What is the world's largest type of fungus by size?

The world's largest type of fungus by size is the Armillaria ostoyae, also known as the honey mushroom. It is a type of parasitic fungi that feeds on living and dead trees, and is found in North America and Europe. The fungus spreads through its mycelium, which is a network of thread-like structures that grow underground and can cover up to thousands of acres.

The Armillaria ostoyae can grow up to 3.5 miles (5.6 kilometers) across, making it the largest organism on Earth by area. Its size and longevity have also earned it the nickname of the 'Humongous Fungus'. The largest known specimen of the honey mushroom was found in the Malheur National Forest in Oregon, covering an area of about 2,200 acres (8.9 square kilometers).