Chinese scientists discover “D-rex,” a giant fungus with roots stretching back 65 million years

Scientists exploring the forests of Yunnan, China, have discovered an extraordinary giant fungus that is challenging previous assumptions about how large certain fungi can grow. The newly identified species, Dianjunus rex, produces upright reproductive structures that can reach 50 cm (20 inches) in height and weigh as much as 2.2 kg (4.9 pounds). These are the largest known fruiting bodies among fungi belonging to the phylum Ascomycota.

"This remarkable species represents a new fungal family, Dianjunaceae, and provides a rare window into the evolution of extreme fungal body forms," said Dr Indunil C Senanayake, an associate professor at the Germplasm Bank of Wild Species of the Kunming Institute of Botany in China and corresponding author of the study, published in Frontiers in Fungal Biology.

Researchers from the Kunming Institute of Botany encountered the unusual fungus while surveying several forest environments in Yunnan. Their fieldwork included temperate coniferous forests near Damaidi and Yipinglang, along with tropical rainforest near Nanbang.

The team spotted unusually large, whitish reproductive structures, known as 'stromata', growing from the woody roots of Chinese cork oak trees. These structures emerged from the rhizosphere, the region of soil surrounding plant roots, and appeared to belong to an unidentified member of the ascomycete fungi.

Ascomycetes make up the largest major group of fungi, with more than 64,000 recognized species. Unlike familiar mushrooms, these fungi do not produce true mushroom structures. Instead, they generate spores within tiny sac-like structures found inside or on the surfaces of their fruiting bodies.

To investigate the discovery, the scientists collected samples and preserved reference specimens in the Kunming Institute of Botany's collections. They also cultivated spores under laboratory conditions to examine the fungus's physical characteristics and sequenced its genome, including its protein-coding genes.

The genetic analysis, together with a close examination of the fungus's physical features, revealed that the discovery represented much more than a previously unknown species. It was sufficiently different from known fungi to require the creation of a new genus and an entirely new family (Dianjunaceae) within the order Xylariales.

The researchers named the species Dianjunus rex, drawing inspiration from its impressive size and the ancient Dian kingdom. Its nickname, 'D-rex', reflects its exceptional stature among related fungi.

Its closest known relative is Graphostroma platystoma, a fungus that grows on dead hardwood throughout the Northern Hemisphere. That species is the sole representative of its own family, Graphostromataceae.

Members of the order Xylariales are known for producing a variety of specialized chemical compounds and enzymes capable of breaking down complex molecules in plants. Researchers believe similar enzymes may allow 'D-rex' to decompose dead wood and obtain nutrients from it.

Using a technique known as a 'molecular clock', the scientists compared the fungus's DNA with genomic information from hundreds of other fungi whose evolutionary histories have been established. This analysis allowed them to estimate when the Dianjunaceae family first appeared.

Their results suggest that the lineage originated approximately 65 million years ago, roughly one million years after the Cretaceous-Paleogene mass extinction. That catastrophic event eliminated the non-avian dinosaurs along with countless other animal and plant species.

"This timing raises an intriguing possibility. After the mass extinction, forests experienced dramatic changes, including the sudden availability of large amounts of dead plant material," said Senanayake. "For wood-associated decomposing fungi, such environmental disruption may have created new ecological opportunities."

Before its discovery, the tallest known ascomycete fruiting bodies measured approximately 20 to 30 cm. The newly identified fungus can reach 50 cm, making it substantially taller than the previous record holders.

One possible explanation involves how the fungus releases and spreads its spores. By extending high above the forest floor, its reproductive structures may be better positioned to catch moving air and distribute spores through dense vegetation.

However, growing such a large structure also requires considerable energy. The researchers suggest that this unusual evolutionary strategy would be advantageous only in environments where the benefits of greater spore dispersal outweigh the resources needed for growth.

"A fruiting body which towers above surrounding vegetation and debris could have better dispersal of spores by wind in dense forests. However, such a large structure requires substantial energy investment, suggesting that this strategy likely evolved only where the ecological benefits outweighed the costs," hypothesized Senanayake.

Researchers believe the region is particularly well suited to the evolution of unusual fungal species because it contains a wide variety of habitats, has experienced relatively stable climatic conditions, and supports intricate relationships among living organisms.

Despite these favorable conditions, many fungi in the region have received little scientific attention. Remote and difficult terrain complicates fieldwork, while the seasonal appearance and often hidden nature of fungal reproductive structures make some species especially difficult to locate. Historically, research has also concentrated heavily on fungi with commercial or practical value.

"This region combines exceptional habitat heterogeneity, climatic stability, and complex biotic interactions that promote fungal diversification. Historically, however, fungal diversity in these ecosystems has been underestimated due to logistical difficulties in field sampling, the seasonal and cryptic nature of fungal fruiting, and a historical emphasis on economically important fungi," said Senanayake.