Science Friday - Why it's so hard to tell the age of a fungus

Episode Date: September 2, 2026

When you see a mushroom popping up from the forest floor, that mushroom is just the tip of the fungal iceberg for a vast world beneath the surface. But the nature of fungal life makes it hard to answer some basic questions. What exactly does it mean to be one individual organism? And how do you tell how old a fungus is, when parts of it can recycle, regenerate, and grow again? Flora talks with fungal researcher Kristin Aleklett about the challenge of fungal age, and how researchers are trying to better understand what fungi are doing in the world under the ground. Guest: Dr. Kristin Aleklett is a researcher at Lund University in Sweden. Transcript will be available after the show airs on sciencefriday.com. Subscribe to this podcast. Follow our show on Instagram, TikTok, Facebook, and Bluesky @scifri and sign up for our newsletters. Got a science question that’s keeping you up at night? Call us: 877-472-4374 Hosted by Simplecast, an AdsWizz company. See pcm.adswizz.com for information about our collection and use of personal data for advertising.

Hey, I'm Flora and you're listening to Science Friday. When you see a mushroom popping up from the forest floor, that mushroom is just the tip of the fungal iceberg for a vast world beneath the surface. But the nature of fungus makes it hard to answer some basic life questions, like what exactly is one individual organism? And how do you tell how old a fungus is when parts of it can recycle, regenerate, and grow again? Dr. Christine Alaclet is trying to understand what fungi are doing in the world underground and tackle some of these questions. Hey, Christine. Hi, nice to be here. Thanks for being here.

Okay, so do we have a method for aging fungi? Like, we have tree rings. Is there an equivalent for fungi? No, not really, especially not one that works for all kinds of fungi. Because what we have to remember is that there's millions of species of fungi. And like, if you compare to animals, like, you wouldn't maybe look at age in a chicken in the same way as you look at an age in, like, earthworm, right? There are some ways that people have tried to estimate the age of fungi. One of the most famous examples, what they did was they looked at, like, how a fungal disease spread between trees.

And in that way, they could see that, okay, in a year, it got about one meter to another tree. It's the same we can see for, for example, these fairy rings that people see sometimes out in the forest. There has been actually people able to look at old satellite images to be able to see how much they've grown and for how long that that ring has specifically been there. But it's not always that we have those kind of above-ground indicators for all kinds of fungi. in most cases, we're not really able to track the mycelium underground throughout its life. So it's really hard to know. That's really interesting.

Those seem like kind of crude methods, too. I mean, even just tracking a fungal disease, I mean, that tells you maybe how fast a fungus grows, but does that tell you much about how old it is? Yeah, so what makes it even more tricky, you can say is that they're also constantly both growing and kind of degenerating and disappearing. And some of them can even like kind of recycle themselves as they grow. So it's really hard to have like a visual measurement of exactly like how old they are just based on their size. Given those caveats, do we have a contender for what people might think is the oldest fungus among us?

Yeah. So there's this one fungus. thought to cover 965 hectares of land in Oregon, that based on how fast they've seen this species spread between trees, they've then calculated that it could be as much as 8,650 years old. Wow. I mean, 965 hectares puts us at like 3.7 square miles. It's huge, just enormous. Yeah. Yeah. And they, don't even think that this is so uncommon. It could be similar ones in other first. It's just that we haven't really been looking or doing this type of studies everywhere. Yeah, they've been overlooked.

I mean, how did you get interested in these questions? So, I mean, I've always been really fascinated by fungi, I think, because I found that often teachers would go like, well, we don't actually really know this. And if you're a biologist and you're kind of a mind of a researcher, when someone says, we don't really know this. What you want to do is find out more. So I've always been really fascinated by what's going on with the fungi and how they live their lives. And it's this kind of secret world underground,

something that's kind of been called a black box. But in late years, we've been doing research, trying to make new methods to study soil organisms using microfluidic ship technologies. what looks like a microscope slide that we then have kind of imprinted little channels in silicon. And so it becomes like a little labyrinth, a little mace that's enclosed, where we can get the fungal mycelium to grow in there. And then we can introduce them to things or challenge them with things and see how they respond

and how long they persist. I mean, do they show signs of age? So we recently did a study where we could see that there was a big difference between species in terms of how much they did this recycling of themselves, where some of them left a lot of like kind of empty mycelium left behind that, where they had kind of withdrawn all the content of their heifi. And other ones kind of completely broke down the whole mycelium. then could reuse this material to build new heifie.

They didn't waste anything. They didn't leave as much behind. So that's really fascinating to see that it can be really different between different species that to us look like they're living the same kind of life out in the forest. But do they, if you keep giving them nutrients and what they need, do they just keep going? You know, of course, like we're getting into deep questions about

sort of immortality and those topics. But do they slow down? Yeah, so it's a good question because I think a lot of people are interested in this, whether fungi live forever or not. And I think people think more that this is possible than maybe what's the case. And I think I've seen some publications also saying that they're actually having some struggles with this also in other applied settings where they want to have these fungal cultures growing forever and producing things for us, but they do sometimes see degeneration in the cultures that they don't really know how to explain it or why it's happening. But also we don't know how old the cultures we have are, right? We know maybe in what

year it was isolated from nature, but we don't know how old it was already when we sampled it out in the field. So there's a lot of things that we haven't maybe necessarily taken into consideration when it comes to fungi. And this is really important, especially if we want to conserve fungi and make sure that they don't go extinct if we're worried about species that are at risk. Like we need to know, you know, how long does it take for them to get to an age of maturity? When do they start reproducing?

Can they reproduce at all stages of their life? We don't know these things. It's so fascinating. These questions feel like basic biology meeting. These are deep philosophical questions. You know, what is an individual? What is age? What does that really mean?

Is that the appeal for you in part? Or do you feel like you ever get lost in the sauce, the mushroom sauce? No, for sure. I think for me, because I also do research when we try to look at like behavior of fungi that is also kind of touching on the philosophical, you know, like can we think about fungi as organisms that behave? And in order to understand some of that, I also kind of need to know, you know, like what is old and what is young. But I think ultimately, like, it's just about trying to wrap your head around, like, what is it like to be a fungus? What does

their world look like? What are they interacting with? Which problems are they running into? Like, what does it take for a fungus to get 8,000 years old? What is it that they have to adjust about their bodies or their environment or what they're eating and who they're interacting with to extend their life as long as possible? And there's a lot of really unknown questions out And I think it's so super fascinating. Like I want to be part of trying to answer those questions because fungi are really like everywhere. And they're affecting more things than we think about like in forests, in agriculture. They're in the air.

They affect, you know, health and prosperity of everything. So if we want to be able to affect fungal lives and what they do and where they are, then we also need to understand, you know, how they function and understanding their life histories is a big part of that puzzle. That sounds fun. Come join us. I might. I'm tempted.

It's not too late. I'm tempted. Dr. Christine Alaclatt is a researcher at Lund University in Sweden. Thank you so much for talking to me today. Thank you. This episode was produced by Charles Berkwist and D. Peter Schmidt. And if you have questions, deep and existential, or otherwise, give us a ring.

8774 SciFry is our number. Thank you for listening. I'm Flor Lichten.