We've only named about 200,000 of an estimated 2 or 3 million species
Beneath every forest floor lies a civilization older and stranger than our own, one we are only now learning to read. Mycologist Greg Thorn and his colleagues have found, through the lens of genetic sequencing, that the fungal world is vastly larger and more intricate than morphology alone could ever reveal — with an estimated two to three million species on Earth, fewer than a tenth of them named. The gap between what exists and what we have catalogued is not merely a scientific inconvenience; it is a reminder that the living world routinely exceeds the boundaries of human perception.
- Of the estimated two to three million fungal species on Earth, only around 200,000 have been named — meaning the overwhelming majority of fungal life remains invisible to science.
- For decades, mycologists were forced to distinguish species by spore shape and size alone, a method so imprecise it often collapsed into educated guesswork and intuition.
- The arrival of PCR-based DNA sequencing shattered old assumptions: fungi that looked identical proved to be evolutionary strangers, while organisms that seemed wholly unlike each other turned out to be close kin.
- Unlike birds or mammals, fungi conceal their diversity behind subtle, easily misread physical forms — making molecular tools not just useful but essential to understanding them.
- As genetic research accelerates, existing classifications will continue to be overturned and entirely new species will emerge from ecosystems we thought we already knew.
Greg Thorn was reading about carnivorous plants when he recognized something familiar. The fungi he studied were hunters too — not with leaves or sticky hairs, but with microscopic nets woven through the soil to snare nematodes. He and biologist George Barron gave them a name: carnivorous fungi. It was a small discovery that pointed toward a much larger truth about how little we understand of the living world.
The forest, Thorn explains, is a system of nested ecosystems. Trees give way to lichen, lichen harbors tiny animals, and fungi consume those animals in turn. Fungi are threaded through every layer — decomposing, predating, forming partnerships with plants and other organisms — and yet they remain profoundly unknown. Scientists estimate between two and three million fungal species exist on Earth. We have named roughly 200,000.
For most of mycology's history, that ignorance was structural. Researchers distinguished species by examining spores under a microscope — their shape, their dimensions, their subtle variations — and the line between a new species and a mere variant often came down to intuition. Then genetic sequencing arrived.
PCR technology allowed scientists to amplify and read DNA directly, and the results were disorienting. Two fungi that appeared nearly identical could belong to entirely different branches of the evolutionary tree. Others that seemed wholly unlike each other — puffballs and grocery-store button mushrooms, for instance — turned out to be close relatives. The field moved, almost overnight, from morphology to molecular certainty.
The implications are still unfolding. Because fungi hide their diversity behind subtle physical forms, the tools that work well enough for birds or mammals were never adequate here. With DNA sequencing, researchers are discovering that the true complexity of fungal life is orders of magnitude greater than what the eye can resolve. The work of naming and understanding that complexity has, in a real sense, only just begun.
Greg Thorn was reading a coffee table book about carnivorous plants one afternoon—pitcher plants, sundews, Venus flytraps—when a thought struck him. The fungi he studied weren't so different from those plants at all. Both were hunters in nutrient-poor environments, both had evolved elaborate traps. The plants used photosynthesis to manufacture the sugars they needed, then caught insects to extract nitrogen and phosphorus. Thorn's fungi decomposed rotting wood, pulling carbon and energy from the cellulose, but they needed protein too. So they had developed their own strategy: microscopic nets that caught nematodes drifting through the soil. He and biologist George Barron coined a term for them: carnivorous fungi. It was a small moment of recognition, but it pointed to something larger—how much of the living world operates on principles we've only begun to understand.
The forest, Thorn explains, contains multitudes within multitudes. If you step back, you see trees. Step closer and you notice the grey-green and orange patches of lichen clinging to bark. Look into those lichens and you find small animals moving through them. And then there are the fungi, eating those animals. Each layer contains its own ecosystem, its own logic. Fungi are woven through all of it, decomposing, predating, partnering with plants and animals in ways we're still cataloging.
Yet for all the complexity fungi create, we know almost nothing about them. Scientists estimate there are between two and three million fungal species on Earth. We have named roughly 200,000 of them. That gap—the space between what exists and what we've identified—is the measure of our ignorance. For decades, mycologists relied on what they could see under a microscope: the shape of a spore, its length, its thickness, whether it was slightly fatter or skinnier than another. These observations were educated guesses at best. A researcher might examine two fungi with subtly different spore morphology and wonder if they were separate species or merely variations of the same organism. The answer often came down to intuition.
Genetic sequencing changed everything. The polymerase chain reaction—PCR—allowed scientists to copy and amplify DNA strands, making them readable. Suddenly, the invisible became visible. Two fungi that looked nearly identical under magnification could be placed on entirely different branches of the evolutionary tree. Conversely, organisms that appeared fundamentally distinct turned out to be close relatives. Puffballs, for instance, which seem utterly unlike the button mushrooms sold in grocery stores, are actually quite closely related when you examine their genetic code.
This revolution in knowledge has been particularly dramatic for fungi and microbes, where morphological differences are subtle and easily misinterpreted. Birds and mammals, by contrast, are relatively easy to distinguish from one another—there simply aren't millions of hidden species masquerading as something else. But fungi hide their diversity. Without DNA sequencing, we were looking at the forest floor and seeing only what our eyes could resolve. With it, we're discovering that the actual complexity is orders of magnitude greater. The field has moved from guesswork to certainty, from morphology to molecular truth. And as that work continues, the estimate of undiscovered species will only grow. We are still, in other words, barely beginning to see the fungal world as it actually is.
Notable Quotes
These nematode-trapping fungi are basically carnivorous mushrooms because they're doing the same thing that carnivorous plants do.— Greg Thorn, mycologist
With DNA sequence data, you know that this one with slightly fatter spores is in a whole different branch of the phylogenetic tree.— Greg Thorn, on how genetic sequencing clarified fungal taxonomy
The Hearth Conversation Another angle on the story
When you talk about carnivorous fungi, you're using language borrowed from botany. Does that metaphor hold up, or does it break down once you look closely?
It holds up because the underlying principle is the same—both are solving the same problem in nutrient-poor environments. But the execution is completely different. A Venus flytrap uses movement and speed. A fungus uses patience and chemistry. It builds a trap and waits. The metaphor works because it captures the strategy, not because the mechanisms are identical.
You mentioned that puffballs and button mushrooms are closely related. How did we get that so wrong for so long?
Because we were looking at the fruit—the visible part. A puffball looks like a round ball. A button mushroom looks like an umbrella. Completely different shapes, completely different structures. But the genetic code underneath tells you they're part of the same family. It's like judging two people by their clothes and missing that they're siblings.
The gap between 200,000 named species and two or three million estimated species is enormous. Does that number feel real to you, or is it more of a placeholder?
It's a serious estimate, not a guess. But honestly, it might be conservative. As we sequence more fungi, we keep finding that what we thought was one species is actually several. The real number could be higher. We're still in the early stages of actually seeing what's there.
What does it feel like, as a scientist, to realize how much you don't know?
Humbling. But also exciting. Every time we sequence a new fungus, there's a chance we're looking at something no one has ever formally identified. That possibility never gets old.