Deciphering interfungal relationships in the 410Â million-year-old Rhynie chert: Glomoid spores under attack

Various types of other fungi colonize glomeromycotinan (Mucoromycota) spores in the Early Devonian Rhynie chert. However, relatively few of these associations have been described and evaluated in detail. One particular type of glomoid spore located in degrading land plant axes from the Rhynie chert provides evidence of (simultaneous) interaction with three different fungi. Massive callosities occur around the intrusion filaments of a chytrid-like parasite with epibiotic sporangia, while the hyphae of a delicate mycelial fungus extend into the spore lumen without triggering a recognizable host response. Several spores show large numbers of inwardly directed projections, which are regularly distributed and consist of a short hyphal branch encased in host wall material. The projections represent the penetration sites of a distinctive, mycelial fungus that forms a mantle-like hyphal sheath around the spores. This type of fungal interaction with glomeromycotinan spores has not previously been reported, and thus expands our knowledge of the numerous interfungal relationships that existed in early continental ecosystems.