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Sphagnum is a genus of nearly 350 species of mosses covering 2–3 per cent of the earth’s surface. It grows as dense, spongy carpets, forming colourful patchworks on mountains, moorland and bogs throughout the British Isles.
The plants form an environment that is antiseptic and acidic, meaning that they are slow to decompose, as is anything in them.
Sphagnum efficiently absorbs moisture because of its close overlapping leaves and sponge-like matting of the branches around the stem, and also the microscopic structure of the leaves. The elongated living cells form a network running throughout the leaf but it is a second set of cells, dead and empty, that provide the plant’s capacity for absorption.
Their porous cell walls allow water to flow in and inflate them. Each cell can absorb up to 25 times its own weight of liquid.
Sphagnum has found use since ancient times in home-made sanitary towels and as a form of nappy. Native North American babies often spent their first two years carried around in a moss-lined bag of rabbit or moose skin.
Sphagnum has been used to staunch wounds for over 1,000 years. Scottish soldiers used it at the battle of Flodden in 1513. Its use for wounds waned until the 1914–18 war, when it soon became obvious to surgeons that the need for dressings would be immense due to the unexpected numbers of military wounded.
The propensity for the injuries to become septic and suppurating made it imperative to find sufficient quantities of a material with increased absorbency that cost less than cotton. Sphagnum met these requirements.
Absorbent cotton absorbs liquids only until the area in contact with the wound becomes locally saturated, whereas sphagnum is able to redistribute the fluid away from the wound, increasing absorption capacity. Such was the success of the moss dressings that by the end of the war, when production ceased, over a million pads a month were being made in Britain.
More recently, research has focused on a pectin-like carbohydrate extracted from the moss, called sphagnan. Sphagnan has been detected in peat bogs and is thought to be a major factor in their preservative properties.
Its molecule contains carbonyl groups that react with amine groups of bacterial protein molecules, giving it the potential to immobilise bacterial cells, as well as enzymes, exotoxins and lysins secreted by invasive pathogens.
This has led to interest in the use of sphagnan as a food preservative and early experimental results have proved promising.