Welwitchia Mirabilis
Plants
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.
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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.
Leaf characteristics:
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.
Reproductive anomalies:
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.
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 its large leaves. From there the water moves
to the rest of the plant. |
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