Armillaria ostoyae, widely known as the largest fungus in the world when it was discovered in Oregon in 1998, stretches 3.5 miles (5.6 km) across. It looks similar to a mushroom, but it is only a distant relative. The largest mushroom fungi is Fomitiporia ellipsoidea, which measured about 32 feet (10 m) long and 2.6 feet (80 cm) wide and weighed about 1,100 pounds (about 500 kg). It is technically the largest fruiting body, or spore-producing structure, and was discovered in 2010 in China underneath a tree. It is a shelf or bracket fungus, which means that the fungus attaches itself to wood or other materials and develops in a shelf-like shape.
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