Most people never think twice about symbiotic life-forms like this orange lichen, in which the plant and fungi kingdoms work together to thrive. But such liaisons are everywhere. Most plants -- from rice to redwoods -- harbor fungal partners. Biologist François Lutzoni and colleagues inferred the relationships among species in each kingdom as its members diverged over one billion years. They found that many of the major events in one kingdom, such as the leap to land, coincided with a new symbiotic pairing or a surge of species in the other. “Their respective evolutionary histories are deeply interconnected,” researchers report.