Mosses are small, herbaceous plants that generally prefer to grow in shaded areas. There are about 12,000 different kinds of moss, but all lack veined leaves. Moss usually grows as a collective mat or sheet, but some types grow in tufts or pillows or upon the surfaces of rocks or tree bark.
Mosses absorb water and nutrients primarily through their leaves rather than through a root system. Unlike other plants, they have no vein system to transport water. Their tiny leaves are ribbed but not veined.
Mosses spread by spores and do not flower or produce seeds. Some species have male and female plants. Others are monoicous and have both male and female structures on the same plant. Lacking flowers and complex leaves, mosses may sound rather simple and unattractive, but many types of moss are quite beautiful. Some form colorful red, orange or yellow spore capsules that grow upright from the tip of a thin, hair-like stem.
Mosses are divided into three types. Peat moss, which is often referred to simply by the genus name sphagnum, is a well-known and economically important type of moss. In peat moss, live photosynthesizing cells grow within large patches of dead cells that retain moisture. This unique characteristic results in the formation of acidic bogs and peat swamps. Although they are important economically and environmentally, few people would purposefully cultivate peat mosses.
Acrocarpous mosses have branchless stems with spore capsules at their tips. They grow upright, almost like small trees, and have very small leaves. These mosses often grow in clumps or cushions, and hair cap and rock cap mosses both belong to this group. They prefer medium shade to dappled sunlight.
Pleurocarpous mosses have highly branched stems with spore capsules forming on side branches. They grow in dense mat structures and often have the delicate appearance of tiny ferns because of their branched stems. Pleurocarpous sheet mosses are especially easy to establish. They thrive in full shade, but some species are also tolerant of dappled sunlight. They never grow in full sun.
Both acrocarpous and pleurocarpous mosses are cultivated for aesthetic uses. The capsules of acrocarpous mosses are often brightly colored and give the appearance of tiny flowers. Moss occurs in many different shades of green, and garden designers often plant multiple species of moss together. This allows the appearance of the moss-covered area to change slightly with the season. Deep emerald greens, blue-greens, light mint greens, and forest greens add interest to the landscape as different species of moss come to dominance with changing temperatures and precipitation patterns.
Moss adds the appearance of age to structures where it grows. When growing on a new retaining wall, the moss causes the wall to appear as though it has been in place for a long time. It gives the impression of seclusion and quiet, and will even grow up the shaded trunks of trees. When growing on the ground, moss is soft and pleasant to walk upon, and it requires very little care once established.