Polypodium appalachianum is a common member of the Polypodium vulgare species complex in eastern North America. It is a diploid progenitor of Polypodium virginianum, with which it co-occurs and is frequently confused. It can be differentiated from that species by its acute (vs. obtuse) pinna apices, lamina that is broadest at the base (vs. the middle) and concolorous brown (vs. brown with a dark central stripe) rhizome scales. Like most other Polypodium species, it is most commonly found on rocks; it prefers more acidic rocks than P. virginianum.