Killer fungus discovered that destroys UK invasive plant

A new species of fungus has been discovered in Britain that destroys an aggressively invasive plant. This discovery raises hopes that decimated native habitats could eventually be restored. The fungus infects the heath-star moss, which is damaging UK environments by taking over and displacing other species. Scientists say this event could represent a rare fightback by the British environment against invasive species.

Dr. George Greiff, a 30-year-old researcher, made the discovery while walking on the Isle of Wight four years ago. He spotted dead invasive mosses on a cliffside and took samples, but he could not initially identify the cause of death. However, he kept seeing more cases of decaying moss in similar locations. Working with scientists in the UK and France, he has now managed to piece together the puzzle.

The culprit was a potent fungus never seen before by scientists, now named "moss die-back." We often think of fungus as bad, but consider this one to be a "goodie." Its victim, the heath-star moss, is all over Britain. You can find it on hillsides, sand dunes, or even growing in tarmac. "It's aggressive," says Greiff. "It is a pretty-looking thing," he concedes, "but it's caused a lot of problems."

Around 2,000 non-native plants and animals have been brought to Britain from all over the world by people, either accidentally or sometimes deliberately. Some end up dominating the environment. The most famous example is probably the North American grey squirrel, which has nearly wiped out native red squirrel populations. In the plant world, some of the biggest offenders include invasive Japanese knotweed, which damages people's homes, or rhododendron, which leaves toxins in soils.

Not a lot was known about the heath-star moss before this discovery. Scientists think it arrived on British soil in the 1940s from somewhere in the southern hemisphere. By 1990, it was everywhere. "This moss has just exploded," Greiff explains. "In the 1930s, native mosses would have been growing here instead."

There are more than 1,000 types of moss in the UK. They form the backbone of our most precious habitats, such as rare temperate rainforests (damp coastal woodlands) and peatlands that store carbon. However, they are threatened by non-native plants. The heath-star moss sends out spores far and wide and reproduces quickly, making it a highly successful invader. "The first time I saw it, I had no idea what it was," says Greiff, who works at Amgueddfa Cymru museum in Cardiff. "I threw it in the bin."

In heathlands like the one where the discovery was made, native mosses have gone locally extinct or have been significantly reduced in their populations. Greiff’s talent for quiet, careful observation of plants no taller than our ankles is evident. Just a few metres into a walk, he finds the evidence. "It's as big as my hand," he says, spreading his fingers over a brown ring of dead moss. Honestly, it is less dramatic than expected. But when looking through a macro lens, white blobs are visible suspended on the moss tips. It is the fungus at work.

Greiff points out baby heather plants nearby that are now able to grow in the gaps left by the decayed moss. Now that Greiff knows what the helpful fungus can do, he looks for it anywhere he goes. He jokes that the map of where it has been found is also a map of his holiday destinations.

"It's taken a lot of DNA sequencing to fully identify this fungus," he says, showing dead moss under a microscope in a lab at Amgueddfa Cymru museum. The fungus clings onto the moss stem, ballooning like candy floss around a stick. It has even penetrated some of the moss cells. He has worked out that it is a close relative of the ash die-back fungus that has killed up to 80 million ash trees in Britain.

A powerful fungus destroying plants sounds like a potential threat to other species and biodiversity. However, Greiff's analysis suggests that it only affects the heath-star moss, and to a limited extent one other type of moss, although more work is needed to confirm these findings. He believes that the origins of this fungus may be in a native species that has since adapted to kill the heath-star moss. This could be a "rare example of the British environment fighting back," he says.

Usually, invasive species are deliberately targeted by humans to try to bring them under control. For example, there are initiatives to feed contraceptives to grey squirrels. "Some people might try to collect this moss to try and get rid of it, but it's not very effective," Greiff says. "It would be very resource-intensive and very expensive." To have a natural biological control agent doing the work for us is really valuable.

In cabinet drawers holding the oldest collection of mosses in the UK, the museum's Head of Plant and Earth Science, Dr. Nathan Smith, shows dried mosses in paper envelopes, some dating back to the 1880s. By looking for evidence of the moss die-back fungus on these historical samples, scientists want to pinpoint exactly how and when it appeared.

"This fungus gives an opportunity to save these unique moss landscapes that are homes for insects, fungi, molluscs, and other plants," explains Smith. "It gives a real chance to preserve and present their uniqueness and beauty."

Mosses are just one part of Britain's complex biodiversity. However, as our nature is classed amongst the most depleted in the world, with one in six species at risk of extinction, discovering a control on habitat destruction is a cause for hope. "It's exciting in so many respects," says Greiff. "Though I am the only one looking for the fungus. It would be nice if some other people did too."