23 May 2020

7 interesting things about moss

Often overlooked, this miniature plant has more to it than meets the eye.

By Ellen McHale

Moss growing on Rock Walk, Wakehurst

On the roofs above our heads, on garden walls, and in cracks in the pavement; mosses are growing all around us. 

Often overlooked, these tiny plants have incredible properties. From hot deserts to damp caves, they can survive in extreme conditions and play an important role in biodiverse habitats across the world. 

Moss growing on rocks in the Rock Walk, Wakehurst
Moss growing on rocks in the Rock Walk, Wakehurst

1. They're ancient plants

Mosses are non-flowering plants which produce spores and have stems and leaves, but don't have true roots. 

Mosses, and their cousins liverworts and hornworts, are classified as Bryophyta (bryophytes) in the plant kingdom.

They date back 450 million years, and have survived and thrived through a range of drastic climate changes. 

Comprised of 15,000 – 25,000 species, they occur on every continent and in every ecosystem habitable by plants that use sunlight for energy. 

Among the world of plants, the bryophytes are the second most diverse group exceeded only by the angiosperms, the flowering plants (350,000 species).

2. They don’t have roots

Unlike most other plants, mosses don’t have roots. 

Instead they have rhizoids, which are small hairlike structures. Their main function is anchoring the plant to rock, bark or soil. 

So without roots, some moss suck nutrients up through the rhizoids and others draw in moisture and minerals from rain and the water around them through their highly absorbent surfaces.

Moss growing on Rock Walk, Wakehurst

3. They're tougher than they look 

Mosses grow in many different environments, from cold snowy mountains to baking hot deserts. 

Because of their range of adaptations, they are able to occupy areas that are otherwise uninhabitable such as rocky ledges on mountainsides. 

Different species have adapted to survive in extreme conditions. Studies have shown that the lowest temperature they can photosynthesise (turn energy from sunlight into food) is around -15ºC and the highest is around 40ºC. 

In hot environments like prairies or deserts, one way that mosses tolerate heat is by becoming dormant. When they're desiccated (dried out) they can survive heat much better than when they're hydrated. 

Some mosses have even been known to survive temperature highs of 100ºC when dried out, and lows of -272ºC. That's a resilient little plant right there. 

Moss, Ellen McHale © RBG Kew header

4. Soaking it up

Mosses function like sponges, using their capillary spaces to hang on to water. 

They help to soak up rainfall, maintain moisture in the soil below and keep conditions around them humid. This enables other plants around them thrive, such as in habitats like marshes and woodland. 

Mosses also play a vital role in the development of new ecosystems. They're among the first plant colonisers of disturbed sites, such as when an area is deforested or affected by forest fires. They stabilise the soil surface and retain water, helping new plants to grow. 


5. Temperature control 

Mosses can impact the temperature of the soil, both warming it up and cooling it down depending on the environment. 

In hot places, they can protect tree roots by shading and insulating the soil from high temperatures. 

In the Arctic they have an opposite effect on temperature. They can prevent the warmth of the sun from reaching the ground and reduce the speed at which ice thaws, keeping it cooler for longer. 

Moss, Ellen McHale © RBG Kew header

6. Some mosses are luminous 

Some mosses have adapted to low light conditions and are even found growing in caves. 

One of the most well-known cave mosses is Schistostega pennata, also known as dragon's gold, which shines an emerald green colour. 

This moss has adapted to cope with lack of light and it's these adaptations that create the luminescence.

Protonema are thread-like structures that grow from a moss spore. Inside the protonema, the chloroplasts gather together to receive the maximum amount of available light and the lens-shaped cells help to focus the light. 

The reflection of light from these chloroplasts is what causes the green luminous glow. 

There is even a natural monument to this amazing moss in Hokkaido, Japan, where you can see it growing in a cave. 

Schistostega pennata
Schistostega pennata by Dr TerraKhan/Wiki Commons

7. Biodiversity 

From miniature plants to gigantic trees, biodiversity is the incredible variety of all life on earth. 

Mosses are important components of the vegetation in many regions of the world, and they make up a major part of the biodiversity in moist forest, wetland, mountain and tundra ecosystems. 

Moss communities offer microhabitats that are critical to the survival of a diversity of organisms. They provide valuable shelter for insects to live, lay their eggs and hunt for food. 

Mossy animal homes 

Even creatures like turtles can benefit from the ability of the mosses to buffer temperatures. 

In Ontario, Canada, spotted turtles (Clemmys guttata) spend the winter sheltering under a type of moss called Sphagnum. This protects the turtles from getting too cold in snowy conditions that drop to lows of -35ºC. 

You can also see these kinds of mosses in the UK. Sphagnum mosses form spongy carpets on the ground of heaths and marshes, and play a vital role in the creation of peat bogs. 

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