Fungi were one of the first life forms to appear on land. The first fungi likely grew as gigantic, tree-like prototaxites, which dominated Earth for over 40 million years before green algae emerged from the shallow seas and began to colonize the Earth’s surface. These green algae are the ancestors of all plants, but they would not have successfully survived without the help of fungal partners.

Fungi-plant partnerships take many forms. Fungi, bacteria, and algae can combine into lichens, which have existed for millions of years across huge swaths of the planet. Lichens can survive in extreme conditions and are often the only life forms found where others could not possibly grow. Mycorrhizal relationships, in which fungi inhabit the roots of land plants, began to occur as soon as roots appeared. These partnerships are beneficial to both plants and fungi, and form the basis for the huge underground networks known as the “wood wide web.” Roots themselves would likely not exist without fungi. Fungi’s ability to decompose nearly any organic structure created soil—a substance that the vast majority of root systems depend on for nutrients and stability. The ancient cooperation between plants and fungi likely guided the way that plants developed and allowed for the vast biodiversity seen throughout Earth’s history.