Dwarf trees in the fog
Of all the strange and wonderful trees around the world, perhapse the welwitschia is the species that looks like an extra-terrestial form of life. Half-buried in the sands of the lunar landscape of thr Namib Desert.
Tree Tombo NAMIBIA: Welwitschia mirabilis in the desert. It is surely one of the strangest plants in the world. Welwitschia has been called the "desert octopus" because of its huge heap of long leaves.
The Welwitschia mirabilis is unique to Namibia. It is in fact a coniferous dwarf tree that is related to the pine tree. It appears as though the Welwitschia has many intertwined leaves, but in reality there are only two leaves which continue to grow throughout its lifespan. As time passes, these two leaves are torn into thinner shreds.
With the family, genus and species all rolled into one, Welwitschia mirabilis truly is one of a kind. A rarity among rarities, it is a dwarf tree found only in the Namib Desert and on its fringes, northwards from the Kuiseb River. It grows mainly on gravel plains in the fog belt.
While welwitschias are classified with cycads and pines as cone-bearing plants, they are at the same time thought to represent a link to flowering plants. They live to a great age, as yet not known for certain, but possibly some 2 000 years. The largest trees are only 2m tall with a trunk diameter of 1,5m. Half of the trunk, or more, remains below ground.
A large colony occupies the Welwitschia Plain at the confluence of the Swakop and Khan rivercourses in the northern part of the Namib-Naukluft Park. One of the trees known as the Giant Welwitschia is estimated to be 1500 years old.
|A single pair of leaves is the sum total of the foliage that welwitschias produce in their lifetime. The leaves are actually the biggest part of the tree visible above ground. They grow from opposite sides of the trunk, straight out of a flattish, woody and dead-looking crown. Long and broad out of all proportion to the size of the trunk, they rather resemble floppy conveyor belts at first. In time they come to look like a lot of long narrow leaves lying in a tangle on the ground because the desert winds tear them to shreds.
Very tough and leathery, the leaves never really stop growing out of the crown for any length of time, not even in the driest years. Wear and tear at the ends keeps them more or less in check as they grow very slowly. They reach a length of about 3m. If they are browsed down to the trunk, or broken off, they immediately start to grow again.
Welwitschias absorb fog water through minute pores on their large leaves – 250 per square millimetre – as well as through lateral roots just below the soil. With taproots that are 3m long, they also depend on groundwater.
Male cones and female cones are borne on different trees. They first develop at about the age of 20, the female ones larger, the male ones more numerous. Like the leaves, they grow from the crown of the stem, but on stalks.
While pollen and seeds are produced in abundance, the odds against propagation are truly formidable. It is estimated that only one seed in a thousand reaches maturity. Thereafter at least 25mm of rain must fall, all at once or within two or three days, for germination to take place. Which is not exactly an everyday episode in the Namib.
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 that 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 (see below) has large cones while the male plant (see below) 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. 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 fertilization.
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.
Who is Afraid of the Tree Tumbo
Bushmen would call it N’tumbo (stump), the Afrikaans name is tweeblaarkamiedood (two-leaves-cannot-die), the English common name is tree tumbo, dr. Friedrich Welwitsch (in Slovene: Velbič), however, wrote about it on September 3rd 1859: ”I am convinced that what I have seen is the most beautiful and majestic the South Africa can offer.” Dr. Welwitsch kneeled in front of the plant on the hot sand and looked at it without actually touching it, for had he done so, the plant would, or at least he thought so, disappear like an apparition. His name is now immortalised not only in the name of this marvellous prehistoric plant species, its picture is also carved onto his tombstone. Let’s have a look at why the plant stirred up the explorer’s imagination and how the plant can be successfully grown in Slovenia.
Perhabs the oldest Welwitschia mirabilis in the National park of Namib-Naukluft in Namibia
photo: Vanja Kos . Carbon-dating of the largest Namibian trees indicates that they are more than 2000 years old.
Welwitschia (Welwitschia mirabilis)
- Yellowish-green leaves, to 6 feet long.
- Leaves die to brown and tear to shredded ribbons in the desert winds.
Shape and Trunk:
- Its sprawling ground-level mass of long dry leaves look as much like a dehydrated monster octopus as a tree.
- "Trunk" is an inverted cone, up to 4 feet in diameter, which descends 10 feet below the desert, but rises only 3 feet above ground-level.
- This trunk stores water for the tree. (Rain is absent from its Namib Desert for 3-out-of-4 years. A typical rainy year has about 1" of rain.)
- Trunk is hard (like hard wood); covered in a cork-like corrugated bark.
- Each tree is either male or female, and both have cones.
- A male tree has erect scarlet cones that rise 1 foot above the trunk.
- Pollen-producing flowers sprout from the flowers of the male cones.
- Insects carry the pollen to the female trees.
- After the plumper, erect female cones are pollinated, they produce small, winged, wind-borne seeds.
- Seeds can lie dormant for years.
- Grows wild and half-buried in northern gravel plains of Namib Desert.
- Regarded as a "living fossil" connected to the ancient flora of the Gondwanaland super-continent that existed millions of years ago.
- Has its own genus as it is so unlike other plants.
- Carbon-14 dating has found some Welwitschia mirabilis to be over 2,000 years old.
- Special pores on its leaves help it uses the dense sea fog and heavy dew that occur year-round.
- Its tangled torn leaves also help to condense air-borne moisture and guide it into the soil around its roots.
- Bitterness of leaves and bark deter predators.
- Emits a colorless resin that helps protect it from disease and insects.
- Plants may fuse together, either all male, all female, or a mixture. Groups of five have been found.
Young male flowering plant produces a red pollen which is Female plant - seed cones.Those are
transferred to the female flower. photo: Kenneth J. Sytsma Welwitschia beetles which feed off the sap
Female floweing plant is pollinated by a small insect ( Probergrothiussexpunctalis ) and the wind.
photo: Dennis W. Woodland.