ie.obsculta-music.at
Information

Welwitschia

Welwitschia


We are searching data for your request:

Forums and discussions:
Manuals and reference books:
Data from registers:
Wait the end of the search in all databases.
Upon completion, a link will appear to access the found materials.


Welwitschia is a monotypic gymnosperm genus, comprising solely the very distinct Welwitschia mirabilis, endemic to the Namib desert within Namibia and Angola.

Click on the photo or the name of the succulent plant for which you wish to see further information.

Back to Browse Succulents by Genus.
You can also browse succulents by Scientific Name, Common Name, Family, USDA Hardiness Zone, Origin, or cacti by Genus.


Contents

Welwitschia is named after the Austrian botanist and doctor Friedrich Welwitsch, who was the first European to describe the plant, in 1859 in present-day Angola. Welwitsch was so overwhelmed by the plant that he, "could do nothing but kneel down [. ] and gaze at it, half in fear lest a touch should prove it a figment of the imagination." [4] [5] Joseph Dalton Hooker of the Linnean Society of London, using Welwitsch's description and collected material along with material from the artist Thomas Baines who had independently recorded the plant in Namibia, described the species. [6] [7]

Welwitsch proposed calling the genus Tumboa after what he believed to be the local name, tumbo. Hooker asked Welwitsch for permission to name the genus Welwitschia instead. Welwitsch concurred and supplied some well-preserved material from which Hooker was able to make substantial progress in determining its botanical affinities. [8] The taxonomy of Welwitschia subsequently changed intermittently with the development of new classification systems (see Flowering plants: History of classification), however, its current taxonomic status is essentially the same as Hooker's placement.

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, although other extinct species have been placed in this family. [9]

After germination, the seedling produces two cotyledons which grow to 25–35 mm (0.98–1.38 in) in length, and have reticulate venation. [10] Subsequently, two foliage leaves are produced at the edge of a woody bilobed crown. The permanent leaves are opposite (at right angles to the cotyledons), amphistomatic (producing stomata on both sides of the leaf), parallel-veined and ribbon-shaped. Shortly after the appearance of the foliage leaves, the apical meristem dies and meristematic activity is transferred to the periphery of the crown. [11]

The two foliage leaves grow continuously from a basal meristem reaching lengths up to 4 m (13 ft). The tips of the leaves split and fray into several well-separated strap-shaped sections by the distortions of the woody portions surrounding the apical slit, and also by wind and adventitious external injuries. [11] [12] The largest specimens may be no more than 1.5 m (4.9 ft) tall above ground, but the circumference of the leaves in contact with the sand may exceed 8 m (26 ft). [13]

Welwitschia has an elongated shallow root system consisting of "a tapering taproot with one or more non-tapering extensions, some pronounced lateral roots, and a network of delicate spongy roots" [13] and a woody fibrous unbranched main stem. [11] The roots extend to a depth roughly equal to the span of the living leaves from tip to tip. [11] The main stem consists of an unbranched woody crown roughly shaped like an inverted cone. [14] The only branching in the shoot system occurs in the reproductive branches, which bear strobili.

The species is dioecious, with separate male and female plants. Fertilization is carried out by insects including flies and true bugs. The most common of the true bugs attending Welwitschia is a member of the family Pyrrhocoridae, Probergrothius angolensis, but a hypothesized role in pollination has so far not been demonstrated. Infrequently, wasps and bees also play a role as pollinators of Welwitschia. At least some of the pollinators are attracted by "nectar" produced on both male and female strobili. [15]

Welwitschia has been classified as a CAM plant (crassulacean acid metabolism) after reconciliation of some initially contradictory and confusing data. [16] [17] There are however some very puzzling aspects to the matter for example, the employment of the CAM metabolism is very slight, which was part of the reason that it took so long to establish its presence at all it is not understood why this should be.

The age of individual plants is difficult to assess, but many plants may be over 1000 years old. Some individuals may be more than 2000 years old. [11] Because Welwitschia only produces a single pair of foliage leaves, the plant was thought by some to be neotenic, consisting essentially of a "giant seedling." However, research showed that its anatomy is not consistent with the giant seedling idea. Instead, the plant is more accurately thought of as achieving its unusual morphology as a result of having "lost its head" (apical meristem) at an early stage. [18]

Welwitschia mirabilis is endemic to the Kaokoveld Desert, [19] which lies within the Namib Desert. [20] The population is distributed southwards from the Bentiaba River in southern Angola, to the Kuiseb River in Namibia, [21] and up to 100 km (62 mi) inland of the coast. [11] The area is extremely arid: the coast is recorded as having almost zero rainfall, while less than 100 mm (3.9 in) of rain falls annually below the escarpment in the wet season from February to April. [19] Populations tend to occur in ephemeral water courses, indicating a dependence on ground water in addition to precipitation from fog. [22]

Welwitschia mirabilis grows readily from seed, which may be bought from specialty seed dealers. The seeds have been shown to display orthodox seed behavior, which in general means that they may be stored for long periods at suitably low humidity and temperature. Welwitschia seeds naturally develop suitably low water concentrations as they ripen. [23] Removal of the outer seed coverings enhances germination performance, which suggests that the seeds may display non-deep physiological dormancy. [23] On planting the seed it is necessary to keep it moist, but not immersed in water, for the first two weeks of cultivation it has been suggested that soaking the seeds in water before planting interferes with germination. [23]

Seeds collected from the wild often are heavily contaminated with spores of the fungus Aspergillus niger var. phoenicis, [24] which causes them to rot shortly after they germinate. The fungal inoculum infects the growing cones of W. mirabilis early during their development, and a sharp increase in infection occurs when the pollination drops appear through those drops the fungal spores may gain access to the interior of the developing seed. [25] Seeds in the wild may therefore be obliterated through fungal action even before they are fully developed. Seeds from botanical gardens or other cultivated sources are much cleaner and less likely to rot. The fungicide tebuconazole may be useful in controlling limited A. niger seed infection. [25]

The population of Welwitschia mirabilis in the wild is reasonably satisfactory at present. Plants in Angola are better protected than those in Namibia, because of the relatively high concentration of land mines in Angola, which keep collectors away. [5]

Although Welwitschia mirabilis is not at present immediately threatened, there being abundant populations over a large area, its status is far from secure its recruitment and growth rates are low, and its range, though wide, covers only a single compact, ecologically limited and vulnerable area. The remarkable longevity of Welwitschia favours its survival of temporary periods adverse to reproduction, but it offers no protection against circumstances of direct threat, such as overgrazing and disease. Fungal infection of female cones severely reduces seed viability, reducing already inherently low recruitment. Other threats include injury from off-road vehicles, collection of wild plants and overgrazing by zebras, rhinos, and domestic animals. [26]

The plant figures as a charge in the national coat of arms of Namibia.


Welwitschia mirabilis

Published by Daniel Mosquin on August 28, 2014

The second-last in the plants and biomes of South Africa series is featured today. Taisha writes:

Today, we take a slight detour from South Africa, as this species is not present in the country. Welwitschia is found only in the Namib Desert of Namibia. However, the Namib Desert slightly extends into South Africa where it forms the country’s sole area of desert biome. The Namib Desert is one of the smallest and oldest deserts in the world. I chose Welwitschia as it has not been featured on Botany Photo of the Day before and it was not easy to find a plant species in the Botany Photo of the Day Flickr Pool to represent this biome. Still, this species is an interesting representative for the desert. Daniel contributed these photographs of Welwitschia mirabilis from Huntington Botanical Garden.

As implied above, the desert biome occurs in only a small part of northwestern South Africa, primarily the Springbokvlakte area of the Richtersveld. The altitude is between 600 and 1600 m, which results in a slightly cooler climate than other true deserts (though it remains more climatically extreme than the succulent Karoo and the Nama-Karoo biomes). Temperatures can be hot, up to 45°C. Similarly extreme, temperatures can drop over 20°C from day to night. Winter temperatures can be as low as -12°C. Fog from the nearby Atlantic Ocean accounts for much of the precipitation, although there is some variable summer rainfall (

10-80mm annually). True deserts are largely sandy with low organic material in their soils.

The vegetation within the desert biome is typically annual grasses and other plants. After a season with rarely abundant rains, short annual grasses may grow, whereas in most years the annual plants persist as seeds. Some perennials may survive, particularly in areas associated with local concentrations of water.

Welwitschia mirabilis is a monotypic species of the Welwitschiaceae under the plant Division Gnetophyta–a small group of seed plants that have intermediate characteristics between gymnosperms and angiosperms. The oldest specimens of Welwitschia in the Namib Desert are thought to be more than 1500 years old, and recent fossil evidence suggest that Welwitschia was present during the Cretaceous (

112 million years ago). Some photos of the plant in habitat are available via Wikimedia Commons: the biggest known plant and a couple plants in the landscape.

This dioecious (male and female individual plants male and female cones are shown above) evergreen species has a woody unbranched stem that is shaped like an inverted cone. The stem is surrounded by a bi-lobed crown of green photosynthetic tissue. There are only two opposite, persistent, ribbon-like leaves that grow continuously from a basal meristem and die off at their tips over time. Unique among all extant plant species, after the first two leaves form, the terminal bud dies and the apical meristematic activity is transferred to the periphery and base of the leaves. In other words, it has ever-growing persistent leaves, with the leaf ends being the oldest part of the leaf.


Onyanga (Desert Onion)

Welwitschia mirabilis grows in isolated communities in the Namib Desert in central Namibia to southern Angola. The plants are seldom found far from the coast, and the distribution coincides with the fog belt. Welwitschia is still somewhat common in its habitat and shows variability, a sign that the species is not near extinction. Although the plant is not endangered, it is protected by law. Rainfall in Welwitschia's natural habitat is erratic and extremely low often, there are years with no rainfall at all. Welwitschia is ecologically highly specialized and is adapted to grow under these arid conditions in areas that receive regular fog. Welwitschia leaves are formed so that it waters its own roots by collecting condensation, and the leaf surfaces have numerous stomata (microscopicpores) through which condensation is absorbed. Welwitschia also has a long taproot, allowing it to reach water deep underground. Antelope and rhinoceros chew Welwitschia leaves for hydration during times of drought. The cone of the female plant was used as food for people in earlier times it was eaten raw or baked in hot ashes. The plant's common name is onyanga, which means "onion of the desert."

United States Botanic Garden Conservatory
100 Maryland Avenue, SW, Washington, DC 20001
(202) 225-8333


Watch the video: DRIVING THROUGH OMARURU TOWN IN MARCH 2021 CENTRAL NAMIBIA SOUTHERN AFRICA