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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