Cytogenetic evidence from experimental hybrids is presented to show that Asplenium haussknechtii, a widespread fern of Asia Minor, is an allotetraploid species which has originated from hybridization between the two diploid species, A. aegaeum and A. ruta-muraria subsp. dolomiticum. The morphology of the three species is consistent with this hypothesis. Cytogenetic evidence from other experimental hybrids indicates that A. creticum, a fern endemic to Crete, is also allotetraploid, sharing one parent with A. haussknechtii and having A. viride as its second parent. Morphological evidence confirms that A. creticum is most likely to have arisen from hybridization between A. viride and A. aegaeum. Elucidation of the parentage of these two species means that the evolutionary origins of all the tetraploid species of Asplenium known from continental Europe have now been determined. The origins of these species and the development of the Asplenium flora of Crete are discussed in relation to the Pleistocene glaciations.