How do mosses form on roofs?
When a moss spore falls on a roof and there is moisture, it has enough energy stored to put out a rootlike structure, and a shootlike structure that is photosynthetic. The rhizoid may produce acid that helps break down the substrate (like a bare rock) and allow the sporeling to hold itself there and get minerals & water. The nutrients for photosynthesis are just light and water and carbon dioxide; that is the bulk of what a moss needs to make nutrients to build its body. On a roof, there will be some organic matter available too, because if the spore got there, then so can other bits of organic matter. The amount of “soil” does not need to be any bigger than microscopic, since a spore is microscopic. Once there are dead mosses, they do grow on that. Actually, the life cycle of a moss is pretty interesting. They are haploid (like our sperm and eggs, with only one set of chromosomes), and produce sperm and eggs by mitosis. The sperm swim through ambient moisture to the eggs, which are lo
