A new naturally occurring fern hybrid between Cystopteris X tennesseensis and C. tenuis is described from plants collected in Fairfield County, Ohio. This new hybrid is interesting for three reasons. First, although most of the spores are aborted, some large unreduced spore mother cells are regularly produced and these apparently account for the hybrid’s abundance at the site. Second, observations of the hybrid’s chromosomes at early meiotic metaphase show approximately 42 bivalents and 84 univalents. This chromosome pairing behavior supports the morphological evidence that the C. tenuis parent is an autotetraploid. Third, this is the first sterile primary Cystopteris hybrid known from living plants.