A review of symbiotic fungal endophytes in lycophytes and ferns – a global phylogenetic and ecological perspective

We present a review of the documented fungal colonizations of presumably symbiotic nature in lycophytes and ferns (“pteridophytes”). The sampling covers ca. 11 % (1287 spp.) of the estimated global diversity of these taxa (ca. 12,000 spp.) and shows an average presence of fungal endophytes of 68 %, which is significantly lower than the average presence of mycorrhiza of 80–85 % for the remaining tracheophytes. Above-average colonization rates up to 100 % among ferns are mainly found in phylogenetically old lineages, whereas below-average mycorrhization characterizes the Polypod I clade and the Aspleniaceae of the derived leptosporangiate ferns. Arbuscular Mycorrhizal Fungi (AMF) are found in 54 % of the species, to which 6 % of unspecified records of mycorrhizae should probably be added. Dark Septate Endophytes (DSE) are found in 13 % of the species, in about half the cases (6 %) together with AMF. Ectomycorrhizae have not been confirmed for pteridophytes so far, and basidiomycetes are found very rarely in mycoheterotropic gametophytes. Fungal endophytes are unevenly distributed across the life forms and most frequent with 75 % in the terrestrial species, followed with 69 % in saxicolous and with 58 % in epiphytic species. Although AMF have a low dispersal potential and thus are considered unreliable symbiotic partners for epiphytes, they are still present in 27 % of the investigated epiphytic pteridophytes. The occurrence of mycorrhizae across the taxa of pteridophytes bears a phylogenetic signal, as the derived ferns show a notable trend towards a growing independence from AM, in epiphytes more pronouncedly so than in terrestrial taxa.