Elliptochloris, not Coccomyxa, is the photobiont of three lichenized Multiclavula species collected in Japan

Approximately 20,000 species of lichenized fungi have been described to date; however, the diversity of their photobionts remains poorly understood. In this study, photobionts were isolated and cultured from three Multiclavula species ( M. mucida , M. petricola , and M. vernalis ) collected in Japan, and identified using light microscopy, transmission electron microscopy, and molecular phylogenetic analyses. Previous studies have generally reported that the photobionts of Multiclavula belong to the genus Coccomyxa . In contrast, our results demonstrate that the photobiont of M. mucida is Elliptochloris subsphaerica , a conclusion further supported by successful thallus formation in co-culture experiments. The photobionts of M. petricola and M. vernalis were found to represent a previously undescribed species, which is described herein as Elliptochloris parasphaerica sp. nov. This study represents the first report of Elliptochloris as a photobiont of lichenized basidiomycetes. Phylogenetic analyses based on the rbc L dataset revealed that E. subsphaerica comprises several subclades. Notably, M. mucida preferentially associates with a particular subclade of E. subsphaerica , suggesting a degree of photobiont selectivity.