The Hymenophyllaceae (Filmy-ferns) of which there are about 600 species worldwide have traditionally been divided into two main genera, Trichomanes and Hymenophyllum, with a few very morphologically distinctive taxa separated as discrete genera.
Molecular studies have helped us to understand the relationships within this group, in which there are few morphological characters to work with and in which various conflicting taxonomies have been suggested. It is now clear (Ebihara et al., 2007) that the c. 250 species of Trichomanes are better divided into 8 distinct genera. The Killarney fern thus becomes Vandenboschia speciosa. The genus Vandenboschia is among the most widespread occurring in both old and new worlds.
Killarney fern is an allotetraploid with 2n =144 chromosomes. Its diploid progenitors are not definitely known but from unpublished studies of the nuclear genome by Atsushi Ebihara in Tokyo, one is probably an as yet unnamed North American diploid (which has also given rise to the North American Vandenboschia boschiana), whereas the other possibly has a continental African origin and is a plant similar to V. gigantea.