The Federally threatened Eastern Prairie Fringed Orchid, Platanthera leucophaea (Nutt.) Lindley (Orchidaceae), has experienced long-term decline largely due to habitat loss and degradation. Although this species has been propagated from seed in the laboratory, achieving seedling survival ex vitro has been problematic, forcing conservationists to sow seeds directly into field sites in an attempt to generate seedlings. Given that the mycorrhizal fungi needed for germination in situ have sporadic distributions, sowing seeds of this threatened species indiscriminately is not a preferable option. Thus, locating fungal “hotspots” using seed baits, and amending soil with fungi may have practical merit. In anticipation of the latter possibility, we provide a comprehensive list of the 75 mycorrhizal fungi isolated from P. leucophaea protocorms, seedlings and mature plants during the past 10 y from sites in Illinois and Michigan, including newly acquired strains from five additional sites in Illinois. Collectively, 66 of the 75 isolates (88%) were assignable to the anamorphic form-genus Ceratorhiza, including all of the fungi recovered from the five additional sites. This further supports the hypothesis that P. leucophaea relies primarily on Ceratorhiza to fulfill its initial and long-term mycotrophic needs. Although Ceratorhiza appears to be an ubiquitous associate of P. leucophaea, it should not be assumed that specific strains of this genus are equally widespread. Thus, we advocate that the fungi used in conservation should be limited to strains acquired from the same or nearby populations.