The Phyto-Philes - Welwitschia
Created | Updated Jun 23, 2013
Welwitschia
Willem says: 'The Phyto-Philes are for plant lovers of every size and shape, colour and flavour. As with my Colours of Wildlife column, I'll be featuring one species per article, illustrated with sketches, paintings, and/or photos. Over time I hope to be showcasing the amazing diversity of weird and wonderful plants that occur in South Africa, while also from time to time looking at the flora of other countries. While featuring many spectacular species, I'll not be neglecting the smaller, more humble kinds that are nevertheless fascinating in their own right.'
Here is another very weird plant for you. This is the Welwitschia, Welwitschia mirabilis. This is a species I have not yet seen in habitat or grown although I did get some seeds and tried, but without success. It occurs in Namibia – a country I have been to – but I haven't been to the regions where these ones grow. I was in the central south whereas Welwitschias grow in the north and closer to the coast, and also in neighbouring regions in Angola. It was named for Austrian botanist Dr. Friedrich Welwitsch, who discovered it in 1859, and its species name mirabilis means 'wonderful' or 'amazing'. Dr. Welwitsch's tombstone in London bears an image of a Welwitschia.
A Headless Tree
This, like the spiny baboon's poison featured last time, is one of those 'just what in the world am I looking at' plants. When you stumble upon one, you might think someone has dumped some garden refuse in the desert. It looks just like a big pile of tattered leaves and plant fibres. But if you go closer you'll see that it is in fact a single, living, growing plant. It is indeed a tree of a kind – a tree that lost its head! All other trees have growing tips from which new leaves and branches can form. The Welwitschia, however, 'loses its head' shortly after germinating: its tip dies and its original two leaves formed after the two seed leaves are the only ones it ever has for the rest of its life. But these two leaves keep growing for its entire life! They just grow longer and longer and longer. The harsh desert winds whipping the sand about shred the tips of these leaves into tatters, but they keep on growing from their base, also broadening around the circumference of the stem tip. Meanwhile the 'trunk' of the plant slowly gets thicker and thicker, and while no further lengthening happens at the tip, the thickening proceeds outwards from the dead tip and can eventually form a large, very thick mound protruding up to a meter and a half from the soil surface. My first sketch shows a view from the top of a medium-sized specimen showing how the stem grows outward from the 'dead head' of the growth tip at the center, with the two leaves growing around its margin and splitting lengthwise. Below the sand surface there can be another meter or so of 'trunk', and below that a taproot with many spongy rootlets that sustain the plant by seeking out groundwater. The leaves can be many meters long including their shredded tips. But since its growth is very slow, very large individuals could be over a thousand years old. Their leaves are therefore also the longest-lasting leaves in the plant kingdom.
A Most Unusual Conifer
Apart from its weird appearance the Welwitschia is amazing for its relationships. It bears cones and is therefore related to conifers like pines, cedars, yews, spruces and so. But it looks utterly unlike any of those conifers. It is also distantly related to cycads, which also bear cones and which also look very different from it. Its closest relatives are trees, shrubs and vines in the genus Gnetum, and the shrubby Ephedra bushes from which the stimulating drug Ephedrine is extracted. These, too, look nothing like the Welwitschia, but the proof of their relationship is in the structure of their cones, and is confirmed with genetic investigations as well as finds of more fossil species. Ephedra also grows in temperate to cold, arid or semi-arid regions, and have tiny, scale-like leaves, but Gnetum grows in tropical rainforests, and have well-developed, broad leaves. Together these three groups indicate that the conifers in the past must have been very much more diverse than they are today. It is difficult to even try to imagine the 'missing links' that must have existed between all these forms.
In the Welwitschia, male and female plants are separate. Male cones are small, narrow, and borne more numerously – my painting is of a large male. Female cones are rounder and borne in smaller numbers. Here are sketches showing both, first the male then the female. This species is pollinated by insects: flies and bugs, mainly, but also sometimes wasps and bees. The male and female cones both produce small amounts of nectar attracting these insects. In this the Welwitschia more resembles flowering plants than conifers, and was once thought to be a link between them and the flowering plants, but now it is thought to have developed its interesting flower-like cones independently.
After fertilization the seeds mature in the female cones, which eventually disintegrate to release them. They are flat with papery 'wings' and are distributed by the wind. Many are eaten by animals but if not they can remain viable for a number of years. They germinate only when moistened sufficiently, and so Welwitschia seedlings tend to establish themselves in large numbers during rare years of outstanding rainfall. So you may find groups of similarly-aged Welwitschias with their ages corresponding to the years of exceptional rains in these deserts.
Sustaining Sea-fogs
Once a seed has germinated the seedling seems to need a miracle: it is young and tender and can thank its very existence to freak rainfall that is unlikely to reoccur for many years. How does it survive? The answer: fog! These plants grow close to the coast of northern Namibia. Although rains almost never happen, fogs are very frequent. The cold Benguela ocean current flows from Antarctic waters northwards along the coast of Namibia. When it meets hot air blowing from the Namib desert it cools it down sufficiently for moisture in the air to condense into small droplets of fog. This is also assisted by the fact that deserts cool down much more at night than well-vegetated countryside does. So the fogs form during the night and dissipate again in the morning. But the Welwitschia, like many other plants of these deserts, is adapted to absorb the droplets of fog through its leaves. These have pores called stomata. Other plants also have pores in their leaves, but only for exchanging air, while the Welwitschia can use them to 'suck in' this moisture! When the fog lifts and the sun shines the stoma closes to prevent the collected moisture from evaporating. Also, fog not collected by the leaves flow along the grooves in their upper surfaces to the leaf tips where they collect and penetrate into the ground where the spongy roots can absorb them.
This fog does contribute to the Welwitschia's water needs but is not enough in itself. So the plants often grow where they can get at some groundwater too, such as around watercourses. While the rivers may only show surface water in years of high rainfall, they may contain subterranean water year-round. Also Welwitschias sometimes grow in rocky regions where water can collect in cracks and crevices between the rocks. The leaves and tattered leaf-remnants lying around the trunk shade the soil surface, which exposed may reach temperatures of 65 degrees Celsius, cooling the root system and also preventing the winds from exposing it by blowing the soil away. The Welwitschia is typically the largest and most conspicuous plant in its habitat. In the regions of higher rainfall the Welwitschias become smaller. This is probably because here they compete with other plants and no longer have the advantages that enable them to survive so well in the desert, where almost nothing else can. Almost no animals eat them, but antelope and rhinos will chew the leaves and spit them out again during droughts, to obtain a bit of moisture. The Welwitschia's unique survival mechanisms combined with this unique ecosystem are why the species, the last of its kind, still exists today.
Growing Welwitschia
Like I said, I did try but had no success germinating Welwitschia seeds. They are very susceptible to fungal attacks. They should therefore be treated with a fungicide (which I didn't do) and actually once the seedlings are established, typically when eight months or more in age, the plant appears to do well and be grown fairly problem-free. They are currently being grown at the Kirstenbosch Botanic Gardens, and several succulent enthusiasts have reported success with them. They are not true succulents, though, and should not be kept in too dry conditions. Detailed advice on growing them can be found here.
