The discovery of a globally rare truffle in woodland in west Scotland has prompted a rewilding dilemma. The fungus lives only in close association with non-native Sitka spruce, set to be removed in a project to restore Scottish rainforest oak woods. 

When the spruce trees are removed, the fungus will die too.

“When we have something as rare as that do we have a responsibility to save it?” asked Dr Andy Taylor, the molecular fungal ecologist at the James Hutton Institute leading the research. 

The truffle, Chamonixia caespitosa, is a species critically endangered and on the red lists of multiple European countries and has only been recorded in 160 locations worldwide. Typically, it is found in the Alps and Scandinavia and has only been recorded once in the UK, in northern Wales, just seven years ago.

It is striking and notable for its colour change, from white to blue, on bruising. 

The truffle was found during a Scottish government-funded project looking at the effectiveness of measures to restore the Atlantic oak woods, many of which had previously been converted to conifer plantations.  

The fungus is rare, but the Atlantic oakwoods are themselves important and rare. Rich in biodiversity, this so-called "temperate rainforest" would have once cloaked the Western fringe of Europe from Scotland down to Portugal.  

Scotland has a big proportion of these globally remaining oakwoods, but it is estimated the habitat now covers just 30,325 ha, with 21% of sites having been planted over with conifer. 

Dr Taylor recalled his surprise at the truffle discovery, revealed as a result sampling of soil biodiversity carried out by the James Hutton Institute in six areas of Glen Creran. Samples were taken from oak woods, restored areas, and conifer plantations. Meta-barcoding of DNA was used to identify the life in the soil. 

“When I saw that name come up in the data, I thought, 'Wow,'” said Dr Taylor. “It’s extraordinary because I know the name and I know the species but I had never seen it. It’s incredibly rare. The chances of finding it were astoundingly small.” 

The Herald: Chamonixia caestiposaChamonixia caestiposa (Image: Caroline Hobart)

The team, he said were “incredibly lucky” to find it. “From 42 sample sites at Glen Creran, we have generated some 300,000 fungal DNA sequences, which can be grouped into 1,175 different fungal species,” he said. 

“Just three of those sequences, from one single sample, came from Chamonixia caespitosa But without further work, we can’t tell how widespread it actually is.” 

It is not known how the fungus, which is usually spread by animals, digging up and consuming the truffles, got into Glen Creran. Most likely, Dr Taylor suggested, it must have been carried in on a seedling. 

But Chamonixia caespitosa are not set to grace any dining table in Scotland – since unlike some other truffles, they are not edible.

“People know about truffles,” said Dr Taylor, “because some of them are incredibly popular as edibles. There are a few that are hundreds if not thousands of pounds to buy in small quantities. But the name truffle just refers to any fungus that produces a fruit body below ground. And Chamonixia is just one of hundreds of these.” 

The most expensive ever, a 1.3kg white truffle, was sold in 2009 for $330,000 in to the late Hong Kong casino tycoon, Stanley Ho. 

In fact, Dr Taylor observed, most truffles are not edible for humans – and the term ‘truffle’ merely indicates a type of fungus that creates a fruiting body underground.  

The Herald: Dr Andy Taylor of the James Hutton InstituteDr Andy Taylor of the James Hutton Institute (Image: James Hutton Institute)

“One of the things that people love the edible truffles for is that their flavours are incredibly complex, and there’s a reason for this. Truffles are spore-bearing structures, producing spores below ground that need to be dispersed. Many of them produce aromatic compounds to attract animals, which then dig them up. They eat the truffles and wander off and then poo out the spores.”  

Out of the 42 samples from Glen Creran, the number of fungal species found was 1175. Of these 21 were truffle species. "However," said Dr Taylor, "none of them were of culinary interest – for us humans at least."

 Chamonixia caespitosa has only ever been found with spruce, with which they have what Dr Taylor call  a “beneficial association”. Both the spruce and fungus profit from the relationship.

“These are,” he said, “mycorrhizal fungi - myco meaning fungi. And rhizal root. The fungi colonise the root and take up nutrients from the soil and pass some of those nutrients on to the plant in return for sugars. It’s a beneficial association for both fungi and plant. 95% of all terrestrial plants form mycorrhizal associations.” 

The only other finding of the species in the United Kingdom was by truffle specialist Caroline Hobart, in Wales in 2016. She welcomed the new finding.  

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In a paper published about her own discovery, she described it as looking like “a rather fat, pure white broad bean”.  “Almost immediately on handling,” she wrote, “indigo blue spots began developing on the fibres over the surface. These are caused by the chemical chamonixin isolated from the fungus.” 

A key issue is whether a rare species like Chamonixia caespitosa should be protected even though it is a non-native.

“This," said Dr Taylor, " is an alien fungus on an alien tree. The spruce is not native to the UK and the fungus is certainly not native to the UK. So it does raise a question, 'In future, with climate, do we have a responsibility  for saving species that might struggle to survive in their natural native habitats with climate change?'”  

The discovery also, he said, shows how little we know about what’s in our soil. “Most of the organisms are difficult to identify if not impossible. This cryptic diversity we have in the soil is super important but we know incredibly little about it, and this is a prime example."  

“Our assessment of these sites is now telling us a lot about these woodlands that we didn’t know, including making discoveries like the Chamonixia caespitosa,” he added. “Thanks to the molecular techniques that we now use, where we can analyse DNA in soils to see what’s there in incredible detail, we expect to find more.” 

The restoration work in Glen Creran is part of wider restoration efforts focused on plantations on ancient woodland sites (PAWS). These ancient sites are at least 250 years old, but from the 1950s to 1980s, they were planted over with conifer trees. 

Restoration at the site is continuing and the Sitka spruce are set to be entirely removed. “The problem,” said Dr Taylor, “with spruce and this applies especially to Sitka spruce is that it’s quite invasive. So even if you leave one seedling it will spread. This means all of them must be removed.” 

Once the spruce are gone the fungus will no longer be able to survive. 

However, a key question is whether the Chamonixia caespitosa may be found elsewhere in Scotland, and wider UK, which has many of the type of middle-aged stands of “wet spruce” it tends to favour.  

Dr Taylor believes that may be the case. “I’d hazard a guess and say it’s probably much more widespread than what we think. Spruce is not a habitat that most people would go hunting for fungi. I’m pretty sure it’s under-recorded. But it certainly raises an intriguing question. Where is it?”