Abstract: Epulorhiza inquilina sp. nov. is described from the mycorrhizas of mature plants of Platanthera clavellata, P. cristata and P. integrilabia, coexisting terrestrial orchids native to bogs in the southern Appalachians. The new taxon was isolated consistently and exclusively from these orchid taxa over a seven-year period. Protocorms from seeds of P. integrilabia planted in their native habitat were also colonized by E. inquilina and consequently some specificity in the symbiosis is suspected. E. inquilina is binucleate and has imperforate parenthesomes but differs from other species in the genus because of its woolly colonial morphology, tan colour on artificial media, and its elongate monilioid cells that develop in relatively short chains. The five species of Epulorhiza are distinguished in a key