When Star Trek: Discovery hit screens and streaming in 2017, it brought incredible visuals, updated storytelling, and a deepening lore to the Star Trek universe. While it played with the backstories of known characters and tweaked the designs of certain species (both highly polarizing among fans), Discovery also brought us new technology and new aliens, including the first sentient fungal species in canon. The jahSepp were only around for a few episodes, but these fungi were not only complex and beautifully fleshed out but also expertly built, incorporating our current mycology knowledge base.
In season 1 of Discovery, we see the series’ namesake ship traveling instantaneously along the mycelial network. Anywhere the network exists (which we learn in season 4 ends just shy of the Galactic Barrier), Paul Stamets—an astromycologist named after the actual present-day mycologist—can jump the ship and its complement from point A to point B using Prototaxites stellaviatori, a fictional species inspired by an extinct giant fungal genus from about 400 million years ago (Cottier 2026). Season 2, however, went one step further for us fungiphiles, introducing the jahSepp, a species of sentient fungus that lived within the multidimensional mycelial network.
We’re first introduced to the jahSepp unknowingly. Earnest and awkward Ensign Sylvia Tilly unexpectedly encounters May Ahearn, an old friend from junior high school who’s new to the Discovery crew. May shows up in a turbolift, in the corridor, on the bridge. Tilly quickly realizes, however, that no one else can see May, and a quick search of the Federation database reveals the May she knew died years ago. What started as annoying interactions quickly turn terrifying—not-May won’t leave Tilly alone, and after the entire bridge crew witnesses Tilly yelling at someone seemingly not there, Captain Pike orders her to sickbay.
May’s haunting of Tilly goes from mental to physical when it’s discovered that Tilly is infested by a fungal eukaryote, and the organism will not let her go despite numerous extraction methods. Eventually, the organism begins speaking through her in a moment reminiscent of The Exorcist. Quite the introduction to these new aliens in Trek.
While humanity has yet to encounter mushrooms that can communicate with or through us, it’s not out of the realm of what we can imagine fungal capabilities to be. Studies on mushroom communication are still in their infancy, but we know that different types of fungus have the ability to respond to and elicit favorable responses from other species. Mycorrhizal fungi share food and water with plants in mutualistic relationships. Parasitic fungi modify plants via growth regulators. Truffle mushrooms mimic animal sex pheromones to attract mammals and insects that then facilitate the spreading of spores (Halloway & Arévalo 2023). These may seem far from using a human as a puppet to speak words, but the chemical and electrical responses share similarities to neural activity in the brain (Wright 2025).
The jahSepp certainly knew what chemicals to release to get Engineers Paul Stamets and Jett Reno to do what they wanted. In order to facilitate the abduction of Tilly into the mycelial network, they dose Stamets and Reno with psilocybin, inducing a bad trip for the two while creating a fungal pod to transport Tilly in. This is the first bit of redirection we see in the narrative about the jahSepp, providing a moment of comic relief between the harrowing scene of Reno drilling into Tilly’s skull and Tilly disappearing with nothing but the human-sized fungal sack left behind.
The change in tone continues in the following scene where we quickly meet up with Tilly surrounded by waves of blue, pink, and purple cylindrical mushroom stalks. May Ahearn soon appears again, assuring Tilly that she brought her here, having transported her into the interdimensional mycelial network.
We’re never told a taxonomy of the jahSepp, but given their propensity for kidnapping, they might be genetically related to their Earth-bound cousins. Many species of terrestrial mushrooms set poison traps for insects, including the delicious oyster mushrooms (Pleurotus ostreatus). Some of these traps aren’t just chemical, either. At least twelve known species physically squeeze their prey to death. While insects and nematodes aren’t these mushrooms’ primary source of nutrients, they utilize these methods when deficient of certain nutrients, such as protein (Frazer 2021). Similarly, the jahSepp’s kidnapping of Tilly was due to dire circumstances; May and her people needed help. Everything that had transpired with her aboard the Discovery had been a misunderstanding.
Granted, it was a big misunderstanding that involved inducing hallucinations, infection, brain surgery, and abduction; however, May quickly explains to Tilly that her species is being destroyed by a monster, and she needs Tilly’s help to prevent their genocide. The ends justify the means, right? How else were the jahSepp going to get help from Tilly? You can’t really blame a mushroom for subpar communication skills in a time of crisis.
As the jahSepp’s story arc comes to a climax, they pull off their final feat that puts them in the god-like camp of Q or the Genesis Device: They resurrect Dr. Hugh Culber. In season 1 of Discovery, Dr. Culber—Paul Stamets’s partner—was brutally murdered at the hands of a Klingon double agent. After the USS Discovery arrives in the mycelial network to rescue Tilly, Stamets begins seeing Hugh and follows him. At first thinking he’s a hallucination—which makes sense given Paul’s bad trip not that long prior—he soon realizes that it’s actually the Hugh from their universe. He was transported into the mycelial network at the time of his death by the stellaviatori spores lingering on Paul. (The mechanics of this are a whole other essay, and plenty of those have been written.) Hugh is the monster the jahSepp have been scared of; he’s been inadvertently killing them in self-defense as they tried to do what fungi do: recycle his organic matter. The jahSepp are reluctant but, being the benevolent species they are, agree to let him go. However, as Hugh tries to leave the mycelial network, they discover that he can’t. His body has been reconstituted in the network; he can’t take it with him back out.
They all look to May. If the jahSepp could transport Tilly there, if they constructed Hugh’s body in the network and the pod on Discovery, couldn’t they do the same for Hugh’s body back in their home dimension? May is doubtful but promises to try, and after returning, the sack used to transport Tilly breaks down, revealing an alive and re-formed Hugh Culber inside.
This must be where Star Trek puts the fiction in “science fiction,” right? Not exactly. Fans familiar with The Last of Us know the Cordyceps genus well. This group of fungi, along with those in the genus Ophiocordyceps, have the ability to control the body of their hosts after infecting them. These fungi, of which we know about 750 species, are considered “zombie fungi” for how they change the behavior and ultimately re-animate their victims (Shersby 2025). This isn’t exactly resurrection, but animating corpses isn’t too many steps away. It might only be a matter of time and evolution for our myco-friends to add that ability to their already loaded arsenal.
“Saints of Imperfection” in season 2 of Star Trek: Discovery is the last time we see or hear from the jahSepp, but in the episode, May Ahearn and Sylvia Tilly pinky promise that they’ll see each other again. Sadly, in the next three seasons of the show, which ended after season five in 2024, that promise isn’t fulfilled. It’s too bad, too: These multi-dimensional (in more ways than one) aliens embodied what great science fiction can do—taking our current understanding of the world and extrapolating on where it could go. Maybe someday Tilly and May will be reconnected, or other jahSepp will be back on our screens, but until then, we’ll just have to forage for their inspirational cousins.
Bibliography
Cottier, Cody. Sarah Lewin Frasier, ed. “Mysterious tower fossils may come from a newly discovered kind of life,” Scientific American. 21 January 2026. https://www.scientificamerican.com/article/mystery-prototaxites-tower-fossils-may-represent-a-newly-discovered-kind-of/
Frazer, Jennifer. “How a Carnivorous Mushroom Poisons Its Prey.” Scientific American. 8 April 2021. https://www.scientificamerican.com/article/how-a-carnivorous-mushroom-poisons-its-prey/
Hathaway, Michael and Willoughby Arévalo. “How do fungi communicate?” MIT Technology Review. 24 April 2023. https://www.technologyreview.com/2023/04/24/1071363/fungi-fungus-communication-explainer
Shersby, Megan. “Cordyceps and Ophiocordyceps: the zombie fungi made famous by The Last of Us.” Discover Wildlife. 22 April 2025. https://www.discoverwildlife.com/plant-facts/fungi/cordyceps-ophicordyceps-zombie-fungus
Wright, Stephanie. Jacquie Leone, ed. “The Mycelium Revolution.” VitaRX. 28 May 2025. https://www.vitarx.co/resources/brain-memory-focus/the-mycelium-revolution
Editor: Gautam Bhatia.
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