Rhopographus filicinus forms stromata under the epidermis of bracken.  The stromata are often confluent and form conspicuous lines of black crusts, several centimetres long, on the dead stems of Bracken. 

Several other species form black crusts or spots on dead bracken stems, usually much smaller the Bracken Map.  In some cases, microscopic examination may be needed.  

host

Photograph the fungus on the bracken; note the host species in your comments.  

Bracken

Autumn and Winter.

"Incertae sedis" is used when a species has not been assigned to a Family in the taxonomic hierarchy.