As the reign of the dinosaurs crumbled about 65 million years ago, new royalty rose from the ashes: a king among fungi.

Scientists recently identified Dianjunus rex, a gigantic species of fungus in what’s now China that shares part of its name with Tyrannosaurus rex, the renowned dinosaur “king.”D. rex belongs to a family of fungi that appeared following the extinction event that wiped out all non-avian dinosaurs, along with roughly 75% of all plant and animal life on Earth.

D. rex dwarfs its fellow fungi with its upright, pale yellowish reproductive structures, or fruiting bodies, called stromata that can grow to be 20 inches (50 centimeters) tall — about the height of an airplane carry-on suitcase — and weigh nearly 5 pounds (2.2 kilograms).

“It’s always interesting to hear about a new kind of fungus or mushroom species that is spectacular in size,” said Kabir Peay, a professor of biology and Earth system science at Stanford University in California, who was not involved in the new research. “It helps point to all of the really exotic forms of fungal life on this planet that haven’t had a chance to be described by science.”Scientists recorded D. rex in forests in southwestern China’s Yunnan province during fungal diversity surveys conducted in 2024 and 2025. The findings were reported September 28 in the journal Frontiers in Fungal Biology.

Farmers in the region had previously seen the fungus’ fleshy fingerlike stromata clustered around a dead tree. While the giant fungus has not been tested for toxins, some locals had even tasted it and reported no ill effects, said study coauthor Indunil Senanayake, an associate professor at the Kunming Institute of Botany in China.

“However, no one noticed it as an important thing,” Senanayake told CNN in an email. But when a curious local sent photos of the peculiar fungus to the scientists, the researchers quickly realized they were looking at something special.

The new study describing D. rex draws attention to how much there is yet to discover about biodiversity in fungi.

The mass extinction that caused the dinosaurs’ demise may have created an environment for the king-size fungus to evolve and thrive, according to the study. Not only was D. rex a newly discovered species — it belonged to a unique family of fungi. Through genetic analysis and comparisons with other fungi, researchers found that the new family, named Dianjunaceae, likelyemergedabout 1 million years after the asteroid impact that ended the Cretaceous Period (145 million to 66 million years ago).

“During this event, photosynthesis was suppressed, and huge quantities of dead leaves, wood, roots, and carcasses accumulated,” Senanayake said. At a time when other forms of life struggled to survive, decomposers such as fungi that consumed dead organic matter could exploit that banquet.

In size, D. rex doesn’tnearly measure up to T. rex, but it does tower over other fungi. This speciesis the largest known in the phylum Ascomycota, which is the most diverse group of fungi and contains about 65,000 species, including morels, truffles and yeasts.

Before D. rex’s discovery, the largest known member of Ascomycota was a bulbous brown fungus in Kenya called Engleromyces goetzei, which has a diameter of nearly 12 inches (30 centimeters) and weight of around 7 pounds (3.2 kilograms), Senanayake said. All other ascomycetes, also known as sac fungi, that are close relatives of D. rex range from microscopic to just a few inches tall.

One question the scientists want to answer next is why D. rex is so large compared with other fungi in its phylum, Senanayake said.

“Generally, ascomycetes do not produce large stromata, as it is an energy waste,” she explained.

Sac fungi reproduce by actively expelling their spores; in D. rex, the upper part of the fruiting bodies contains thousands of tiny spore-releasing pores. However, the forest floor of its habitats is densely covered with fibrous plant material that may trap spores, Senanayake said.

D. rex’s fruiting body rises high above the forest floor, which may allow spores to disperse more widely and improve reproductive success, she suggested.

Fungi are essential organisms that contribute to Earth’s carbon cycle and support the health and nutrition of many plant species.

“It’s really important that we understand what they do,” Stanford’s Peay said. “The first step in understanding what they do is describing them, acknowledging their existence, and then later trying to understand more details about their ecology.”Scientists have described around 150,000 species of fungi to date, but some estimates indicate there are between 2 million and 13 million species on the planet.

“It’s a vastly underappreciated and underdescribed group of organisms,” Peay added.

Fungi can be surprisingly difficult to spot in their forest habitats, even specimens as large as D. rex. A fungus is largely made up of threadlike filaments called hyphae, known collectively as a mycelium. These tendrils typically are buried in soil, decaying wood or vegetation, with the reproductive bits — the stromata — popping above the ground “when the environmental conditions are right, or the fungus comes to the end of its life cycle,” Peay explained.

These features make discovering a new fungus often a matter of being in the right place at the right time. Otherwise, “even really impressive mushrooms like this can go undescribed or unnoticed,” he said, referring to D. rex.

Mindy Weisberger is a science writer and media producer whose work has appeared in Live Science, Scientific American and How It Works magazine. She is the author of “Rise of the Zombie Bugs: The Surprising Science of Parasitic Mind-Control” (Hopkins Press).