Fossils and ferns in the resolution of land plant phylogeny

Fifty-two taxa of living and extinct vascular plants were evaluated in an u nconstrained numerical cladistic analysis using 101 morphological character s to simultaneously resolve the phylogenetic relationships of ferns sensu l ate. Included in the analysis were ferns assignable to the Cladoxylales, St auropteridales, Rhacophytales, Zygopteridales, Ophioglossales, Marattiales, Filicales, and Hydropteridales, as well as a rhyniophyte, a trimerophyte, equisetophytes, lignophytes, and the psilotophytes Psilotum and Tmesipteris . The results placed ferns and fernlike plants in three distinct clades, in dicating that ferns s.l. are a polyphyletic grade group. Fern clades consis t of extinct stauropterids; extinct cladoxylaleans, rhacophytaleans, and zy gopteridaleans; and eusporangiates and leptosporangiates with living and ex tinct species. Psilotophytes occur near the base of the tree rather than ne sting with the Filicales, as hypothesized by some. These results place Ophi oglossales as the sister group to Marattiales plus the leptosporangiates, s upporting the hypothesis that Ophioglossales represent ferns rather than pr ogymnosperms. These analyses are a first attempt, which includes extinct pl ants, to develop cladistic hypotheses for the overall topology of fern phyl ogeny and to lay the groundwork for more detailed analyses of relationships among the homosporous leptosporangiates.