Field, KJ, JR Leake, S Tille, KE Allinson, WR Rimington, MI Bidartondo, DJ Beerling, and DD Cameron, From mycoheterotrophy to mutualism: mycorrhizal specificity and   functioning in Ophioglossum vulgatum sporophytes. New Phytologist 205:1492-502 (2015). doi:10.1111/nph.13263