Fungi make up one of life's kingdoms - as broad and busy a category as animals or plants. Microscopic yeasts are fungi, as are the sprawling networks of honey fungi, or Armillaria, which are among the largest organisms in the world. The current record holder, in Oregon, weighs hundreds of tons, spills across ten square kilometers, and is somewhere between two thousand and eight thousand years old. There are probably many larger, older specimens that remain undiscovered. Many of the most dramatic events on Earth have been - and continue to be - a result of fungal activity. Plants only made it out of the water around five hundred million years ago because of their collaboration with fungi, which served as their root systems for tens of million years until plants could evolve their own. Today, more than ninety percent of plants depend on mycorrhizal fungi which can link trees in shared networks sometimes referred to as the wood wide web. This ancient association gave rise to all recognizable life on land, the future of which depends on the continued ability of plants and fungi to form healthy relationships.