Plants and fungi have formed mycorrhizal relationships since the early days of prehistory. The most primitive form - vesicular-arbuscular mycorrhiza - arose in the Devonian era, when multicellular terrestrial plants first came into being. In fact, it was this very relationship between plant and fungi that enabled plants to colonize land over 400 million years ago. This relationship continued with the early vascular plants, and progressed to ectomycorrhiza in the Middle Cretaceous period as plants evolved to become the woodland giants we know today. Indeed, given the intimate relationship between these unlikely partners, the rise of large trees may never have come about had the first plant and fungus never found each other.