Welwitschiaceae
| Welwitschiaceae Temporal range:Late Aptian-recent
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|---|---|
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| Welwitschia mirabilis | |
Scientific classification
| |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Gymnospermae |
| Division: | Gnetophyta |
| Class: | Gnetopsida |
| Order: | Welwitschiales |
| Family: | Welwitschiaceae Caruel |
| Type genus | |
| Welwitschia | |
Welwitschiaceaeis a family of plants of the orderGnetaleswith one living species,Welwitschia mirabilis,found in southwestern Africa. Three fossil genera have been recovered from theCrato Formation– late Aptian (Lower Cretaceous) strata located in theAraripe Basinin northeastern Brazil,[1]with one of these also being known from the early Late Cretaceous (Cenomanian-Turonian)Akrabou Formationof Morocco.[2]
Taxonomy[edit]
German naturalistFriedrich Markgrafcoined the name Welwitschiaceae in 1926, which appeared inDie Natürlichen Pflanzenfamilien.[citation needed]
Most recent systems place the Welwitschiaceae in thegymnospermorderGnetales.[3]This order is most closely related to the orderPinales,which includesAraucariaceae- Araucarians,Cupressaceae- Cypress Family,Pinaceae- Pine Family,Podocarpaceae- Podocarps, Sciadopityaceae - Koyamaki Family (the sole memberSciadopitys verticillata - Koyamaki),Taxaceae- Yew Family. Genetic analyses indicate that the Gnetales arose from within the conifer group, and any morphological similarities between angiosperms and Gnetales have evolved separately.[4]The ancestors of the extant gymnosperm orders—Gnetales, Coniferales, Cycadales and Ginkgoales—arose during the Late Paleozoic, and became the dominant component of theLate Permianand Mesozoic flora.[5]
Living species[edit]
The family contains a single genus and single extant species,Welwitschia mirabilis,which lives in theKaokoveldDesert of Angola and Namibia in southwestern Africa.[6]
Fossil species[edit]
Fossil evidence indicates that members of the Welwitschiaceae were present in South America during theEarly Cretaceous(Mesozoic era).[1]Priscowelwitschia austroamericana(initially namedWelwitschiellabut illegitimate due to the daisy genusWelwitschiella)[7]is a fossil taxon referring to some seedlings withcotyledonleaves. These have many features in common withWelwitschiaseedlings.[1]Welwitschiophyllum brasilienseis a taxon known from thick triangular to linear leaves that range from 8.9 to 70 cm long and 2.8–5 cm wide.[1]Welwitschiostrobus muriliis a fossil taxon known from some cones that resemble the livingWelwitschia,but are longer and thinner.[1]
Jacobson and Lester[8]suggest that these early habitats were moremesicthan the current desert conditions, and that the present fragmented and isolated population distribution could be attributed toaridificationduring thePaleogene,Neogene,andQuaternary,which restricted the plants to locales providing sufficient water for their needs.
References[edit]
- ^abcdeDilcher, David L.; Bernardes-De-Oliveira, Mary E.; Pons, Denise; Lott, Terry A. (2005)."Welwitschiaceae from the Lower Cretaceous of northeastern Brazil".American Journal of Botany.92(8): 1294–1310.doi:10.3732/ajb.92.8.1294.PMID21646150.
- ^Roberts, Emily A.; Martill, David M.; Loveridge, Robert F. (February 2020)."Phytogeographical implications of the probable occurrence of the gnetalean plant Welwitschiophyllum in the Late Cretaceous (Cenomanian) of Africa".Proceedings of the Geologists' Association.131(1): 1–7.doi:10.1016/j.pgeola.2019.10.002.
- ^Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 9, June 2008http://www.mobot.org/MOBOT/research/APWeb/
- ^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 conifersProceedings of the National Academy of Sciences of the United States of America 97:4086–4091
- ^Wang, Z-Q (2004)."A new Permian Gnetalean cone fossil as evidence for supporting molecular phylogeny".Annals of Botany.94(2): 281–288.doi:10.1093/aob/mch138.PMC4242163.PMID15229124.
- ^Bhatnagar, S. P.; Moitra, Alok (1996).Gymnosperms.p. 373.ISBN9788122407921.
- ^Dilcher, David L.; Bernardes-De-Oliveira, Mary E.; Pons, Denise; Lott, Terry A. (2005)."Welwitschiaceae from the Lower Cretaceous of northeastern Brazil".American Journal of Botany – Erratum.92(12): 1957.[dead link]
- ^Jacobson, K.M.; Lester, E. (2003). "A first assessment of genetic variation inWelwitschia mirabilisHook ".Journal of Heredity.94(3): 212–217.CiteSeerX10.1.1.495.1358.doi:10.1093/jhered/esg051.PMID12816961.