What is the Difference Between Lichen and Moss?

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.

Lichen is a symbiotic partnership between a fungus and an alga or cyanobacterium, while moss is a simple, non-vascular plant. Lichens are known for their ability to colonize harsh environments and can be found on rocks, trees, and soil. Mosses, on the other hand, typically require more moisture and are commonly found in damp, shaded areas. They have tiny leaves and stem-like structures, which lichens do not.

Lichens play a crucial role in ecosystems by breaking down rocks into soil and providing food for animals like reindeer. They are also important bioindicators of air quality. Mosses contribute by retaining moisture, preventing soil erosion, and serving as a habitat for microfauna. Both are pioneer species, often the first to inhabit barren environments, initiating ecological succession.

Yes, both lichens and mosses are excellent bioindicators. Lichens are particularly sensitive to air pollution; their presence or absence can indicate air quality. Certain lichen species will not grow in areas with high levels of sulfur dioxide, for instance. Mosses can indicate soil and air moisture levels, as they thrive in damp conditions and can absorb pollutants like heavy metals from the environment.

Mosses reproduce both sexually, through spores produced in capsules that extend on stalks called setae, and asexually, by fragmentation. Lichens primarily reproduce asexually through fragmentation or by producing soredia, small clusters of algal cells surrounded by fungal filaments. Some lichen species also have the ability to reproduce sexually through fungal spores, but this is less common.

Lichens grow extremely slowly, often less than a millimeter per year, and can live for very long periods, with some species surviving for thousands of years. Mosses grow faster than lichens but still at a slow rate compared to higher plants. Their lifespan varies widely, with some mosses living for only a few years, while others may persist for decades.

Lichens are generally more resilient to environmental stress than mosses. They can survive in extreme conditions, such as arid deserts and the Arctic tundra, where mosses would struggle due to their need for moisture. Lichens can endure long periods of drought by going dormant and then quickly reactivating with the slightest moisture, a trait that mosses do not possess to the same extent.