Mycorrhizal fungal associations of the fringed orchids (Platanthera) in the US, inter- and intra-species variation.

Abstract

Understanding which orchid mycorrhizal fungi (OMF) are needed to support orchid growth is critical for their conservation. We used DNA sequencing and network analysis of OMF collections from the North American Orchid Conservation Center, along with published sequences, to compare the OMF associated with 28 species and 4 natural hybrids in the genus Platanthera. We found that relatedness of orchid species was generally a poor predictor of OMF associates. However, species in sections Fimbriata and Blephariglottis that co-occurred and formed natural hybrids associated with multiple fungi that were completely shared among co-occurring species. Differences in mycorrhizal associates within species mapped onto orchid genetic differences that distinguished geographic regions (mountains vs. coast vs. inland, not strictly geographic distance). Orchids that were specialized or moderately specialized in their OMF associations required relatively few samples to describe the bulk of their associated OMF, while generalized orchids required considerably more samples to describe their associated OMF. These results provide insight into species differences in mycorrhizal associations and can be used to guide management actions, as well as providing a foundation for future research.

Supplementary information: The online version contains supplementary material available at 10.1007/s10531-025-03233-4.