A moss mat is built to catch water
Moss has no internal plumbing system like the tubes that move water through a tree. Its tiny leaflike structures are usually only a few cells thick, so water can cross their surfaces and reach the living cells directly. A clump’s dense shoots also trap rain and dew in the narrow spaces between them, keeping the whole patch damp longer than a single shoot would.
Getting wet—and drying out
Without a system that reliably supplies water from below, many mosses track the moisture around them. When a patch dries, its activity can slow dramatically; when rain or dew returns, it can hydrate and resume growth. This ability helps moss survive on exposed surfaces where moisture comes and goes, though prolonged dryness or harsh conditions can still damage it.
The structures that look like roots are called rhizoids. They mainly hold moss in place and may help it make contact with moisture, but they do not draw water through the plant the way true roots do. That distinction explains why moss can grow on rocks, walls, and tree bark: it does not need soil-bound roots to reach a reservoir underground. A passing shower can wet the moss directly, from the outside in.
