Scientists surveying forests in China’s Yunnan province have identified a giant fungus whose upright reproductive structures can grow to 50 centimeters (20 inches) tall and weigh as much as 2.2 kilograms (4.9 pounds). Named Dianjunus rex, the species produces the largest known fruiting bodies among fungi in the phylum Ascomycota and is distinct enough to require the creation of a new genus and family.
“This remarkable species represents a new fungal family, Dianjunaceae, and provides a valuable window into the evolution of extreme fungal body morphology,” said Dr. Indunil C. Senanayake, associate professor at the Wild Species Germplasm Bank at the Kunming Botanical Research Institute in China and corresponding author of the study published in Frontiers of fungal biology.
“This discovery shows how much fungal biodiversity remains undiscovered in East Asian forests.”
A giant fungus hidden in China’s forests
Researchers from the Kunming Institute of Botany encountered the rare fungus while surveying several forest environments in Yunnan province. Their fieldwork included temperate coniferous forests near Damaidi and Yipinglan, as well as tropical rainforest near Nanbang.
The scientists found an unusually large, whitish reproductive structure, known as a stroma, growing from the base of a Chinese cork oak tree. The structures emerged from the rhizosphere—the area of soil surrounding plant roots—and appeared to belong to an unidentified member of the ascomycete group.
Ascomycetes are 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 form spores inside small, sac-like structures located within or on the surface of their fruiting bodies.
The scientists collected samples and preserved reference specimens in the Kunming Botanical Research Institute’s collection. They also cultivated spores under laboratory conditions to examine the fungus’s physical characteristics and sequenced its genome, including its protein-coding genes.
Introducing Dianjunus rex
Genetic analysis and detailed examination of the fungus’s physical characteristics showed that it was more than a previously unknown species. It differed sufficiently from known fungi that the researchers established 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 kingdom of Dyan. Its nickname, “D-rex,” reflects its exceptional stature among closely related fungi.
Its closest known relative is Graphostroma platystoma, a fungus that grows on dead hardwood trees in the Northern Hemisphere. That species is the only representative of its family, Graphostromataceae.
Members of the order Xylariales produce a variety of specialized compounds and enzymes capable of breaking down complex molecules in plants. The researchers believe similar enzymes may allow D-rex to decompose dead wood and obtain nutrients from it.
A 65-million-year evolutionary connection
One of the most notable findings concerns the newly identified family’s ancient evolutionary origin.
Using a technique known as a molecular clock, the scientists compared the fungus’s DNA with genomic information from hundreds of other fungi with established evolutionary histories. This analysis allowed them to estimate when the lineage leading to Dianjunaceae first appeared.
The results suggest that the lineage arose about 65 million years ago, approximately 1 million years after the Cretaceous–Paleogene mass extinction. That catastrophe eliminated the non-avian dinosaurs along with countless other plant and animal species.
The timing raises the possibility that major environmental changes following the extinction created favorable conditions for the unusual fungal ancestor.
“This timing poses an interesting possibility: After the mass extinction, forests experienced dramatic changes, with large amounts of dead plant material suddenly becoming available,” Senanayake said. “Such environmental disruption may have created new ecological opportunities for wood-associated decomposers.”
Why does the fungus grow so large?
Another unanswered question is how and why Dianjunus rex evolved its unusual size.
Before its discovery, the tallest known ascomycete fruiting bodies were approximately 20 to 30 centimeters high. The newly identified fungus can reach 50 centimeters, making it considerably taller than the previous record holder.
One possible explanation involves the way the fungus releases and disperses 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, producing such large structures requires considerable energy. The researchers suggest that this strategy would be advantageous only in environments where improved spore dispersal provides greater benefits than the resources required for growth.
“Fruiting bodies towering above surrounding vegetation and debris may be better able to disseminate spores by wind in dense forests. However, such large structures require significant energy investment, suggesting that this strategy is likely to have evolved only when the ecological benefits outweighed the costs,” Senanayake hypothesized.
More undiscovered fungi may live in China’s forests
The discovery highlights how much remains unknown about fungal diversity in China’s subtropical forests.
Researchers believe the region is particularly well suited to the evolution of rare fungal species because it contains a wide range of habitats, has relatively stable climatic conditions and supports complex relationships among organisms.
Despite these favorable conditions, many fungi in the region have received little scientific attention. Remote locations and difficult terrain make fieldwork challenging, while the seasonal appearance and hidden nature of fungal reproductive structures can make some species especially difficult to find. Historically, research has also focused on fungi with commercial or practical value.
Scientists hope that continued exploration of these forests will reveal additional species, along with more unexpected forms and evolutionary histories.
“This region combines exceptional habitat heterogeneity, climatic stability, and complex biotic interactions that drive 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 the historical emphasis on economically important fungi,” Senanayake said.
Source: www.sciencedaily.com
