Identifying mosses

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Identifying mosses

Mosses often go unnoticed because many people do not realize how ancient, important and fascinating they are.

Moss gametophyte © Ita McCobb

Mosses belong to a group of plants called bryophytes

Mosses may be small, unassuming and not as well known as flowering plants but they are just as complex and extremely interesting and they perform an important role in the health and function of our environment.

They belong to a diverse group of organisms called bryophytes that also includes liverworts and hornworts. Bryophytes are among the simplest of the terrestrial plants.

Mosses are among the earliest plants to become adapted to living on dry land having evolved from algae.

Small in size they may be but mosses are one of the largest groups of land plants and can be found throughout the world in a variety of habitats.

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Moss characteristics

Instead of roots, mosses have rhizoids – fine brown filaments, resembling roots that anchor them to the ground but do not draw up water.

Mosses absorb water and nutrients mainly through their leaves, which are usually only a single cell in thickness.

Mosses do not have flowers or fruit and instead of seeds they have spores.

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Moss habitats

Moss in wetland © Ita McCobb

Mosses are hardy plants and can be found in habitats ranging from the tropics to polar and alpine regions and are distributed throughout the world except in saltwater environments.

As they depend on water for survival mosses are typically found in moist and shady locations like forests, beside streams and damp places such as bogs and fens; however, some have adapted to survive periods of dry weather and others can live in areas with little or no rainfall. An area of moss that looks dead may quickly come back to life again once moisture is reintroduced.

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Recognizing mosses

Moss © Ita McCobb

Mosses are part of the family technically known as Bryophytes. They are small flowerless plants that grow in dense clumps or mats, generally in damp or shady places. Each plant is usually made up of a simple, one-cell-thick leaf attached to a stem.

Gametophytes is the term used for the low, leaf-like form of moss and sporophytes the tall, stalk-like forms.

The stem plays a very limited role in conducting water and nutrients because, unlike most plants, mosses are non-vascular.

While most mosses grow to between 0.2 and 10 cm tall, the tallest moss in existence is the Dawsonia moss (Dawsonia superba), which can grow up to 50 cm high.

Mosses are often confused with other members of the Bryophytes family – the Hornworts (known as Anthocerotophyta) and Liverworts (known as Marchantiophyta).

Mosses are also often confused with Lichens. While lichens are similar looking to mosses and even have names that include the word “moss” such as “Reindeer moss” and “Iceland moss”, a lichen is not a plant but a composite organism that forms from algae or cyanobacteria (or both). Cyanobacteria are bacteria that obtain their energy from photosynthesis.

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Lifecycle of moss

Moss mat © Ita McCobb

Mosses have a two-stage lifecycle, known as “alternation of generations”. These two stages are known as gametophyte (this is the green part of the moss we see) and sporophyte (this is formed of a capsule, containing the spores and the filament). The sporophyte generation produces spores that are capable of germinating and develop into the gametophyte generation that produces male and female sex organs and ensure sexual reproduction.

Mosses can also reproduce asexually by fragmentation or by growing little vegetative buds called gemma, which can break off and grow into a new plant.

Although mosses and ferns reproduce in a similar manner they are unlikely to be confused with each other since mosses are what are called “non-vascular” plants – that is, they do not have water-conducting roots or vessels – and so tend to be very tiny plants whereas ferns are “vascular” plants – that is, having an efficient internal conducting system of vessels that transports water and salts upwards and food downwards – and so they tend to grow quite large!

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Types of moss

Acrocarpous moss © Ita McCobb

There are two types of moss. Acrocarpous mosses grow as upright plants, either separately or very close together to form an overall cover, tuft or cushion. In this group the spore-growth (sporophyte) comes from the top.

The other group is Pleurocarpous mosses that lie on the ground or other surfaces. Some of these develop each year to form mats. The leaves are usually rib-less and the sporophyte (the spore-producing part) grows from the side of one of the branches of the plant. Many of these mosses are called “feather mosses” and “fern mosses”.

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Mosses and ecosystems

Mosses play an important role in our ecosystems, as they are crucial for soil stabilisation and water retention, helping in the prevention of floods and landslides.

With other bryophytes mosses are important in the carbon cycle with peat mosses storing a huge amount of carbon in both Arctic and temperate zones.

Mosses are also important habitats for a wide variety of plants, insects and fungi and are used by other wildlife such as squirrels for lining their dreys, birds for lining their nests and dormice that hibernate in nests beneath moss.

Mosses are reliable indicators of air pollution risks to ecosystems as they acquire most of their nutrients directly from the atmosphere.

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Threats to moss

Moss in lichen © Ita McCobb

The threats to mosses are many and include habitat loss and habitat degradation.

Some aspects of modern agriculture such as overgrazing, under-grazing, the widespread use of herbicides and fertilizers all pose a threat to moss survival as well as the felling and clearing of trees in forests.

As mosses do not have roots they get most of their nutrients directly from the air and rain rather than the soil so they are particularly sensitive to atmospheric pollutants and many have become extinct from some urban and industrial environments.

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Conserving and protecting moss

Mosses along with other bryophytes have not been top of the conservation industry list but many of the conservation measures aimed at other plants and animals, such as increasing broadleaf woodland, also benefit mosses.

Conservationists have however been concerned with the loss of valuable wetlands due to peat moss harvesting and these concerns have led to the creation of codes of practice for harvesting peat in order that it will remain a sustainable resource.

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Misuse of moss in plant names

It is interesting to note that there are several plant names in which the word “moss” is misused!

Although certain seaweeds are called sea mosses, no mosses are found in salt water. Spanish moss (Tillandsia usneoides) is not a moss but a flowering plant in the same family as the pineapple. Reindeer moss (Cladonia rangiferina) is not a moss but lichen found in the arctic tundra, Irish moss (Chondrus crispus) is a red algae and Club moss (Lycopodium) is a relative of ferns!

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References: Scottish Natural Heritage; The New York Botanical Garden; ECCB – European Committee for Conservation of Bryophytes; Janice M. Glime, Bryophyte Ecology; Brian Capon, Botany for GardenersBotany for gardeners, Brian Capon, Third edition, Timber Press; Colour Identification Guide to the Grasses, Sedges, Rushes and Ferns
of the British Isles and north-western Europe, Francis Rose, Viking, The Penguin Group; Latin for gardeners, Lorraine Harrison, Royal Horticultural Society; Oxford English Dictionary, Oxford University Press.