Some types of moss (lichens) are over 400 million years old and are known for their resillience. In situations where most species of plants struggle to survive, such as hard surfaces, low temperatures, no sunlight and acidic substrates: moss thrives! This also explains why mosses are found often on surfaces such as bricks, tiles, rocks and wood.
Not-so-fun fact: Climate change is increasing the problems with green deposits. Higher concentrations of nitrogen and carbondioxide in the atmosphere increases the growth of algea. Warm winters also allows algea to keep growing instead of freeze to death. Along with green deposits, an increasing amount of red and yellow algea are found. These types of algea were originally only found in tropical climates!