Nature · Ferns, grasses & other plants

Sphagnum moss

Perennial moss · around 300 species worldwide

Sphagnum — Sphagnaceae (bog mosses)

Sphagnum, or bog moss, is the plant that builds peat. Its shoots grow at the tip and die at the base, and because the waterlogged, acid, airless conditions it creates stop the dead material rotting, the remains pile up as peat at perhaps a millimetre a year. A bog is therefore largely made of its own dead moss, and British and Irish peatlands hold more carbon than all the country's forests. There is no root and no vascular tissue: water is held in huge empty cells and in the spaces between leaves.

How to spot them

▸Spongy, water-squelching carpets and hummocks on bog, wet heath and moor — often startling red, ochre or lime green
▸A dense star-shaped head (capitulum) of crowded young branches at the tip of each shoot
▸Branches in bunches along the stem, some spreading, some hanging down the stem
▸No roots at all; squeeze a handful and water pours out
▸Raised spore capsules on short pale stalks (pseudopodia) in summer, bursting explosively

How to know it

This plant builds peat: it grows at the tip, dies at the base, and its acid waterlogging stops the dead parts rotting

Sphagnum, or bog moss.

Large dead hyaline cells let it hold many times its own dry weight in water, hence the spongy squelch of a bog

Sphagnum moss.

Sterile and absorbent, it was gathered in vast quantities for wound dressings in the First World War

Sphagnum moss — it holds more fluid than cotton wool and is mildly antiseptic.

It acidifies its surroundings by exchanging cations for hydrogen ions, keeping competitors and decay bacteria out

Sphagnum moss.

The peat-forming genus of the blanket bogs of the Flow Country, a UNESCO World Heritage Site

Sphagnum moss.

Spore capsules are shot into the air by compressed gas as the capsule dries and bursts

Sphagnum moss.

Quick-fire facts

•About 300 species worldwide, of which roughly 30 or more grow in Britain and Ireland
•Peatlands cover about 3% of the world's land surface but store roughly twice the carbon of all the world's forests
•Sphagnum has no roots and no true vascular tissue; water moves by capillarity through dead hyaline cells
•Used as a surgical dressing on an industrial scale in the First World War, and traditionally as nappy material and lamp wick
•Bog bodies such as Tollund Man survive because sphagnum peat is acid, cold and anaerobic, and tans skin
•The Flow Country of Caithness and Sutherland, the largest blanket bog in Europe, was inscribed as a UNESCO World Heritage Site in 2024
•Horticultural peat extraction destroys the bog far faster than sphagnum can rebuild it; retail peat sales in England are being phased out
•It is a bryophyte: it reproduces by spores, not seeds, and the leafy plant is the haploid gametophyte generation

Drill it — 7 cards

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Sources

The Wildlife Trusts — Sphagnum moss
Plantlife — The Flow Country becomes a UNESCO World Heritage Site