This is based on Christenhusz et al.: A linear sequence of extant families and genera of lycophytes and ferns (2011)[2] and Rai and Graham: Monilophyte Phylogeny (2010)[3] Note that Equisetaceae branches first, and the Lindsaeaoid families are different than in the previous phylogram.
The following phylogram shows a likely relationship between the other vascular plant classes and the leptosporangiate ferns.[4] Note that these relationships are far from settled. For example, this diagram shows Equisetopsida as a sister to Polypodiopsida. Depending on how the data was interpreted (e.g. using Parsimony vs. maximum-likelihood analyses), Equisetopsida could just as well have been placed a sister to a Marattiopsida/Polypodiopsida clade.[4]
While it is generally accepted that the leptosporangiate ferns are monophyletic, it is considered to be likely that the eusporangiate ferns, as a group, are polyphyletic. As shown in the examples from three recently published phylograms in the following table, it can be seen that the four eusporangiate fern families do not form a single clade.
^ abLehtonen (2011) Samuli Lehtonen: Towards Resolving the Complete Fern Tree of Life. PLoS ONE 6(10): e24851. doi:10.1371/journal.pone.0024851 (13 Oct 2011)
^Kathleen M. Pryer & Eric Schuettpelz (2009). "Ferns"(PDF). In S. Blair Hedges & Sudhir Kumar (ed.). The Timetree of Life. Oxford Biology.
