This widespread northern (almost circumboreal) tetraploid (2n = 164) is derived from hybridization of intermedia and "semicristata"--a hypothetical species that may now be extinct (Cranfill 1980, FNA 2). Back crosses with intermedia are occasionally found; colls. from HARL (EKY), HENR (KY) and perhaps elsewhere (BELL MCRE, MORG, ROWA, WOLF) are referable to this hybrid. In Ky. carthusiana is widely scattered within seasonally damp woods on medium acid to fertile soils, but it is generally uncommon to rare. D. campyloptera Clarkson is a similar tetraploid of cool northeastern regions and high Appalachian summits that has been reported from Ky. (RAB) but not verified; its occurrence remains dubious (FNA 2). Both species have fronds that tend to die back during harsh winters, in contrast to the evergreen intermedia.