Scientists have discovered what could be the largest and oldest living organism on earth -- an individual mightier than the blue whale, the giant sequoia tree or such past pretenders to size supremacy as the dinosaur.
The organism is a giant fungus, an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilized spore 1,500 to 10,000 years ago and now extending for more than 30 acres in the soil of a forest near Crystal Falls, Mich., along the Wisconsin border.
The fungus, called Armillaria bulbosa, is genetically uniform from one end of its expanse to the other, which is why scientists say it rightfully can be called a single individual.
They suggest it has possibly been growing since the end of the last Ice Age, making it older than any other known organism on earth. If all its mushrooms and tendrils are considered together, the fungus weighs about 100 tons, about as much as the more compact blue whale.
Dr. Myron L. Smith and Dr. James B. Anderson of the University of Toronto in Mississauga, Ontario, and Dr. Johann N. Bruhn of Michigan Technological University in Houghton report their discovery of the mammoth Armillaria in tomorrow's issue of the journal Nature.
The underground organism survives by feeding on dead wood and other detritus, spreading outward right beneath the surface as it senses the presence of nutrients nearby.
But scientists believe that the fungus has probably reached its maximum dimensions; at one, and possibly several, of its borders, the Armillaria is bumping against competing fungi, which are blocking the older giant's further colonization of the forest.
Researchers said the finding will force biologists to rethink their as sumptions about what constitutes an individual, a fundamental problem in the study of the natural world and its ecosystems.
Scientists normally view a single organism as something bound by a type of skin, whether of animal flesh or plant cellulose. But fungi, along with other organisms like coral and some types of grasses, grow as a network of cells and threadlike elements whose boundaries are not always clear.
Scientists said the new work was particularly significant because it used detailed genetic analysis, similar to the techniques of DNA fingerprinting, to prove that the 30-acre fungus was a discrete being, which had grown over the years by sending out clonal shoots of itself.
The new discovery also underscores the ubiquity and power of the planet's fungi, a kingdom of organisms quite distinct from the plant and animal kingdoms.
"Fungi are the base of all terrestrial ecosystems," said Dr. Thomas D. Bruns, an assistant professor of plant pathology and a fungal researcher at the University of California at Berkeley. "No ecosystem on the planet would continue to operate without fungi to decompose and recycle wood and plants."
But fungi are not always innocuous; they sometimes attack healthy tissue rather than being content with dead or dying material. A few virulent fungal species, like the Dutch elm pathogen, have managed to devastate entire populations of trees.
The scientists now believe that at some point in the distant past a fertilized spore, blown from a parent Armillaria mushroom, settled into the soil, germinated and extended reddish-brown rootlike rhizomorphs downward, seeking wood debris to feed on.
Eventually, the fungal webbing also began sprouting mushrooms to stretch above ground and disperse new fungal spores to the wind.