Nicholas Jacobson, Peter Jacobson, Ernst van Jaarsveld, Kathryn Jacobson: Field evidence from Namibia does not support the designation of Angolan and Namibian subspecies of Welwitschia mirabilis Hook. In: Transactions of the Royal Society of South Africa, Volume 69, Issue 3, 2014, S. 179–186. doi:10.1080/0035919X.2014.950187 10.1080/0035919X.2014.950187.
google.com.pe
books.google.com.pe
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.