“Ever since I since I was a graduate student, I wanted to do exactly the study that was just published,” says Anderson, who is now a professor of biology at the University of Toronto. Anderson contributed a couple of genomes for the study, but the bulk of the research and analysis was done by György Sipos and László Nagy, of the University of Sopron and the Hungarian Academy of Sciences, respectively.

Sipos and Nagy not only sequenced four species of Armillaria, but they also pinpointed genes active in the fungus’s rhizomorphs and mushrooms. To identify those genes, they had to figure out how to grow at least one species of Armillaria in a lab.

The rhizomorphs were the easy part. Once Armillaria took to their growing medium of rice, sawdust, tomato, and orange—“this fungus has really weird tastes,” notes Nagy—they spontaneously formed rhizomorphs. The mushrooms were much trickier. They had to trick the fungus into thinking it was autumn, which they did by moving their fungi to colder temperatures with progressively less light in Nagy’s lab. Sipos says his colleagues “did a really excellent job. It used to be be difficult to make this fungus produce the mushroom.” They succeeded in getting one species—Armillaria ostoyae, also the species of the giant Oregon fungus—to produce mushrooms.

All that trouble paid off though. When the team got the sequencing data back, they noticed that the same networks of genes appear to be active in both the fungus’s rhizomorphs and its mushrooms. It suggests one potential evolutionary origin for rhizomorphs in this genus: Armillaria could have gained its rhizomorphs—and consequently its ability to spread so wide—by co-opting genes originally used to grow mushrooms. Nagy speculates the rhizomorphs may be akin to mushroom stems that failed to sprout and grow a cap, instead growing long and thin underground.

The rise of Armillaria has come at the expense of trees. The fungus actually grows into trees and spread under the bark. At first they digest living wood and when they’ve done enough damage, they continue to feast on the dead wood. “You can basically see entire hills wiped out, entire forests wiped out,” says Nagy. You can’t see much of the humongous fungus in the Malheur Forest in Oregon since the Armillaria is mostly underground, but you can see all the trees it has killed.

Armillaria as a genus not a particularly picky eater either, and it attacks all sorts of plants. Understanding how the fungus spreads could impact many agricultural industries. For example, Kendra Baumgartner, a plant pathologist at the U.S. Department of Agriculture, studies Armillaria that specifically attack California vineyards. She was ecstatic to see the new study, which also catalogues the genomes, proteins, and active genes in Armillaria. “They generated an incredible amount of data,” she says. When we spoke last week, she told me she had the article’s official publication date marked on her calendar, so she could start digging through the data as soon as it’s out.