A fungus that kills the invasive moss from the inside out
Since the 1940s, a small moss accidentally imported to Britain has been quietly overwhelming the heathlands and sand dunes it colonised, outcompeting native life with a patience that only nature can sustain. Now, a scientist walking a clifftop on the Isle of Wight has found that nature may also hold the answer: a fungus that attacks the invader from within, forming eerie rings of death across the green mats. The discovery invites a rare kind of hope — that the landscape, given time, sometimes generates its own corrections.
- Heath star moss has spent eight decades smothering British heathlands and sand dunes, forming mats so dense that native vegetation cannot break through.
- A chance clifftop observation on the Isle of Wight revealed patches of dead moss — the signature of a fungus that kills the invader from the inside out, spreading in unmistakable 'fairy rings of death'.
- The fungus attacks on two fronts simultaneously, growing inside moss cells while producing structures on their surface, making it a remarkably efficient biological weapon.
- The critical tension now is safety: the fungus appears to affect one related native moss species, raising urgent questions about whether it could spread further before any biocontrol programme begins.
- Researchers are racing to sequence genomes, test susceptibility across native species, and reconstruct the fungus's history using preserved specimens — trying to determine whether this is a native ally or a risk in disguise.
In the 1940s, a moss most likely hitched a ride into Britain on military equipment and spent the following eight decades doing what invasive species do best — spreading quietly and relentlessly. Heath star moss colonises bare soil, rotting wood, tarmac, and thatched roofs, but it is on heathland and sand dunes that it causes the most damage, forming thick dark mats through which nothing else can grow.
George Greiff, now at the John Innes Centre in Norfolk, was walking a cliffside on the Isle of Wight four years ago when he noticed something unexpected: patches of dead moss breaking the usual carpet of green. The culprit, identified after years of painstaking work including DNA sequencing, was a fungus from the genus Bryoscyphus — a group that specialises in attacking moss. Where it takes hold, it leaves expanding brown holes ringed with white fuzz, patterns researchers have taken to calling fairy rings of death. The fungus works by growing inside moss cells while simultaneously attacking their surfaces, assaulting the plant on two fronts at once. Collaborators in France and the Netherlands confirmed the same species was operating across multiple countries.
The most pressing question is whether this natural assassin could become a problem of its own. Current evidence is cautiously reassuring: the fungus does not appear to affect humans, animals, or other plants, and while it does infect one related native moss species, the symptoms are milder. This hints that the fungus may be native to Britain, having evolved alongside a related species before the invader arrived and then opportunistically switching hosts.
Greiff is now working in the laboratory to test how many native mosses are vulnerable, map the infection mechanism in molecular detail, and use museum specimens to determine whether the fungus predates the 1940s arrival of its current target. The goal is a biological control that restores damaged ecosystems without chemicals or introduced predators — using, if the science holds, only what the British landscape quietly kept in reserve.
In the 1940s, a moss arrived in Britain—probably clinging to military equipment—that would spend the next eight decades quietly choking out everything else. Heath star moss, as it came to be known, is a generalist colonizer. It grows on bare soil and rotting wood, on tarmac and thatched roofs, anywhere it can find purchase. But it is most destructive on heathland and sand dunes, where it forms thick, dark green mats so dense that nothing else can break through. By the time George Greiff began his work, the moss had become a fixture of the British landscape—and a problem.
Greiff, now at the John Innes Centre in Norfolk, was walking a cliffside on the Isle of Wight four years ago when he noticed something unusual: patches of dead moss interrupting the usual carpet of green. He collected samples. What he found, after years of careful work, was a fungus that kills the invasive moss from the inside out. The discovery offers something rare in conservation: a natural solution to an ecological problem, one that may have been waiting in the landscape all along.
The fungus belongs to a genus called Bryoscyphus, a group of organisms that specialize in attacking moss. Greiff had actually been collecting it since around 2017, but identifying it proved difficult—the fungus lacks obvious distinguishing features. DNA sequencing finally revealed what he was looking at. When the fungus takes hold, it creates what researchers have begun calling fairy rings of death: brown holes that spread outward through the moss mat like expanding circles, leaving white fuzz at the infection frontier. To the naked eye, in a well-established fungal population, the pattern is unmistakable.
The mechanism of attack is elegant and relentless. The fungus grows inside the moss cells, killing them from within, while simultaneously producing structures on the cell surface. It is, in effect, assaulting the moss on two fronts at once—chemically and physically. Greiff and his collaborators connected with researchers in France and the Netherlands who had found the same fungus, sequenced everything, and confirmed they were dealing with a single species operating across multiple countries.
The obvious question is whether this biological control agent might become a problem itself. Could it jump to native moss species? Could the invasive moss evolve resistance? Greiff's answer to the first concern is cautiously reassuring. The fungus does not infect humans, animals, or other plants as far as current research shows. It does affect one native moss species related to the heath star moss, but the symptoms are less severe. This suggests the fungus may be native to Britain, having evolved to live on the related moss before the invasive species arrived—and then, opportunistically, shifted to a new host. Or the reverse could be true, which would be less encouraging.
Resistance is a legitimate concern, but Greiff frames it as an evolutionary arms race rather than a catastrophe. Both the moss and the fungus are constantly adapting. If the moss develops resistance, the fungus will likely evolve to overcome it, and the cycle will continue. The more pressing worry is whether the fungus might spread to other native moss species that are vulnerable but not yet exposed.
Greiff's current work is designed to answer these questions. He recently transitioned from museum work—using preserved specimens as a kind of time machine to determine whether the fungus was present before the 1940s—to laboratory research. He is now testing how many related moss species are susceptible to the fungus, working out the details of how it infects, and sequencing genomes to understand the biology at the molecular level. The science is cutting edge, the stakes are real, and the potential payoff is significant: a way to restore heathland and sand dunes without chemicals, without introducing a new predator from elsewhere, using only what the British landscape has apparently provided on its own.
Notable Quotes
The fungus seems to be growing inside the moss cells, so it kills it from the inside. It also grows on the surface of the cells, so it seems to produce structures on the outside as well.— George Greiff, John Innes Centre
What would probably happen is one of these kind of co-evolutionary arms races where if the moss changes, the fungus will change, and vice versa, and they'll keep following each other.— George Greiff, on the risk of moss resistance
The Hearth Conversation Another angle on the story
When you first saw those dead patches on the cliff, did you immediately suspect a fungus?
Not at all. I'd been collecting the fungus for years without really understanding what I was looking at. It was only when I started seeing it everywhere, in every heathland I visited, that I decided to study it properly. The identification took time—DNA sequencing was what finally cracked it.
Why is this fungus so much better than, say, spraying herbicide?
Because it's already here. It's not something we're introducing from outside. It evolved in this ecosystem, probably on a native moss, and then found the invasive species. That means it's adapted to British conditions, and it doesn't require constant reapplication.
But doesn't the invasive moss just evolve around it?
Possibly, yes. But the fungus evolves too. They're locked in a kind of dance—if the moss changes, the fungus changes to match. That's actually more stable than a one-way arms race.
What worries you most about this?
Whether it might infect native mosses we care about. We've found it affects one related species, but less severely. I need to understand why, and whether there are other species at risk.
How long before this could actually be used to restore heathland?
That depends on the research. We need to be certain it's safe first. But the biology is promising, and the need is urgent. Heathland has been disappearing for decades.
If this works, could the same approach work for other invasive species?
That's the hope. There are invasive plants and mosses all over the world. If we can understand how to use natural pathogens safely, we might have a whole toolkit for restoration.