Record-Size Fungus From China Defines New Family Estimated to Date to Dinosaur Extinction

Researchers in China have described a giant fungus that they say is the largest of its kind. Its whitish reproductive structures can reach about 50 centimeters, or roughly 20 inches, in height, and the fungus weighs nearly five pounds. Nicknamed "D-rex," it has been formally named Dianjunus rex. It belongs to a newly created fungal family, and the researchers estimate that the family's lineage emerged about 65 million years ago, shortly after the extinction of the non-avian dinosaurs. The work was published in Frontiers in Fungal Biology.

Scientists from the Kunming Institute of Botany came across the fungus while surveying forests in China's Yunnan region. Their fieldwork covered temperate coniferous forests near Damaidi and Yipinglang, as well as tropical rainforest near Nanbang. There, they spotted unusually large reproductive structures, called stromata, growing from the woody roots of Chinese cork oak trees. The structures emerged from the rhizosphere, the soil zone surrounding plant roots, and appeared to belong to an unidentified member of the ascomycetes.

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

To work out what they had found, the team collected samples and preserved reference specimens in the institute's collections. They also grew the fungus's spores in the laboratory to examine its physical characteristics, and they sequenced its genome, including its protein-coding genes.

The genetic and physical evidence together showed that the fungus was more than a new species. According to the researchers, it was different enough from known fungi to require a new genus and an entirely new family, Dianjunaceae, within the order Xylariales. The name draws on the fungus's size and on the ancient Dian kingdom. Its closest known relative is Graphostroma platystoma, which grows on dead hardwood across the Northern Hemisphere and is the only member of its own family, Graphostromataceae.

Members of Xylariales are known for making a range of specialized chemical compounds and enzymes that can break down complex plant molecules. The researchers believe similar enzymes may let D-rex decompose dead wood and draw nutrients from it.

To estimate the family's age, the team used a technique called a molecular clock. They compared the fungus's DNA with genomic data from hundreds of other fungi whose evolutionary histories are established. The analysis suggests the Dianjunaceae lineage arose about 65 million years ago, roughly one million years after the Cretaceous-Paleogene mass extinction, the catastrophe that wiped out the non-avian dinosaurs along with countless other species.

The researchers see the timing as suggestive. "After the mass extinction, forests experienced dramatic changes, including the sudden availability of large amounts of dead plant material," said Dr Indunil C Senanayake, corresponding author of the study and an associate professor at the Germplasm Bank of Wild Species of the Kunming Institute of Botany. "For wood-associated decomposing fungi, such environmental disruption may have created new ecological opportunities."

The fungus's size is a separate puzzle. Before this discovery, the tallest known ascomycete fruiting bodies measured about 20 to 30 centimeters. D-rex can reach 50. One possible explanation concerns spore dispersal: a structure that rises high above the forest floor may catch moving air better and spread spores through dense vegetation. But building something so large takes considerable energy. "Such a large structure requires substantial energy investment, suggesting that this strategy likely evolved only where the ecological benefits outweighed the costs," Senanayake hypothesized.

The finding also points to how much remains unknown about fungi in the region. The researchers say China's subtropical forests offer a wide variety of habitats, relatively stable climate and intricate relationships among living organisms, all of which can promote fungal diversification. Yet fungal diversity there has been underestimated. Remote, difficult terrain complicates fieldwork, fungal fruiting is seasonal and often hidden, and research has historically focused on fungi with commercial value. "The discovery illustrates how much fungus biodiversity remains to be discovered in East Asian forests," Senanayake said.

Several points in the work remain hypotheses. The link between the lineage's origin and the post-extinction world is framed as a possibility, not a demonstrated cause. The researchers' explanations for the fungus's height, spore dispersal balanced against energy cost, are likewise proposals. The role of wood-degrading enzymes in D-rex is something the researchers believe, based on its relatives, rather than a result reported here. The scientists expect that continued exploration of these forests will turn up more species, and possibly more unexpected forms and evolutionary histories.