Mycena cystidiosa is a species of mushroom in the family Mycenaceae. Described as new to science in 1964, it is known only from New Zealand and Australia. The fruit bodies have a broadly conical small white cap up to 12 mm (0.5 in) wide, with distantly spaced cream-coloured gills on the underside. The stipe is particularly long, up to 20 cm (8 in), with an abundant covering of white hairs at the base. The species is known for its abundant rhizomorphs—long, root-like extensions of mycelia.