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

September 2, 2026

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5 min read

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

The largest known living organism on Earth by area is a fungus in Oregon's Malheur National Forest that covers 965 hectares—about 3.7 square miles. Based on how fast researchers have seen this species spread between trees, they've estimated it could be 8,650 years old. But that number comes with enormous uncertainty, because fungi don't have anything like tree rings, and the very nature of their growth makes basic questions about age and individuality surprisingly difficult to answer.

The problem with aging a fungus

Dr. Christine Olaclet, a researcher at Lund University in Sweden, studies fungi and the challenges of understanding their life histories. The core difficulty is that there is no universal method for aging fungi, and there are millions of species. "If you compare to animals, you wouldn't maybe look at age in a chicken in the same way as you look at an age in an earthworm," she says.

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What you'll learn

1 (00:00) **Introduction & The Problem of Fungal Aging** - Host Flora introduces the difficulty of answering basic life questions about fungi, such as what constitutes an individual organism and how to determine its age.
2 (02:06) **No Universal Method for Aging Fungi** - Dr. Olaclet explains that unlike tree rings, there is no equivalent method for aging fungi, especially one that works across millions of species.
3 (03:26) **Why Size Doesn't Reveal Age** - The host asks if growth rate truly tells us about age, and Dr. Olaclet explains that fungi are constantly growing, degenerating, and recycling themselves.
4 (04:04) **The Contender for Oldest Fungus** - Dr. Olaclet discusses a famous fungus in Oregon thought to cover 965 hectares and estimated to be up to 8,650 years old.
5 (04:58) **The Researcher's Origin Story** - Dr. Olaclet explains her fascination with fungi stems from teachers often saying "we don't really know this," which sparked her desire to find out more.
6 (05:35) **A Microfluidic Lab to Watch Fungi Age** - Dr. Olaclet describes her lab's method of growing fungi in a small, enclosed labyrinth made of silicone and a microscope slide.
7 (06:13) **Signs of Age: Recycling vs. Waste** - Dr. Olaclet's recent study showed a big difference between species in how they recycle their own mycelium.

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Show Notes

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.

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