If we're talking about the largest single organism by mass, it's a fungus:
* Armillaria ostoyae (also known as honey mushroom or "Humongous Fungus") is a massive honey mushroom that covers over 8.9 square kilometers (2,200 acres) in Malheur National Forest, Oregon. It's estimated to weigh over 605 tons and be at least 2,400 years old.
However, if we're looking at the largest organism by area covered, it's a plant:
* Pando is a clonal colony of quaking aspen trees in Utah, covering over 106 acres (43 hectares). It's estimated to be 80,000 years old and is connected by a single root system, making it essentially one massive organism.
There are other contenders for the title of "largest organism," depending on your criteria:
* Posidonia oceanica (Mediterranean seagrass) forms vast underwater meadows that can stretch for miles.
* Coral reefs are formed by colonies of tiny animals called coral polyps and can span huge areas.
Ultimately, determining the "world's largest organism" is a matter of definition and perspective. Each of these examples represents incredible feats of natural scale and interconnectedness.
