As is the case with most titles that end in “-est,” the competition for The World’s Largest Organism is fierce. The Great Barrier Reef certainly has its proponents, most of them Australian. There’s a stand of quaking aspens growing in Utah that’s a single clonal organism, rather than genetic individuals. If it does not merit the title of largest organism, it can at least claim to be the most Borg-like.

The real winner does not capture the popular imagination as much as a besieged coral or a forest of yellow-leafed trees: it is somewhat less scenic and probably won’t appear as the backdrop of an inspirational poster any time soon. It kills plants and lives underground, in Oregon. It is the humongous fungus, and we now have its genome.

Armillaria species—honey mushrooms—kill all kinds of plants. Conifers, ginkgos, grasses, and shrubs, in National Forests and in your backyard; all are susceptible. The fungus attacks its prey by sending out rhizomorphs, underground structures that leach onto the plant’s roots and kill them. Then it eats the dead woody tissue of its decomposing host.