The Living Fossil Welwitschia mirabilis
"The platypus of the plant kingdom"
Welwitschia mirabilis Hook F., locally known as Tumboa, or tree Tumbo, is a strange plant species that lives in the Namib Desert, from south-western Angola to west Namibia. In the scientific description of this strange plant, Joseph D. Hooker, at the time director of the Royal Botanich Gardens at Kew, wrote "it is out of the question the most wonderful plant ever brought to this country, and the very ugliest". However, wonder and astonishment are often described by the many who studied and still do. Often described as a halfway between a flowering plant and a conifer, in my opinion the best statement about this fascinating plant was made by Darwin who described it as "’the platypus of the plant kingdom".
Welwitschia plants are gymnosperms, belonging to division Gnetophyta, class Gnetopsida, in an order, Welwitschiales,and family, Welwitschiaceae, of its own to which they are the sole living species. It is considered a living fossil. Although it may not seem, just by looking at it, it is a creeping plant, consisting of a woody stem, most of it subterranean, and its two leaves that are shaped like a broad ribbon. The leaves, the most proeminant feature of these plants, continue to grow from the basal meristems throughout the whole life of the plant while their tips dye and dry out. As the years and ultimately the centuries pass, the wind and the scouring sand split the leaves longitudinally into ribbons, some ten inches or more wide. This also happens due to herbivores, insects and oryx antioples, feeding on the leaf base. Because it generally produces only two leaves, Welwitschia has been described by some authors as "a seedling arrested in development" or as "a plant without a head." The Welwitschia plant does not grow a huge taproot, but its stem can grow over 3 m deep while being up to 75 cm above ground. Over time, the leaves can reach great lengths, well over two meters and become ragged at the edges, or even fully throughout its length giving the impression that the plant has several leaves. It is a very slow growing plant, about 10 to 20 cm per year on natural conditions. Due to its unusual morphological features and the natural conditions where welwitschia grows it is difficult to assess the exact age of these plants. However, they are fully adapted to very dry and arid conditions. Using carbon-14 dating, scientists have estimated that some of the larger plants are as old as fifteen hundred or even two thousand years. Welwitschia mirabilis plant is dioecious, i.e. male and female cones grow on separate plants.
A Strange but Very Efficient Way of Survival
Although typical of the Namib desert, welwitschia is not exclusive to that region as it can also be found in subtropical grasslands to the east in Mopane woodlands, in Botswana. As an adaption to the arid climate in which Welwitschia lives, the leaves of Welwitschia can retain dew water in their surface grooves that run along their length. Off the shores of southwest Africa is the Benguela Current, which flows from south to north and is extremely cold. Warm onshore winds flowing over the cold water create a belt of fog that forms on the coast at night and often remains well into the morning. This condensed moisture is the main source of water for many lichens, animals and plants including Welwitschia mirabilis. As the leaves are twisted and deeply ragged in several directions they eventually drive the accumulated dew water to the ground around the plant. In this way, water then is absorbed by the root well below and stored in the stem. Often described as a prodigy of endurance, this species also shares a physiological characteristic in common with crassulacean plants (e.g. plants with fleshy and juicy leaves, such as cacti) in what collectively called the crassulacean acid metabolism, CAM. During the day, and to prevent water loss through transpiration, the leaves keep the stomata closed, thus minimizing carbon dioxide uptake during daytime and consequently limiting their photosynthetic capacity. However, unlike most plants, at night, when the temperature is down and the humidity is higher the stomata are opened. The carbon dioxide needed for photosynthesis, during the day, is then taken and stored it in the form of malic and isocitric acids in the vacuoles of its cells in the leaves. During the day, these acids are metabolized and the carbon dioxide is then used in photosynthesis. Therefore, basically photosynthesis is divided in two steps in these plants, at night they take the necessary carbon dioxide and during the day, like any other normal plant, welwitschia continues photosynthesis from the stored carbon dioxide keeping their stomata closed so that it does not lose water. Ultimately, like in any other plant, sucrose is produced as the main sugar and is transported throughout the whole plant body.
As a Symbol
This species was named after the Austrian explorer and botanist Friedrich Welwitsch, who discovered these plants in September 1859, near Cape Negro in Southern Angola, while working for the Portuguese government. The work of Friedrich Welwitsch, one of the foremost collectors of African plants, greatly contributed to the knowledge of welwitschia and many other plants from Angola. Welwitschia is a national symbol of Namibia and figures in the national coat of arms of Namibia and is also very popular as theme in postage stamps from Angola, Namibia and South Africa. Due to its unusual appearance Welwitschia plants are highly praised from collectors, especially big old specimens. This makes them threatened in its natural habitat, although, due to the long lasting civil war in Angola, from 1975 to 2002, and specifically due to the use of land mines, welwitschia plants are far better protected in Angola. A strange benefit from human wars one can say.Welwitschia plants are thus kept away from harmful human activity. However, in recent times, it became possible to grown them from seed in some botanical gardens and institutes as well as plant nurseries which contributed tremendously for its availability as an ornamental plant. This gives hope for its preservation in its natural habitat and also its widespread as a popular yet strange ornamental plant.
Southwest Africa: Home of Welwitschia mirabilis
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