Firefungus
(Mycoignis sessilis) A slowly growing subterranean fungus which lives on damp surfaces in tunnels and underground crawlways. Firefungus glows a soft yellow-green or pure green in the dark, similar to the color of Omphalotus nidiformus, the "ghost fungus". (The number of known members of this family of fungi is steadily increasing: the newest are described here and here.)
Firefungus serves as a food source (and, when heavily grown, as a shelter or hiding place) for many small creatures in underground habitats, such as hidebehinds, skinwings and dun mice. The chemical which causes the bioluminescence of the firefungus has an affinity with retinal tissue, so that the eyes of creatures which have fed on firefungus usually glow in the dark for a prolonged period after feeding. (SYWTBAW)
See also: SUBTERRANEAN ECOLOGIES: WIZARDLY FLORA (NORTH AMERICA / EUROPE).