The largest single living organism on Earth is a "fungus" known as Armillaria ostoyae, commonly referred to as the honey fungus. This organism resides primarily underground in the Malheur National Forest in Oregon, USA. The massive fungal network covers approximately 2,385 acres and is estimated to be thousands of years old. The majority of the organism is made up of mycelium, which consists of thread-like structures that spread through the soil, decomposing organic matter. While not visible above ground, its fruiting bodies, which are the mushrooms, can appear seasonally, highlighting the organism's vast underground presence and its role in forest ecosystems.