeju have called it "Clothes on stone" since ancient times. It is a symbiont of algae and fungi. Algae synthesis food from air. But fungi get food by decaying organic matter.
A long long time ago they encountered each other. Though different, they learned to work together in harmony and have been on that journey ever since. On the trees. On the ground, even on the rocks. Then a wide variety of lichens took different paths and spread all over the world.