The world's largest living organisms might be hiding under your feet

Nature · Published 20 October 2026 · Updated 21 October 2026 Swipe more like this →

In short: While we marvel at giant sequoias, a silent, subterranean titan may hold the record for the largest living thing on Earth. The honey fungus creates massive underground mats, some spanning hundreds of acres, capable of surviving forest fires and outliving centuries of history by consuming entire forests from the roots up.

The genus Armillaria consists of about 35 species of parasitic fungi, primarily found in the forests of northern North America and Europe. These fungi are renowned for their ability to form extensive underground networks called mycelium. These networks grow via rhizomorphs—hardy, cordlike bundles of threadlike filaments that secrete enzymes to digest wood and living tree roots. Because they are shielded underground, these rhizomorphs are incredibly resilient, capable of withstanding extreme temperatures and even surviving aboveground forest fires.

The sheer scale of these organisms is staggering. In 1992, a specimen of A. bulbosa in Michigan was identified as a single mycelium mat covering more than 15 hectares (37 acres), with an estimated weight exceeding 10,000 kg (22,000 pounds). It was estimated to be at least 1,500 years old. However, a later discovery of A. ostoyae on Mount Adams in Washington state revealed an even larger specimen covering approximately 607 hectares (1,500 acres), with an estimated age of 400 to 1,000 years.

For gardeners and foresters, Armillaria is a formidable foe known as honey fungus. UK garden landscapes suffer from this fungus, which is the deadliest disease for various herbaceous and woody perennials. It causes 'white rot' by decaying roots and wood, often leading to the sudden death of plants during hot, dry weather. Because there are no chemical controls, management requires physical intervention: excavating and destroying infected material or installing deep physical barriers like butyl rubber strips to block the rhizomorphs' path.

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