|Clumps of moss on the ground and base of trees in the Allegheny National Forest, Pennsylvania, USA.|
Mosses are Bryophytes, which are non-vascular plants. They evolved from liverworts: evidence from mitochondrial DNA suggests that this is the stem group from which mosses, hornworts and all other land plants evolved.p75
Mosses do not have cells that move water like other plants- water must soak into them, like a sponge. A patch of moss is made of many tiny moss plants packed together so that they can hold water for as long as possible. They do not have roots, and could not get water from them if they did. Because they cannot find water, they live in two ways. They can live in places that are always wet; like near a spring, a river, or in a place where there is a lot of fog. They can also dry up when there is no moisture. This means they can never live in dry places like deserts.
They cannot grow very large because they could not move water to the top of the moss. The largest moss grows in New Zealand, and is about 30 cm tall.
A moss does not make seeds. A moss does not have fruit. The green fuzzy part of a moss that is always there has only half of the moss DNA. When the moss has made lots of food and there is enough water, cells from different moss plants swim inside a clump of moss. Two cells combine to make a cell with a full set of moss DNA. This cell grows into a different kind of moss plant- but it gets all of its food from a green fuzzy moss plant. When the cell grows, it makes tiny spores instead of seeds. The spores are like dust. They come from a little box that grows up out of the moss. The box has a lid that falls off. Then the spores come out and float away. They will make more moss.
Scientists divide the mosses into eight groups. Five of these groups are small, with just a few species; most mosses are in the group called Bryopsida.