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Welwitschia Mirabilis
The first
Welwitschia plant was discovered by
Austrian botanist Friedrich Welwitsch (1806-1872)* 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 than
25 mm and where the coastal fog is equivalent to about further 50 mm.
The Welwitschia's oldest living 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
specimen 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
its leafs 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.
Leaf characteristics. The leafs 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 leafs 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. Absorbtion 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.
Reproductive anomalies. The female plant has large cones while the male
plant has flowers. The male reproductive structure has six stamens each
with a 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. I 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 consists 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.
Water absorption. 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 it's large leaves. From there the
water moves to the rest of the plant. Conclusion. Serious doubts have
been expressed as to whether this wonderful plant, Welwitschia, is not
perhaps facing an extinction. Considered against this plant longevity
and remarked adaptation to it's environment, there should be no reason
for concern. It is proper thought that this plant be awarded the National
protection it deserves and in this respect it is extremely gratifying
to know that the Welwitschia Fläche where the oldest and largest
plant occur has now been incorporated into the Namib Naukluft park.
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