Dark taxon

In mycology, a dark taxon (: dark taxa; or dark fungus ) is a taxon that does not appear to produce any observable morphological structure and that appears impossible to cultivate in laboratory conditions. Dark taxa are chiefly detected by DNA sequencing, and in particular environmental metabarcoding.

Dark taxa make up a paraphyletic group, with dark taxa appearing in every major fungal lineage. Dark taxa appear to make up a significant portion of extant fungal taxa. According to "the majority of the extant fungal diversity produces no distinguishing morphological structures that are visible or describable", and according to Martin Ryberg dark fungi "could well prove to be the dominant life style in the fungal kingdom".

The naming of dark taxa is not supported by the ICN as a type specimen requires direct observation.