Omphalotus japonicus, commonly known as the tsukiyotake (月夜茸), is an orange to brown-colored gilled mushroom native to Japan and Eastern Asia. It is a member of the cosmopolitan genus Omphalotus, the members of which have bioluminescent fruit bodies which glow in darkness. A 2004 molecular study shows it to be most closely related to a clade composed of Omphalotus nidiformis of Australia, Omphalotus olivascens of Western North America and Omphalotus olearius of Europe.