A previously unrecognized interspecific hybrid in the fern genus Polypodium is described from collections made at a single remote locality in central Arizona. Originally identified as P. glycyrrhiza, this sterile nothotaxon is easily distinguished from other members of the genus and is here named Polypodium ×aztecum Windham & Yatsk. The hybrid is tetraploid, exhibiting ca 37 bivalents and 74 univalents at diakinesis. Based on geographic proximity and shared morphological traits, we conclude that P. hesperium is one of the parents of the new taxon. Assuming that the hybrid is more or less intermediate between P. hesperium and a second parental taxon, we attempt to identify the missing parent. The most likely candidate is P. calirhiza, a species of Oregon, California, and Mexico that has not been documented from Arizona. However, we cannot rule out the possibility that the missing parent is an as yet unidentified member of the P. plesiosorum complex from Mexico.