These include 13 extant homosporous filicaleans, 17 extinct homosporous and heterosporous ferns from Paleozoic strata, five extant and one extinct heterosporous leptosporangiate ferns, two extant marattiaceous ferns, two extant ophioglossaceous ferns, one extant and two extinct equisetophytes, both extant homosporous psilotophytes (i.e., Psilotum and Tmesipteris), one extinct heterosporous progymnosperm, three extinct and one extant seed plants, and the extinct homosporous trimerophyte Psilophyton crenulatum (Appendix 1).
In Fern Clade #1 the homosporous species Stauropteris oldhamia is sister to the heterosporous species Gillesplea randolphensis + Stauropteris burntislandica.
A polytomy at the next node consists of Osmunda + Schizaea + the Permian species Skaaripteris minuta + a clade that consists of several Carboniferous fossil taxa + a clade that includes the heterosporous Hydropteridales + several living genera of Filicales.
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 recent discovery that heterosporous leptosporangiate ferns (i.e., Hydropteridales in [ILLUSTRATION FOR FIGURES 2-4 OMITTED]) form a monophyletic group nested within the filicaleans (Hasebe et al., 1994, 1995; Rothwell & Stockey, 1994; Pryer et al., 1995; Stevenson & Loconte, 1996) provides a benchmark for resolving relationships within the leptosporangiate clade.
in reconstructing the cladistics of heterosporous ferns.