Polyphlebium tenuissimum, synonym Trichomanes tenuissimum, is a species of fern in the family Hymenophyllaceae. It is endemic to Ecuador. In 2006, in a taxonomic revision of the family Hymenophyllaceae, Ebihara et al. assigned this species to the genus Polyphlebium rather than Trichomanes. However the combination does not appear to have been formally published; hence the "comb. ined." (combinatio inedita) in the Checklist of Ferns and Lycophytes of the World.