How diverse is the fungal kingdom?

To unlock the secrets of fungi, we need to uncover how many of them are out there, and how their sometimes strange and powerful biologies and chemistries actually work. With that in mind, we sent Will Tingle to the world famous Kew Gardens in London…

Will - As Sumi Robson just pointed out, there are potentially as many as four million species of fungi in the world, of which we've only described about 10%. That means there's a lot of catching up to do when it comes to categorising and understanding this particular kingdom of the tree of life. That's why I've come down to the world-famous Kew Gardens and its fungarium to find out what that work entails.

Lee - My name is Lee Davis. I'm the Collections Manager for the Fungarium, which means I'm a kind of glorified librarian of mushrooms.

Will - It's delightful to be at Kew Gardens’ fungarium—such an illustrious building. And I guess for the audience at home, I'd describe it as the end of that one Indiana Jones film—the warehouse, but full of mushrooms. Is the Ark of the Covenant here anywhere?

Lee - It is, but I can't tell you where it is, because we keep that for ourselves.

Will - That's fair enough. We should probably stick to fungi then in that case. I'm reading that there are 1.2 million samples of fungi in this building—is that true?

Lee - We have 1.1 million specimens. As for species, we're not totally sure—it's probably something like 60,000 to 70,000, maybe up to 100,000.

Will - Where are they found? Is there a particular biome or environment that they're happiest in, or is it literally everywhere?

Lee - Fungi originated in the oceans, along with everything else, so there’s a whole gamut of species in the oceans that we know about, and probably hundreds of times as many again that we haven’t discovered. The vast majority of the fungi that we know and have described scientifically all come from terrestrial environments. But you can find new species in the weirdest of places. I think it was two or three years ago someone described a new species of fungus found on an oil painting, underneath someone’s fingernail, and on a plastic child's backpack, I think it was. So they are everywhere and anywhere at any given time. Some of my favourites are the entomopathogenic fungi—the ones that parasitise and do horrible, horrible things to arthropods. The classic example is Cordyceps fungi—the ones that infect them, manipulate their behaviour, and eat all the insides out of their hosts before bursting out of their heads. I really like those. But right next to us—we’re next to the Amanitas, and I think Amanita muscaria is one of my favourites. That’s the red one with the white dots that everyone knows. It’s fun for all sorts of reasons. Ecologically, it’s a mycorrhizal fungus, so it has this really unusual and interesting relationship with trees. It has a lot of places in human culture—from fairy tales (it’s the one we all know from video games), but it’s also a super hallucinogenic fungus. Humans have been eating it for thousands of years for that reason. Some of the other Amanitas are also horribly toxic—will kill you very slowly and painfully. But the toxins are really interesting from a pharmaceutical point of view, because if we can apply them to cancer cells, they kill cancer cells preferentially. So the Amanitas are really interesting for lots of human-interest stories.

Will - I was fortunate enough a few years ago to be up in Svalbard, and I caught a glimpse of the Global Seed Vault—which is quite secretive but a very interesting storage facility for so many plant specimens, in case something goes really wrong on the rest of the planet. Can that idea be applied here, or is this more research-oriented?

Lee - So the collection we have here in the fungarium—this is dead and dried mushrooms. The idea isn't about preserving them to grow again; it's about having a kind of snapshot, a microcosm of the world's fungal diversity so we can study it for taxonomy and ecology. Then we can start to explore it in terms of genomes, for novel enzymes and drugs we might want to use. Kew does have a kind of fungal seed bank. So down at Wakehurst, on the Kew site, we have the Millennium Seed Bank, which is a non-agricultural version of the Svalbard Seed Bank. I think the idea is to try and have seeds from every plant on Earth as a backup. And it turns out that probably all of those seeds have fungus in them—non-pathogenically. It’s just living inside them, not causing any disease, just doing its own business. So we kind of do have our own Svalbard—but it’s in Wakehurst. Pretty equivalent, I would say. In terms of scenery, a bit warmer—and no polar bears. For now.

Will - What kind of work, then, is going on with these?

Lee - The vast majority of what we do here with this collection is taxonomy. So, what fungi are out there in the world, how are they related to one another, and just understanding fungal diversity across the world.

Will - Have there been any interesting discoveries that have changed our perception of fungi, originating here?

Lee - Yes. A good example of this—up until about 20 years ago, all fungal taxonomy was based on morphology: what does it look like, what do its spores look like under a microscope, what do the sex cells look like. It’s physically derived information. Turns out it’s horribly inadequate.
A great example that comes from here—one of our former heads of mycology bought some porcini mushrooms in the supermarket (dried Boletus edulis), brought 13 pieces here into the lab, and sequenced all 13. Turns out none of them were actually Boletus edulis. There were three different species in there, all of them new to science. So the diversity is much higher, and it’s very, very easy to split an individual species into maybe half a dozen or more based on DNA. And we can do that here with the collection. It’s relatively easy to find a new species to science hidden in these boxes—really easily.

Will - Once you start to do DNA analysis, do you have any particular favourites in this collection that you'd be willing to show me?

Lee - Okay, so—this is Bev. Bev was a tarantula. So this is just the normal tarantula. This is a Megale bird-eating spider that’s been parasitised by Cordyceps caloceroides. That’s one of these Cordyceps-type fungi. It’s invaded her body, probably manipulated her behaviour, and then finally killed her and eaten all of her guts before these two big long orange fruiting bodies popped out of her leg joints.

Will - It almost looks like a nice exoskeleton of a tarantula has gone for a swing on a couple of vines.

Lee - Yeah, it does look like she’s wearing streamers. They're really pretty.

Will - So am I right in thinking then that these long tendrils erupt, and the spores come out of them and spread further to the next unlucky arachnid?

Lee - That’s exactly it. On these fruiting bodies—mushroomy-type things—they’re just long strands rather than a mushroom, but they’re about six to eight inches long. The top two or three inches will be fertile, so they'll be producing spores. And because they’re lifted above the leaf litter by their height, the spores will drift on the wind. They’ll either land on another spider or land in the leaf litter and wait for a spider to tread on them and get picked up.

Will - These are also very much in vogue at the moment, thanks to a very popular TV show. I'm sure you're sick to death of discussing it. But for the listeners at home—the realistic chance of that happening to us is probably quite low?

Lee - It’s low—but not zero. The things in our defence are: we’re too hot—mammalian body temperature is too warm for these fungi; they don’t like it. But natural selection and climate change are going to push their tolerance. We also have quite a good immune system. Also, these Cordyceps-type fungi that manipulate behaviour and turn insects into zombies—they've been doing this for, like, 60-odd million years. We know that there are ants in amber with Cordyceps on them. So they’re not really out to get us—they already have their favourite food. That’s what they’re triggered by when it comes to germination and development. They’re not interested in humans—yet. But climate change, natural selection—who knows what'll happen as we get exposed to these over the coming decades. Never say never.