Heaviest organism

The heaviest living "being" on Earth is a single gigantic specimen of Armillaria ostoyae honey mushroom, discovered in the Malheur National Forest of Oregon, USA, which is estimated to weigh somewhere between 7,500 and 35,000 US tons (6,800–31,750 tonnes). Known colloquially as the "Humongous Fungus", it occupies a total area of 965 hectares (2,385 acres), equivalent to 1,350 soccer fields, also making it the largest fungus by area.

Its estimated weight surpasses that of Pando, a network of quaking aspen (Populus tremuloides) growing in the Wasatch Mountains of Utah, USA, which remains the world's most massive plant. The clonal forest, comprised of around 47,000 individual stems, was confirmed in December 1992 to be a single root system, covering 43 ha (106 acres) and weighing an estimated 6,000 tonnes (6,600 US tons). The clonal system is genetically uniform and acts as a single organism, with all the component trees (part of the willow family) changing colour or shedding leaves in unison.

The honey mushroom is well known for its glowing surface, caused by bioluminescent bacteria, although most of its tissue is around 1 m (3 ft) underground, in the form of root-like mycelia. This also makes it the largest bioluminescent organism on the planet.

Its age is calculated to be at least 2,400 years old, but it may, in fact, be as old as 8,650 years.

The largest living organism by area, meanwhile, is a specimen of Posidonia australis seagrass (aka Poseidon’s ribbon weed) located in Shark Bay off Western Australia, covering approximately 200 km2 (77 sq mi) – equivalent to around 28,000 soccer fields or more than 450 times bigger than Vatican City, the world's smallest country. The superlative seagrass meadow was described in Proceedings of the Royal Society B on 1 June 2022.