In a Chinese forest, researchers have discovered a fungus that can grow up to 50 centimeters tall and weigh 2.2 kilograms.
At first glance, it does not look like the usual mushroom with a stem and cap. Instead, it forms a large upright mass, sometimes branched, covered in a yellowish fibrous substance. People in some regions of Yunnan, in southwestern China, were already familiar with this strange organism. But scientists have only just given it a name: Dianjunus rex, or “D-rex.”
Excerpt from Tintin's album The Shooting Star, by Hergé
Its size is not its only point of interest. In fungi, what we see at the surface is only part of the organism: the part that serves in particular to produce and disperse spores, tiny elements capable of giving rise to other fungi. The rest develops mainly in wood or soil.
In Dianjunus rex, however, this visible part reaches exceptional dimensions for its broader family, the ascomycetes. This group includes morels, truffles and many much smaller fungi. The researchers estimate that the structures observed are the largest ever described in this group.
To determine which species this giant was related to, the team compared its DNA with that of many other fungi. The result came as a surprise: it did not match any known family. The scientists therefore propose creating a new family, called Dianjunaceae, to accommodate this species.
Panel (a) shows several yellow-white, finger-shaped fungi emerging from a decomposing tree stump surrounded by green vegetation.
Panels (b) to (h) show groups or isolated fungi of similar color and shape growing in various forest-soil environments, some partially covered by soil or leaves.
Panel (i) shows several cleaned fungal specimens, brown in color, on a digital scale, highlighting their irregular, root-like shapes.
By tracing its evolutionary history, they also estimated that this lineage appeared approximately 65 million years ago. This was just after the mass extinction that marked the disappearance of non-avian dinosaurs.
The study provides another intriguing detail. Compared with several related species, the fungus's genome contains relatively few genes involved in producing substances that break down wood. The researchers still need to understand precisely how it feeds in the forests where it grows, particularly near roots and decomposing wood.
This discovery is a reminder that even very large organisms can remain unknown to scientists for a long time, and that by studying a living fungus, we can sometimes trace a history that began when the dinosaurs had just disappeared.