Moss

Moss is a small, soft plant that grows in thick green patches on rocks, soil, tree bark, and damp ground. Mosses are some of the oldest land plants on Earth. They first appeared more than 450 million years ago, long before dinosaurs, flowers, or even trees. Today there are about 12,000 different kinds of moss living on every continent, including Antarctica.

Mosses are unusual plants. They have no flowers, no fruit, and no seeds. They also have no real roots. Instead of roots, mosses have tiny thread-like parts called rhizoids that grip onto a surface but do not pull up water. A moss soaks up water and minerals straight through its leaves, like a sponge. This is why mosses almost always grow in damp, shady places.

Without roots or tubes to move water around, mosses cannot grow tall. Most are less than an inch high. The tallest moss in the world, called dawsonia, lives in Australia and New Zealand and can reach about 20 inches, taller than a school ruler. Even that giant is short compared to ferns or trees.

Instead of seeds, mosses make spores. A spore is a tiny dot of life, much smaller than a seed. When a moss is ready to spread, it grows thin stalks with little capsules on top. The capsules pop open and release millions of spores into the wind. If a spore lands somewhere damp, it grows into a new moss.

Mosses do quiet but important work. A thick mat of moss holds water in the soil, keeps the ground from washing away in the rain, and gives a home to insects, spiders, and tiny creatures called tardigrades. In cold northern places, a special kind of moss called sphagnum, or peat moss, builds up in bogs over thousands of years. The packed-down peat stores huge amounts of carbon. Scientists think the world's peatlands hold more carbon than all the forests on Earth combined.

People have used moss for a long time. Sphagnum moss can soak up many times its weight in liquid, so soldiers in World War I packed it into bandages when cotton ran short. Gardeners use peat moss to help soil hold water. Some people even build soft green moss gardens, which are popular in Japan.

The next time you walk through a wet forest, look closely at a fallen log. The thin green carpet on top is older, in a way, than every tree around it.