Michael G. Simpson 2010. Plant Systematics. Cap.5 Evolution and diversity of woody and seed plants.
helsinki.fi
helda.helsinki.fi
Christenhusz, M.J.M, Reveal, J.L, Farjon, A., Gardner, M.F, Mill, R.R, y Chase, M.W. 2011. A new classification and linear sequence of extant gymnosperms. Phytotaxa 19: 55-70. (pdf)
Braukmann, T.W.A.; Kuzmina, M.; and Stefanovic, S. (2009). "Loss of all plastid nhd genes in Gnetales and conifers: extent and evolutionary significance for the seed plant phylogeny". Current Genetics 55 (3): 323–337. doi:10.1007/s00294-009-0249-7. PMID 19449185.