A survey of mycobionts of federally threatened Platanthera praeclara (Orchidaceae)

Terrestrial orchids require mycobionts for critical nutritional support during germination and growth. Despite the importance of such fungi, little is known of their identity and ecological roles. In the United States, the destruction of midwestern prairie ecosystems has resulted in the decline of the native Platanthera praeclara Sheviak and Bowles and its associated mycobionts. Mycobionts of P. praeclara from six populations across Minnesota and Missouri were isolated from protocorms and mature plants and were identified to the genus level. Hyphal morphology, colony appearance, rate of growth, and monilioid cell morphology including septal pore ultrastructure were examined to characterize the isolates. Results indicate that P. praeclara is primarily associated with Ceratorhiza isolates at various growth stages. Few Epulorhiza isolates were recovered from roots and protocorms indicating this genus may be less critical for the orchid. Worldwide, Epulorhiza have been documented as orchid mycobionts more frequently but species of Ceratorhiza seem to be more prevalent in the North American prairie ecosystems. Preservation of prairies with special attention to conserving mycobionts of P. praeclara is needed if viable populations of both organisms are to persist.