Sometimes new species evade detection because they’re tiny and thus easy to miss—not this giant fungus. Shaped like a hand reaching out of the ground, this new species of fungus was discovered deep in the forest in China’s Yunnan Province. A research team from the Kunming Institute of Botany, part of the Chinese Academy of Sciences, reported it as a new species they named Dianjunus rex.

The name comes from the region’s ancient Dian Kingdom and the Chinese pronunciation of the word “fungus.” D. rex is a type of Ascomycete, which is the largest phylum of fungi with over 64,000 known species, and among them, this new fungus produces the largest masses of mushroom recorded. Unlike what we typically think of as a “mushroom,” Ascomycetes don’t form caps and stems but produce structures called fruiting bodies, which release spores to reproduce. And growing up to 20 inches and weighting nearly five pounds, D. rex’s are huge.

Within the Ascomycetes, the giant fungus constitutes an entirely new biological family (the broader classification of genus and species), meaning that it has no close relatives—at least that we know of. While 6,000 fungal species have been documented in Yunnan, mycologists believe the province known for its biological diversity could easily harbor 100,000

“The discovery illustrates how much fungus biodiversity remains to be discovered in East Asian forests,” Indunil C. Senanayake, an associate professor at the Kunming Institute of Botany and the lead author of the paper, said in a press release.

Senanayake and his research team conducted surveys in the Nanban tropical rainforest, where they came across large, whitish fruiting bodies growing in the soil near the roots of dying trees. They documented and collected fungi growing in a wide variety of shapes like cylinders, spindles, and cupped palms. The fruiting bodies appeared to develop finger-like branches upon maturity. They found that the above-ground portions are covered with white, powdery fibers that turn dark yellow as the fungi mature while the portions buried in the soil are black and smooth.

The fruiting bodies dried rapidly when the scientists took samples back to the lab. They found that the interiors were dense and sponge-like, appearing white or yellow with no strong odor or taste. (Don’t try this experiment at home.)

Analyzing the DNA of these fungi, the researchers reconstructed a “molecular clock,” which revealed that D. rex diverged from other species approximately 65 million years ago. This is the end of the Cretaceous period, immediately following the mass extinction that is believed to have wiped out three quarters of all plant and animal species, including the dinosaurs. That means D. rex and T. rex never met, but this era was likely a boon for fungi. Large quantities of dead plant material became available following the die off, which could have provided new ecological opportunities for fungi and other organisms that decompose such matter.

Genomic analyses, however, indicated that D. rex doesn’t have nearly as many decomposition-related genes as the scientists expected. Compared to some of its closest relatives that also feast on plant matter, the huge fungus has only about half the usual number of decomposition-related genes.

Senanayake has a theory about this. Though, so far, they have only found the fruiting bodies around dying plants, the fungus may be leading a “double life”—living inside healthy trees and then feeding on dead plant material when the hosts die. That could perhaps explain how D. rex is able to store enough energy to build the massive fruiting bodies.

This is just a theory for now, but the giant fungi undoubtedly do need a surplus of energy to grow so large. Senanayake hypothesizes that the benefit of these large fruiting bodies is that they tower higher than the surrounding plants and fallen leaves, which could be advantageous for wind-mediated spore dispersal in a dense forest. “However, such a large structure requires substantial energy investment, suggesting that this strategy likely evolved only where the ecological benefits outweighed the costs.”

This story was originally published in WIRED Japan and has been translated from Japanese.