The present study compares the mycorrhizal communities associated with 36 populations of Struthiopteris spicant L. Weiss across Europe and the United States, following an ITS-focused metabarcoding approach and analyzing geographical and environmental factors. This fern species exhibits a great tolerance to variations in light, nutrient, and pH conditions, and has been observed with and without mycorrhizae. Our study explores in deep for the first time facultative mycorrhization in a single fern species and it was complemented by a previous greenhouse experiment with 80 specimens of S. spicant and three factors (Light, Phosphorus, and Nitrogen).