Fungi of the family Psathyrellaceae are symbiotic partners of the mycoheterotrophic orchid Danxiaorchis yangii.

Fully mycoheterotrophic orchids rely entirely on fungal symbionts for carbon acquisition and are often highly specialized in their fungal associations. Danxiaorchis yangii is a fully mycoheterotrophic orchid species with an extremely limited population in its endemic region of southeastern China. Its fungal symbionts remain poorly understood. In this study, we investigated the fungal associations of D. yangii using both the isolation of culturable fungal endophytes and high-throughput sequencing of the ribosomal internal transcribed spacer-1 (ITS1) region. Six strains of Psathyrellaceae were isolated from rhizomes (underground stems) of D. yangii and phylogenetic analysis revealed that they belong to two main taxa. High-throughput sequencing further confirmed that the fungal community within the rhizomes was dominated by Psathyrellaceae. Moreover, an in vitro symbiotic seed germination assay demonstrated that one of the isolated strains could promote the growth of germinating seeds to the protocorm stage. These findings are significant for advancing our understanding of the mycoheterotrophic symbiosis in D. yangii.