Bisporella citrina, commonly known as yellow fairy cups or lemon discos, is a species of fungus in the family Helotiaceae. The fungus produces tiny yellow cups up to 3 mm (0.12 in) in diameter, often without stalks, that fruit in groups or dense clusters on decaying deciduous wood that has lost its bark. The widely distributed species is found in Australia, North Africa, Asia, Europe, North America, and Central and South America. Found in late summer and autumn, the fungus is fairly common, but is easily overlooked owing to its small size. There are several similar species that can in most cases be distinguished by differences in colour, morphology, or substrate. Microscopically, B. citrina can be distinguished from these lookalikes by its elliptical spores, which have a central partition, and an oil drop at each end.