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Welwitschia
''Welwitschia'' is a monotypic gymnosperm genus, comprising solely the very distinct ''Welwitschia mirabilis''. The plant is commonly known simply as Welwitschia, and has various common names in local languages, for example ''kharos'' or ''khurub'' in Nama, ''tweeblaarkanniedood'' in Afrikaans, ''nyanka'' in Damara, and ''onyanga'' in Herero. It is the only genus of the family Welwitschiaceae and order Welwitschiales, in the division Gnetophyta. Informal sources commonly refer to the plant as a "living fossil".〔Flowering Plants of Africa 57:2-8(2001)〕 ''Welwitschia mirabilis'' is endemic to the Namib desert within Namibia and Angola.
==Scientific classification==
''Welwitschia'' is named after the Austrian botanist Friedrich Welwitsch, but the history of its naming was not straightforward. Welwitsch was the first to deliver an account of the species to Joseph Dalton Hooker of the Linnean Society of London in 1859.〔The Proceedings of the Linnean Society. Botany. Vol. V. London 1861 page 182-186. May be downloaded from: https://ia600607.us.archive.org/33/items/mobot31753002653522/〕 He originally supplied a brief technical description and proposed calling genus ''Tumboa'', after what he conceived to be the aboriginal name "tumbo". However, the artist Thomas Baines shortly afterwards supplied illustrations and some badly preserved specimens, plus the information that "tumbo" was not the specific name, but a rather general term, so Hooker asked Welwitsch for permission to name the genus ''Welwitschia'' instead. Welwitsch concurred and also supplied some well-preserved material from which Hooker was able to make substantial progress in deducing its botanical affinities.〔Hooker, Joseph Dalton. On Welwitschia, a new genus of Gnetaceae. Transactions of the Linnean Society v.24 (1864) pp 1-46. May be downloaded from http://archive.org/details/mobot31753002433701 〕 The taxonomic placement of ''Welwitschia'' subsequently changed intermittently with the development of new classification systems (see Flowering plants: History of classification). However, modern usage is close to the conclusions that Hooker drew.
Most botanists have treated ''Welwitschia'' as a distinct monotypic genus in a monotypic family or even order. Most recent systems place ''Welwitschia mirabilis'' in its own family Welwitschiaceae in the gymnosperm order Gnetales.〔Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008 http://www.mobot.org/MOBOT/research/APWeb/〕 The order Gnetales is most closely related to the order Pinales, which includes pines, spruces, larches and firs.〔Christenhusz, M.J.M., J.L. Reveal, A. Farjon, M.F. Gardner, R.R. Mill, and M.W. Chase (2011). A new classification and linear sequence of extant gymnosperms. ''Phytotaxa'' 19:55-70. http://www.mapress.com/phytotaxa/content/2011/f/pt00019p070.pdf〕 Genetic analyses indicate that the Gnetales arose from within the conifer group, and any morphological similarities between angiosperms and Gnetales are separately derived.〔Chaw S-M., C.L. Parkinson, Y. Cheng, T.M. Vincent and J. D. Palmer (2000) Seed plant phylogeny inferred from all three plant genomes: Monophyly of extant gymnosperms and origin of Gnetales from conifers ''Proceedings of the National Academy of Science of the United States of America 97:4086-4091〕 The ancestors of the extant gymnosperm orders - the Gnetales, Coniferales, Cycadales and Ginkgoales - arose during the Late Paleozoic, and became the dominant component of the Late Permian and Mesozoic flora.〔Wang, Z-Q. (2004) A new Permian Gnetalean cone fossil as evidence for supporting molecular phylogeny. ''Annals of Botany'' 94:281-288〕 Fossil evidence indicates that members of the Welwitschiaceae were present in South America during the Lower Cretaceous (Mesozoic era).〔Dilcher, D.L., M. E. Bernardes-de-Oliveira, D. Pons and T.A. Lott (2005) Welwitschiaceae from the Lower Cretaceous of northeastern Brazil. ''American Journal of Botany'' 92:1294-1310〕 Jacobson and Lester〔Jacobson, K.M. and E. Lester (2003). A first assessment of genetic variation in ''Welwitschia mirabilis'' Hook. ''Journal of Heredity'' 94:212-217〕 suggest that these early habitats of Welwitschiaceae were more mesic than the current desert conditions, and that the present fragmented and isolated population distribution could be attributed to aridification during the Tertiary and Quaternary, which restricted the plants to locales providing sufficient water for their needs.
The species has on occasion been given the name ''Welwitschia bainesii'' to honour its co-discoverer, Thomas Baines.〔http://www.plantzafrica.com/plantwxyz/welwitschia.htm〕 However, at present this is invalid and regarded as a synonym; currently there is just one species recognised, with one subspecies in addition to the autonymic subsp. ''mirabilis'': ''Welwitschia mirabilis'' subsp. ''namibiana'' Leuenb.
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