MONOTROPES (Monotropoideae, Ericaceae) are achlorophyllous, epiparasitic plants that receive all of their fixed carbon from green plants through a common ectomycorrhizal association rather than by a direct parasitic connection (Fig. 1)(1,2). Using molecular identification methods we show that some monotropes are highly specific in their fungal associations and at least one species, Pterospora andromedea, is specialized on a single species group within the genus Rhizopogon. Phylogenetic analysis of the Monotropoideae shows that specialization has been derived through narrowing of fungal associations within the lineage containing P. andromedea. High specificity is contrary to past predictions for the Monotropoideae and for plant communities in general, raising many questions about the roles of mycorrhizal specificity in ecosystem function.