Welwitschia
| Welwitschia | |
|---|---|
| |
| Scientific classification | |
| Kingdom: | |
| Division: | |
| Class: | |
| Order: | Welwitschiales
|
| Family: | Welwitschiaceae
|
| Genus: | Welwitschia
|
| Species: | W. mirabilis
|
| Binomial name | |
| Welwitschia mirabilis | |
Welwitschia is a monotypic genus of gymnosperm plant, composed solely of the very distinct Welwitschia mirabilis. It is the only genus of the family Welwitschiaceae, in the order Welwitschiales, in the division Gnetophyta. The plant is considered a living fossil.[1]
The geographic distribution of Welwitschia mirabilis is limited to south-west Africa, specifically, to the Namib desert within the two countries, Namibia and Angola.
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Biology
Welwitschia grows from a short, thick trunk, with only two leaves that continuously grow from their base, and a long, thick taproot. After germination, the cotyledons grow to 25–35 mm in length, and are followed shortly afterwards by the appearance of two permanent leaves. These leaves are produced opposite of the cotyledons, and continue to grow throughout the entire life of the plant. They eventually grow to a length of 2–4 m and usually become split into several strap-shaped sections, thus sometimes disguising the origin from only two leaves. After these appear, two cotyledonary buds appear; in these, the growing tip dies, causing elongation of the buds. Growth continues sideways, which forms the obconical growth of the stem. The species is dioecious, with separate male and female plants. Fertilization, that is, the transfer of the pollen from the male to the female flowers, is apparently carried out by insects that are attracted by nectar produced on both male and female flowers.[2]
The age of the plants is difficult to assess, but it is believed that they are very long-lived, possibly living 1000 years or more. Some individuals may be more than 2000 years old.
The plant is thought to absorb water through peculiar structures on its leaves, harvesting moisture originating from dew that forms during the night. As a further adaptation to the arid conditions and hot daytime temperatures in its environment, and as the only gymnosperm species known to do so, W. mirabilis uses the crassulacean acid metabolism (CAM) pathway for carbon fixation in photosynthesis.[3] Named after the Slovenian botanist Dr. Friedrich Welwitsch who discovered it in 1860, it is generally considered to be one of the oddest plants in existence. Although considered endangered due to its very slow growth and despite the fact that older plants are often sought by collectors, a fair number of plants exist in the wild. The plants living in Angola are generally considered to be better protected than the plants in Namibia, owing to the relatively high concentration of landmines in Angola, which keep collectors away [citation needed].
The species grows readily from seed, which may be purchased from specialty seed dealers. The seed must be kept moist for the first couple of weeks and exposed to as much heat and light as possible during this time. Seeds collected from the wild are often heavily contaminated with spores of Aspergillus niger, which causes them to rot shortly after they germinate. Seeds from the Kirstenbosch National Botanical Garden in Cape Town, South Africa, or other cultivated sources are much cleaner and less likely to rot. [citation needed]
Scientific classification according to different sources
| After Systema Naturae 2000 | After University of Connecticut 2006 [2] | After ITIS (Integrated Taxonomic Information System) 2005 [3] | After Encyclopedia Britannica Online 2007 [4] | |
| Domain | Eukaryota | - | - | - |
| Kingdom | Plantae Haeckel, 1866 |
Plantae | Plantae | - |
| Subkingdom | Viridaeplantae Cavalier-Smith, 1981 |
- | Tracheobionta | - |
| Division | Tracheophyta Sinnott, 1935 ex Cavalier-Smith, 1998 |
Gnetophyta | Gnetophyta | Gnetophyta |
| Subdivision | Spermatophytina (auct.) Cavalier-Smith, 1998 | - | - | - |
| Infradivision | Gymnospermae auct. | - | - | - |
| Class | Gnetopsida | Welwitschiopsida | Gnetopsida | - |
| Order | Gnetales T.M. Fries, 1891 | Welwitschiales | Welwitschiales | Welwitschiales |
| Family | Welwitschiaceae Markgraf in Engler & Prantl, 1926 | Welwitschiaceae | Welwitschiaceae Markgr. | Welwitschiaceae |
| Genus | Welwitschia J.D. Hooker, 1862 | Welwitschia | Welwitschia J. D. Hooker, 1863 | Welwitschia |
| Species | Welwitschia mirabilis J.D. Hooker | Welwitschia mirabilis Hook. f. | Welwitschia mirabilis Hook. f. | Welwitschia mirabilis |
| In green | In green | In green | Identical names with different authors |
| In red | - | - | Different names with different authors |
Heraldry
The plant figures as a charge in the national coat of arms of Namibia, as well as that of Westelike Rugby Subunie.
See also
References
- ^ A. Lewington & E. Parker (1999). Ancient Trees: Trees that Live for a Thousand Years. Collins & Brown Ltd. ISBN 1-85585-704-9.
- ^ Wetschnig W, Depisch B (1999). "Pollination biology of Welwitschia mirabilis HOOK. f. (Welwitschiaceae, Gnetopsida)". Phyton-Annales Rei Botanicae. 39: 167.
- ^ von Willert DJ, Armbruster N, Drees T, Zaborowski M (2005). "Welwitschia mirabilis: CAM or not CAM - what is the answer?". Functional Plant Biology. 32: 389. doi:10.1071/FP01241.
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External links
