While blue whales or towering redwood trees often come to mind as Earth’s largest living organisms, the true title, based on specific scientific criteria, belongs to a less visible contender. These well-known examples certainly hold impressive records in their categories.
The Humongous Fungus
The organism widely recognized as the largest by area, and arguably by mass, is Armillaria ostoyae, commonly known as the Humongous Fungus. This fungus spreads through a vast underground network of mycelia, or rhizomorphs, which absorb nutrients from soil and decaying wood.
A notable Armillaria ostoyae specimen in Oregon’s Malheur National Forest covers an estimated 2,385 acres (965 hectares). Scientists estimate its age between 2,000 and 8,000 years, making it one of the oldest known organisms. Its immense size is measured by mapping its interconnected underground network, not by a single, visible mushroom.
Defining Immense Size
The concept of “biggest” in biology is not a single measurement, but depends on specific criteria. Scientists define size using various metrics, including mass (total weight), volume (the amount of space an organism occupies), length (its longest dimension), and area (the total surface or ground covered). An organism might be the largest by one measure but not by another, leading to different record-holders for different categories.
Armillaria ostoyae holds its record based on the vast area its interconnected mycelial network occupies underground. Its estimated mass, while difficult to ascertain precisely, is thought to be hundreds of tons, potentially making it the heaviest organism. This distributed growth pattern contrasts sharply with organisms that have a single, consolidated body. Understanding these distinct measurement criteria helps clarify why different organisms can claim “biggest” titles under varying definitions.
Other Record-Breaking Organisms
While the Humongous Fungus holds the record for the largest continuous organism by area, other living things achieve impressive sizes in different ways. The blue whale (Balaenoptera musculus) is the largest animal on Earth, both by mass and length. An adult blue whale can reach lengths of up to 98 feet (30 meters) and weigh over 190 tons (172,365 kilograms), making it the heaviest animal to have ever lived. Its immense size allows it to efficiently filter-feed on vast quantities of krill in the ocean.
Among trees, the Giant Sequoia (Sequoiadendron giganteum) is recognized as the largest single organism by volume. Specifically, the “General Sherman Tree” in California’s Sequoia National Park contains an estimated volume of 52,508 cubic feet (1,487 cubic meters) of wood. While not the tallest tree, its sheer girth and immense trunk contribute to its unparalleled volume.
Another remarkable contender for large size is the Pando aspen clone in Utah, a vast grove of genetically identical quaking aspen trees (Populus tremuloides). Pando is considered a single organism because all its stems originate from a single, interconnected root system. This clonal colony spans approximately 106 acres (43 hectares) and is estimated to weigh around 6,600 tons (6 million kilograms), making it the largest known organism by mass for a clonal colony. Unlike the Armillaria fungus, which is a single individual spreading underground, Pando consists of thousands of individual stems connected by a shared root system.