This figure is taken from Pryer et al. (2001). The tree was generated from comparisons between 3 chloroplast data sets (rbcL, atpB, and rps4) and one nuclear SSU rRNA data set. The tree illustrates three monophyletic clades of vascular plants: the lycopods, the seed plants, and the ferns + horsetails. The analysis shows that the psilophytes and horsetails are firmly embedded within the fern taxa.