Giant Mushroom Reveals New Fungal Family Dating To Dinosaurs’ Extinction

Nearly 5-Pound Fungus Adds a Whole New Branch to the Fungal Family Tree

A fungus pushing up from the roots of dying trees in southwestern China can grow 20 inches long, counting the stalk buried in soil, and weigh close to 5 pounds, about as much as a bag of flour. Size is only part of the oddity. DNA tests show it fits into no known fungal family, and its lineage appears to date to roughly the time the dinosaurs died out.

Researchers in China collected five specimens from rainforest and mountain forest sites in Yunnan Province over two summers, then named the species Dianjunus rex and placed it in a brand-new family, Dianjunaceae. Their report appears in Frontiers in Fungal Biology. The genus name nods to the Dian Kingdom, a historical society in the region, and rex is Latin for king.

Timing is the other surprise. By comparing genetic data across fungal species, the team estimated that the family’s lineage emerged about 65 million years ago, with a margin of error stretching from 50 to 80 million years ago. That range straddles the mass extinction that wiped out an estimated 75% of all plant and animal species. The authors propose the family may have taken advantage of new openings as forests recovered, an idea the dates alone cannot confirm.

DNA Tests Place the Giant Fungus in a New Fungal Family

Dianjunus rex belongs to Xylariales, a large group of fungi, many of which recycle dead wood and plant material and keep carbon moving through forests. Others live quietly inside healthy plants. Giants are rare in the group. A two-lobed relative on bamboo in Kenya weighed about 7 pounds, heavier than the Yunnan fungus. Members of this group also make natural compounds that interest biotechnology researchers, though the paper does not test this species for any.

Appearance sets the new species apart as well. Its finger-like branches are pale to dark yellow, while most of its look-alikes are black. Fresh specimens are very fleshy and dry out quickly once picked. Specimens from the tropical rainforest grew larger than those from subtropical sites.

To work out where it belongs, the team photographed the fungus where it grew, studied its structure under microscopes, and grew cultures from its spores in the lab. They then read four stretches of its DNA and compared them with 202 related fungal strains in public databases. They also sequenced most of the DNA of three specimens, capturing roughly 96% of the core genes expected in fungi of this kind.

Every method pointed the same way, even when the team repeated the analysis with a second set of genes. The new samples formed their own branch of the fungal family tree, sitting next to a known family yet clearly separate, with the strongest statistical support possible. Physical traits backed up the DNA, including a powdery yellow coating that set the new family apart from others in its group.

To date that branch, the team compared genes shared across 66 fungal samples, using known split dates from other well-studied fungi as reference points. Splits between fungal families are commonly dated to between 50 and 150 million years ago, so 65 million falls within a typical range.

Giant Fungus Carries Far Fewer Plant-Digesting Genes

Wood-rotting fungi rely on enzymes, proteins that chop tough plant material into pieces small enough to eat. When researchers counted its genes for this enzyme toolkit, Dianjunus rex had about 220, roughly half or fewer of the 420 to 640 found in related wood-rotting fungi, the steepest drop among all the fungi compared.

Genes for cutting up pectin, a compound that helps hold plant cell walls together, were nearly absent, numbering zero or one versus 7 to 19 in close relatives. Pectin fragments can also trigger a living plant’s immune system, a reaction a fungus with few such genes may largely avoid. Genes for building the fungus’s own cell walls, meanwhile, made up an unusually large share of its enzyme-related genes, roughly a quarter.

Researchers describe a working hypothesis: the fungus may live inside plants without harming them, then start feeding and sprouting mushroom-like growths once the host dies. Every growth in the study came from dying or decaying trees or the soil around their roots, which fits that idea, though the study did not test the lifestyle directly. Spending less on costly digestive enzymes, the authors reason, could leave more energy for building such a giant structure.

This New Fungal Family May Be One of Many Hidden in Yunnan

More than 6,000 fungal species have been documented in Yunnan Province, yet the authors say the true total could exceed 100,000. They argue that continued fieldwork paired with DNA analysis is how hidden lineages like this one will be found. Oversized fruiting growths have also evolved independently in other fungal lineages, including truffle-forming ones, the paper adds.

A fungus that can weigh as much as a bag of flour went unclassified in a region already known for its fungal diversity. If something that big was hiding, smaller surprises are likely waiting in those forests.

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