Likewise, placement of Marattiales in the current results [ILLUSTRATION FOR FIGURES 2 & 4 OMITTED] as sister group to the leptosporangiate Filicales + Hydropteridales agrees with traditional systematic interpretations (Gifford & Foster, 1989).
Traditional classifications of leptosporangiate ferns recognized several families of apparently primitive filicaleans ("basal" filicaleans in this analysis), two or more families of more highly derived Filicales ("derived" filicaleans in this analysis), and two groups of heterosporous water ferns (Gifford & Foster, 1989).
The monophyletic Hydropteridales occurs as sister group to the derived Filicales [ILLUSTRATION FOR FIGURES 2 & 4 OMITTED] at a node in the midregion of the leptosporangiate tree.
Although there is a growing consensus that leptosporangiate ferns form a clade in which the monophyletic Hydropteridales is embedded within the paraphyletic Filicales, the disparity of results from recent phylogenetic analyses [ILLUSTRATION FOR FIGURE 5 OMITTED] emphasizes that familial circumscriptions and relationships among filicalean families remain incompletely resolved.
The hypothesis that Psilotum and Tmesipteris are closely related to the Filicales (Bierhorst, 1968, 1971, 1977) is not supported by the results of the current analyses.
The "leptosporangiate" ferns form a clade that includes the Filicales plus the Hydropteridales.
Within the "leptosporangiate" clade the Hydropteridales is monophyletic and is nested within the Filicales, which is a paraphyletic grade group.