How Mushrooms Evolved Psilocybin Twice, by Two Different Routes

Psilocybin is the compound that made a whole genus of mushrooms famous. Yet it turns out that at least one unrelated group of fungi builds the exact same molecule using a completely different set of tools, assembled in a different order. A 2025 study in Angewandte Chemie pins down how, and quietly reopens one of the oldest questions in natural product chemistry: why a mushroom would bother to make psilocybin at all.

One molecule, two mushroom families

Psilocybin was first isolated in the late 1950s by Albert Hofmann and his coworkers, from the fruiting bodies of Psilocybe mexicana. In the body it is converted to psilocin, the unstable compound that actually alters consciousness by binding to serotonin receptors, chiefly the 5-HT2A receptor. Ever since, psilocybin has been bound up with the genus that gives it its name: Psilocybe. The chemistry of how these mushrooms build it, starting from the amino acid L-tryptophan, has been worked out enzyme by enzyme over the past decade.

But Psilocybe is not the only producer. The compound and its genes have turned up in several other genera, including Gymnopilus, Panaeolus and Pluteus. More surprising still is the genus Inocybe, the fiber caps, a group far better known for species that produce the potentially lethal toxin muscarine. One fiber cap in particular, Inocybe corydalina, makes psilocybin too. The oddity that set this study in motion was reported back in 2018: I. corydalina’s genome does not contain the psi genes that Psilocybe uses. Instead it carries an unrelated cluster of genes that appeared to do the same job by other means.

What it means to evolve psilocybin twice

A German-Austrian team led by Dirk Hoffmeister at Friedrich Schiller University Jena and the Leibniz-HKI, working with Bernhard Rupp in Innsbruck, set out to test that hypothesis directly. They took the five genes from the fiber cap’s unrelated cluster, produced the enzymes in the laboratory, and watched what each one actually did. Four were tested in the test tube; the fifth, a membrane-bound enzyme that resists purification, was modelled computationally.

The verdict was clean and a little startling. None of the chemical reactions that build psilocybin in Psilocybe take place in the fiber cap. The enzymes are not close relatives of their Psilocybe counterparts; the gateway enzyme, for instance, belongs to an entirely different protein family. In other words, two separate lineages of mushrooms each independently stumbled onto a way to make the very same molecule. Biologists call this convergent evolution, the same solution arrived at twice by different roads, and it is the same phenomenon that produced, say, the wing in birds and in bats.

The same steps, run in reverse

Both mushrooms make the same four edits to the same starting molecule: they add an oxygen, add two methyl groups, add a phosphate, and trim off the molecule’s tail. The surprise is the order. The figure below shows both routes flowing from the same tryptophan to the same psilocybin, with each step color-coded by which edit it is.

The most elegant finding is not just that the two routes differ, but that they are, in part, mirror images. Building psilocybin requires a handful of chemical edits to tryptophan: removing a carboxyl group, adding an oxygen atom at a specific position, attaching methyl groups, and finally adding a phosphate. What the study shows is that the two mushroom families perform several of these edits in the opposite order.

In Psilocybe, the first move is to strip off the carboxyl group; the oxygen is added afterwards. In the fiber cap, it is the reverse. The evidence is decisive: the fiber cap’s first enzyme flatly refuses to act on plain tryptophan and will only work once the oxygen has already been added. Hydroxylation therefore has to come first. The late steps are flipped as well, with methylation and phosphate addition happening in the opposite sequence to Psilocybe.

And yet, for all that divergence, the two routes are not entirely separate. They share no single reaction and no closely related enzymes, but both happen to pass through one and the same waypoint, a compound called 4-hydroxytryptamine. Two completely different assembly lines, it turns out, thread the part through the same jig exactly once.

A fork in the road: the baeocystin dead end

There is one more twist, and it concerns a molecule called baeocystin. In Psilocybe, baeocystin is a stepping stone: a near-finished intermediate that gets one last methyl group added to become psilocybin. In the fiber cap, the same molecule is a dead end. Because the fiber cap runs its steps in a different order, and because its methyl-adding enzymes will not touch an already-phosphorylated molecule, baeocystin comes off the line as a finished product in its own right rather than a precursor.

This is why the fiber cap’s pathway is best pictured as a fork rather than a straight line, producing both psilocybin and baeocystin as end products. It also explains a longstanding observation: earlier chemical surveys repeatedly found baeocystin in I. corydalina in amounts equal to, or even greater than, psilocybin itself. The balance between the two products appears to hinge on a kinetic tug-of-war between competing enzymes, which the fungus could, in principle, tilt one way or the other.

Why build psilocybin in the first place?

Here the authors are refreshingly honest: nobody knows. If two unrelated lineages each evolved the ability to make psilocybin, there is presumably some advantage to it, but the study cannot say what that advantage is. The leading ideas center on defense: that the neuroactive compound may alter the behaviour of animals that eat mushrooms, or that damage-triggered forms of it may deter predators. These remain hypotheses. Even the evolutionary origin of the fiber cap’s gene cluster is, for now, unknown.

The puzzle deepens with a detail the study notes almost in passing. Psilocybin has also been found in Massospora, a group of fungi that parasitize cicadas and are only distantly related to mushrooms. Their psilocybin genes have not yet been identified, but if they prove independent, they would mark a third, separate invention of the molecule, and the first outside the mushrooms altogether. The fact that psilocybin producers follow such different lifestyles, from wood-rotting Psilocybe to tree-associated fiber caps to insect parasites, may eventually help ecologists work out what selective pressure keeps summoning the same molecule into being.

From evolutionary puzzle to sustainable medicine

There is a practical thread running underneath the evolutionary story. Psilocybin is under serious investigation as a treatment for depression that resists conventional therapy, with encouraging results in advanced clinical trials. If it clears regulatory approval in more countries, demand will climb, and the question of how to make it at scale, cleanly and affordably, becomes pressing.

This is where a discovery like this earns its keep. Every biosynthetic pathway that is mapped enzyme by enzyme adds new, well-characterized parts to a growing toolkit, parts that can be transplanted into easily grown host organisms such as yeast to brew the compound in bioreactors, without heavy chemical synthesis. The fiber cap’s route, with its different enzymes and its built-in branch, widens that repertoire. It is a reminder that the search for sustainable ways to produce medicines often begins with a basic-science question about how, and why, nature learned to make them in the first place.

Frequently asked questions

What is psilocybin?

Psilocybin is the main psychoactive natural product of so-called magic mushrooms. In the body it is converted to psilocin, which alters consciousness by acting on serotonin receptors in the brain. It is built from the amino acid L-tryptophan.

Which mushrooms make psilocybin?

The best-known producers belong to the genus Psilocybe, but the compound has also been found in Gymnopilus, Panaeolus, Pluteus and certain Inocybe fiber caps, as well as in the cicada-parasitizing fungus Massospora.

What did the 2025 study actually discover?

It showed that the fiber cap Inocybe corydalina builds psilocybin using a completely different set of enzymes from Psilocybe, arranged in a different order. This provided biochemical proof that psilocybin biosynthesis evolved at least twice, independently, within the mushrooms.

What does it mean that psilocybin evolved twice?

It is an example of convergent evolution: two unrelated lineages arriving at the same end product by separate routes. The two pathways share no chemical reactions and use unrelated enzymes, yet both produce identical psilocybin.

How do the two pathways differ?

They run several steps in the opposite order. Psilocybe removes a carboxyl group before adding oxygen; the fiber cap adds oxygen first. The later methylation and phosphate-adding steps are also reversed. Remarkably, both routes still pass through a single shared intermediate, 4-hydroxytryptamine.

What is baeocystin, and why does it matter here?

Baeocystin is a close chemical relative of psilocybin. In Psilocybe it is a precursor on the way to psilocybin, but in the fiber cap it is a finished end product in its own right, because that pathway forks. This is why fiber caps often contain as much baeocystin as psilocybin.

Do scientists know why mushrooms make psilocybin?

Not yet. The leading hypotheses involve defense, such as deterring or altering the behaviour of animals that eat the mushrooms, but the study is explicit that the true ecological reason remains unknown.

Why does this discovery matter for medicine?

Psilocybin is being studied as a treatment for therapy-resistant depression. Mapping additional natural pathways expands the toolkit of enzymes that can be transferred into host organisms like yeast, making it possible to produce the compound sustainably in bioreactors rather than by complex chemical synthesis.