Most plants obtain at least some nutrients through hyphae of mycorrhizal fungi, and these symbioses appear to date back to the early days of plants' land colonization. Since then, several mycorrhizal types have evolved, each type allowing exploitation of different nutrient pools and habitats, yet limiting the symbionts' ranges to areas of mutual occurrence. As mycorrhizae play important roles in community and ecosystem ecology, understanding the evolution of different mycorrhizal states allows researchers to connect plant evolution, community and ecosystem ecology. Recent substantial advances in our understanding of plant phylogeny and mycorrhizae in general prompted a re-evaluation of previously published reports. We mapped available mycorrhizal data onto current phylogenetic models of the plant kingdom. The resulting trees show some interesting patterns, such as a concentration of ectomycorrhizae in the Eurosids, and they also reveal significant gaps in our knowledge. These trees, overlays, and evolutionary commentary are available on the web (http://www.wisc.edu/botit/MPP/Index.htm) to provide a practical tool for teaching about mycorrhizae to systematists and ecologists of all levels. These comparative data also provide suggestions for future research leading to elucidation of the biological mechanisms underlying evolution of these symbioses.

Key words: mycorrhizae, plant ecology, plant phylogeny