Taphrina polystichi is an ascomycete fungus that parasitizes Christmas fern (Polystichum acrostichoides) in eastern North America.

Mix notes that the fungus was originally identified as Exoascus filicinus by Coker,[1] though this is not listed as a synonym of the species.

[3] However, the authors described a new species based on the strains of T. polystichi and T. virginica in a later study using molecular phylogenetics and physiology, but they did not synonymize the taxa.

[5] In trials of carbon utilization, T. polystichi was able to use dextrose, sucrose, maltose, melezitose, trehalose, dextrin, inulin, and mannitol.

The ability to use mannitol and the inability to use xylose and succinic acid distinguished it from the other species tested.