Which mushroom is reputed to be the largest living organism on Earth?

Honey Fungus

The Honey Fungus, located in the Malheur National Forest in Oregon, spans over 3.4 square miles (8.8 km²) and is estimated to be about 2,400 years old. This colossal organism is actually a network of fungal filaments underground called mycelium. Its impressive size and age demonstrate the remarkable ability of fungi to survive and thrive in diverse conditions, making this organism a fascinating subject for biologists and mycologists.