Growing up to 50 centimeters tall and weighing nearly five pounds, the towering giant fungus Dianjunus rex forms a brand-new family, Dianjunaceae, whose evolutionary roots trace back approximately 65 million years to the aftermath of the asteroid impact that ended the age of dinosaurs.
Deep in the subtropical and temperate forests of southwestern China’s Yunnan province, a newly described fungus is challenging assumptions about how massive sac fungi can grow. Discovered during fieldwork conducted between August 2024 and July 2025. Dianjunus rex produces pale, fleshy, upright structures that emerge directly from the rhizosphere surrounding the woody roots of Chinese cork oak trees.
Most individual specimens recovered by scientists weighed between 250 and 600 grams. However, the largest recorded specimen tipped the scales at an astonishing 2.2 kilograms, standing up to 50 centimeters in total height. That exceptional scale shatters previous records for the phylum Ascomycota, where the tallest known fruiting bodies previously measured just 20 to 30 centimeters.
Field Discovery Across Yunnan Province
The path to describing the new organism began when a local resident sent photographs of the peculiar fungus to researchers at the Kunming Institute of Botany. Field surveys soon tracked the organism across distinct forest environments, ranging from temperate coniferous woods in Kunming and Lufeng to tropical rainforest habitats in Xishuangbanna Dai Autonomous Prefecture.
Jing Song collected initial specimens on August 5, 2024, near Damaidi village in Luquan County. According to study coauthor Dr. Indunil Senanayake, local farmers in the region had previously encountered the fleshy, finger-like clusters clustered around dead wood and even tasted them without reporting ill effects. Despite local familiarity, the organism had remained entirely unknown to formal science.
This remarkable species represents a new fungal family, Dianjunaceae, and provides a rare window into the evolution of extreme fungal body forms.
Dr. Indunil C. Senanayake, Kunming Institute of Botany
Genetic sequencing and morphological analysis confirmed that the find required establishing not just a new species and genus, but an entirely distinct family within the order Xylariales. Researchers chose the species name Dianjunus rex by combining the Chinese word for fungus with a reference to the ancient Dian kingdom. The species epithet honors its king-sized proportions.
Evolutionary Divergence Near the Cretaceous-Paleogene Boundary
To uncover the age of the lineage, the research team applied a molecular clock technique, comparing the fungus’s DNA against genomic datasets from hundreds of other fungal species. The analysis indicated that the family Dianjunaceae diverged from its closest known relatives approximately 65 million years ago.
That timeline places the evolutionary split coinciding with the Cretaceous–Paleogene extinction event that wiped out approximately 75 percent of plant and animal species, including the non-avian dinosaurs. While the dating calculations allow for a wider window between 50 million and 80 million years ago, investigators suggest that the cataclysmic die-off created sweeping environmental shifts.
Chinese researchers sampled specimens of a fungus that produces massive, upright stromata up to 50 cm in height and weighing up to 2.2 kg individually during mycological surveys in southwest China's Yunnan Province. The fungus is proposed as the new species Dianjunus rex gen. et… pic.twitter.com/72Zx9YJYLo
For wood-associated decomposing fungi, such environmental disruption may have created new ecological opportunities.
Dr. Indunil C. Senanayake, Kunming Institute of Botany
The sudden abundance of dead plant material across global forests likely opened fresh food sources and habitats, allowing ancient wood-decomposing lineages to adapt and thrive as ecosystems recovered.
Metabolic Trade-Offs Behind Towering Fruiting Bodies
Biologists remain puzzled by the immense energy investment required to support such a massive physical structure. Ascomycetes typically do not produce large stromata, as it is an energy waste.
However, the forest floors where Dianjunus rex grows are densely choked with low vegetation and leaf litter that can easily trap spores. By thrusting its fertile upper surfaces high above ground debris, the giant fungus gains a powerful aerodynamic advantage for wind-driven spore dispersal.
Genomic screening offered another potential clue regarding its survival strategy. The organism carries remarkably few genes dedicated to producing enzymes that break down plant tissue, a characteristic shared with some fungi that live harmlessly inside plants.
Scientists hypothesize that the fungus may spend part of its life cycle inside healthy trees. It may then feed on dead plant material after the host dies, husbanding its stored metabolic energy for the emergence of its towering reproductive pillars.