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.

Omphalotus is a genus of basidiomycete mushroom, in the family Omphalotaceae, formally circumscribed by Victor Fayod in 1889. Members have the traditional cap and stem structure. They are saprobic, and fruit in clumps on the ground, adjacent to host trees. The best known and type species is the jack-o'-lantern mushroom (Omphalotus olearius). Species of Omphalotus have been mistaken for chanterelles. All Omphalotus species are presumed poisonous, causing gastrointestinal symptoms. Some Omphalotus species have bioluminescent properties.