Elliptochloris, Not Coccomyxa, is the Photobiont of Three Lichenized Multiclavula Species in Japan

The photobionts of lichenized basidiomycetes remain poorly understood compared with those of many lichenized ascomycetes. In this study, we investigated the photobionts of three Japanese species of Multiclavula—M. mucida, M. petricola, and M. vernalis—using culture isolation, light microscopy, transmission electron microscopy, molecular phylogenetic analyses, ITS2 secondary structure comparisons, and co-culture experiments. Photobiont cells within the thalli possessed pyrenoids, excluding Coccomyxa as the primary photobiont of the examined specimens. Cultured photobionts were morphologically and ultrastructurally consistent with Elliptochloris, and phylogenetic analyses of 18S rDNA, ITS, and rbcL datasets placed all isolates within or near the E. subsphaerica–E. marina complex. The photobionts of M. mucida were assigned to E. subsphaerica subsp. subsphaerica, and co-culture experiments with the corresponding fungal isolate successfully resynthesized globular lichenized thalli. In contrast, isolates from M. petricola and M. vernalis formed a distinct lineage, supported by ITS and rbcL phylogenies, ITS2 sequence divergence, and hemi-CBCs. This lineage is described here as E. subsphaerica subsp. subalpina subsp. nov.