Welwitschia Mirabilis Plants
The WELWITSCHIA TRAIL lies east of Swakopmund and offers a close look at a botanical curiosity endemic to the Namib Desert and is one of the most intriguing and bizarre plants. It is a self-guided trail which takes you through the ''Moon Landscape'' to the Welwitschia Mirabilis.
(A permit is required.)
The first Welwitschia plant was discovered by Austrian botanist Friedrich Welwitsch in 1860 in the Namib Desert in the southern part of Angola. The plant was named after Friedrich in recognition of his successful botanical research and because he found and collected it first.
This Welwitschia is a plant of remarkably bizarre habits and survives in very harsh localities where the annual rainfall is often less that 25 mm and where the coastal fog is equivalent to about further 50 mm. The oldest living Welwitschia specimens are estimated at 1500 to 2000 years is capable of surviving severe conditions of stress. Most of the observations are done on the Welwitschia Fläche, a desert plain, about 50 km east of Swakopmund and east of the confluence of the Khan and Swakop rivers.
The Welwitschia is considered to be a gymnosperm, although the relationship with other species in this class is not clear. The position of the Welwitschia in the hierarchy of the plant remains tenuous.
The Welwitschia is endemic to the Namib Desert, i.e. found only in the area. The Namib Desert is one of the world oldest deserts with extreme arid conditions stretches in the western part of Namibia along the coast up to the south-western part of Angola. The Welwitschia is restricted to a narrow path of this desert.
The plant resembles a woody carrot. The stem is exceedingly fibrous and has a prominent, thick, corrugated periderm. Unequal growth causes the stems of these plants to become weirdly distorted and there are only two strap-shaped leaves, growing from a terminal groove in the photosynthetic tissue of the stem.
One of the most magnificent specimens is found in the Welwitschia Fläche. One of the large plants measure 1.5 m from the soil surface to the highest part of the stem. The Pforte Welwitschia is 1.2 m tall and the circumference at the base of it’s' leaf is 8.7 m. The roots of Welwitschia can grow up to 30 meters deep, sponge and lateral roots are also a part of the root system.
The leaves are the longest-lived in the plant kingdom, they are evergreen, a single pair and generally broad and flat. The broadest unbroken leaf is found in the Fläche measures 179 sm. This particular leaf was 6 meters long of which 3.15 meters were living tissue. The surface that this leaf covers helps the plant to survive at a temperature on the soil as high as 65 'C. It keeps the soil under the plant cool and moist. The leaves grow annually an average 13.8 sm. Therefore the plant can produce up to 150 m of leaf tissue over a growth period of 1000 years. The leaves are on average 1.4 mm thick. The leaves that lay on the sand surface also prevent wind erosion. Even under gale force conditions the broad leaves remain rigid and immobile. Absorption of water through the stomata must be regarded as very interesting, this characteristics of the leaves has ensured the species survival. The stomata remains open until the fog has lifted and although much of the water that has condensed on the leaves runs off the direct intake of a proportion of this water takes place.
Unlike other plants the stomata is open under foggy conditions and closes when it is hotter. This ensures that no water is evaporated during the heat of the day.
The female plant has large cones while the male plant has flowers. The male reproductive structure has six stamens each with an anther and a pistil. A female plant of average size may bear from 60 to 100 or even more cones. The Welwitschia female plant can produce a lot of seeds: up to 10 000 or even more. Unlike other known plants fertilisation occur in the pollen tube rather than in the embryo sac. It is known that wind plays a major role in the fertilisation, but much has to be learned about a little insect (Probergrothiussexpunctalis) which also helps with the fertilisation.
Seed and seedling:
The seed units consist of a seed and a paper husk of winged segments. It is suggested that very strong wind would be required to successfully distribute the seeds. Most of the seeds that are shed have a very little chance of germinating. Assuming that 50% of the seeds are fertile and 80% of that seeds are infected with a fungus (Aspergillus niger). However, it is doubted that one-hundredth of 1% of all seeds produced germinate and develop into a mature plant. Seeds that are moisturized excessively do not germinate but develop an extremely unpleasant odour.
Most plants absorb water from the soil through their roots. This water is then transported to the stem and the roots and the water is then lost through the stomata evaporation. The Welwitschia plant works the other way around. It is able to absorb water from fog through millions of stomata on the surface of its large leaves. From there the water moves to the rest of the plant.