What is the moss that grows on rocks?

The moss that commonly grows on rocks is often referred to as "rock moss" or "crustose lichen." These types of mosses and lichens are adapted to thrive in harsh environments with limited soil and moisture. They play a crucial role in breaking down the rock surface, contributing to soil formation and providing habitat for other organisms. Common species include Rhizocarpon and Cladonia, which can often be found in various ecosystems worldwide.