High specificity generally characterizes mycorrhizal association in rare lady's slipper orchids, genusCypripedium.

Lady's slipper orchids (Cypripediumspp.) are rare terrestrial plants that grow throughout the temperate Northern Hemisphere. Like all orchids, they require mycorrhizal fungi for germination and seedling nutrition. The nutritional relationships of adultCypripediummycorrhizae are unclear; however,Cypripediumdistribution may be limited by mycorrhizal specificity, whether this specificity occurs only during the seedling stage or carries on into adulthood. We attempted to identify the primary mycorrhizal symbionts for 100Cypripediumplants, and successfully did so with twoCypripedium calceolus, 10Cypripedium californicum, sixCypripedium candidum, 16Cypripedium fasciculatum, twoCypripedium guttatum, 12Cypripedium montanum, and 11Cypripedium parviflorumplants from a total of 44 populations in Europe and North America, yielding fungal nuclear large subunit and mitochondrial large subunit sequence and RFLP (restriction fragment length polymorphism) data for 59 plants. Because orchid mycorrhizal fungi are typically observed without fruiting structures, we assessed fungal identity through direct PCR (polymerase chain reaction) amplification of fungal genes from mycorrhizally colonized root tissue. Phylogenetic analysis revealed that the great majority ofCypripediummycorrhizal fungi are members of narrow clades within the fungal family Tulasnellaceae. Rarely occurring root endophytes include members of the Sebacinaceae, Ceratobasidiaceae, and the ascomycetous genus,Phialophora.C. californicumwas the only orchid species with apparently low specificity, as it associated with tulasnelloid, ceratobasidioid, and sebacinoid fungi in roughly equal proportion. Our results add support to the growing literature showing that high specificity is not limited to nonphotosynthetic plants, but also occurs in photosynthetic ones. [ABSTRACT FROM AUTHOR]