The megatree is the GBOTB.extended.WP.tre megatree reported by Jin and Qian (2022). It included the megatree of seed plants reported by Smith and Brown (2018) and the pteridophyte part of the megatree reported by Zanne et al. (2014).
Jin, Y. & Qian, H. (2022) V.PhyloMaker2: An updated and enlarged R package that can generate very large phylogenies for vascular plants. Plant Diversity, 44, 335-339. Smith, S.A., Brown, J.W., 2018. Constructing a broadly inclusive seed plant phylogeny. Am. J. Bot. 105, 302-314. Zanne, A.E., Tank, D.C., Cornwell, W.K., et al., 2014. Three keys to the radiation of angiosperms into freezing environments. Nature 506, 89-92.