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Mosses and lichens are often confused, in part because many common names for lichens include the word “moss.” In fact, the two organisms are radically different and are not even in the same kingdom. Both are fascinating organisms, often overlooked because they are small and not very showy. They grow all over the world and are used for dyes, animal fodder, ornamentation, medicines, and religious practices.
Lichens are perhaps the most amazing living things on Earth, because they represent a symbiotic relationship between a fungus and either algae or cyanobacteria. The symbiotic nature of lichen was not fully understood until the 19th century, when the idea was first proposed. They form a fascinating example of cooperative relationships in nature, with the fungus using the algae or bacteria to produce energy, while the algae or bacteria enjoys the protection the fungus provides.
These organisms reproduce in several ways. Many produce spores that attempt to capture partner algae or bacteria, while others reproduce through fragments of the lichen that break off and scatter. They can grow almost anywhere in the world, from extremely acidic soil to freezing arctic conditions, and are found growing on trees, rocks, and everything in between. Contrary to popular belief, the lichens that colonize trees, such as members of the Usnia family, are not harmful to their hosts, and in fact, they often capture valuable nutrients.
Lichens take three forms. Crustose lichens, often found growing on rocks, are characterized by a crusty appearance. They are often vividly colored and create the bright streaks seen on rocks from a distance. Foliose lichens are leafy or stringy and are often found growing on the ground or around trees. Fruticose lichens form stalks, which sometimes form bright fruiting bodies.
Most observers don't even notice the small and ubiquitous lichen, but a determined searcher can find hundreds of species on a short walk in any region, from the depths of the woods to the streets of a major urban area. They can be extremely difficult to properly identify, often requiring the use of a microscope and specialized staining to discover the mingled identities coming together to make the lichen.
Moss, on the other hand, is a plant. It belongs to the bryophyta division, which is one of the most genetically diverse on Earth, including 10,000 species in 700 genera. These organisms can be found all over the world as well, and they form a major part of many ecologies by holding back erosion, retaining water, and feeding many animal and insect species. Moss is an archaic non-vascular plant, meaning that it has been around in various forms for millions of years, and it reproduces by casting out spores. Like lichen, it can also reproduce from broken off parts of the parent plant.
Physically, these two organisms can be difficult to distinguish. In general, mosses are green, grow in moist dark areas, and have small leaf-like structures, in addition to stems. Lichens often appear grey or pale white in appearance, and many also create disc-shaped fruiting bodies.