Mycorrhizae regulate elemental and energy flows in terrestrial ecosystems. We understand much of how mycorrhizae work, but integrating all possible mechanisms into a whole has proven elusive. Multiple evolutionary events and the long evolutionary history mean that different plants and fungi bring independent characteristics to the symbiosis. This variety results in extensive physiological variation. How do we integrate functional responses with diversity to understand the role of mycorrhizae in ecosystems? We review ecophysiological mechanisms of mycorrhizae and organize these into functional groups. Species-area relationships are not curvilinear, but resemble the "broken stick" model. We coupled functional groups with a metacommunity analysis to show how complex behavior can be generated using a simple matrix model of resource exchange. This approach provides insights into how we might integrate diversity and function across landscapes.