The welwitschia species has a longevity of several centuries (up to 1937 years according to some authors) and its largest known individual reaches 4 meters in diameter, according to a study published by our partner The Conversation.
It grows today exclusively in the Namib Desert, along a coastal strip of less than 168 km wide, from Namibia to Angola.
This “biography” of welwitschia was conducted by Germinal Rouhan, lecturer, systematic botanist and Serge Muller, professor (both researchers at the Institute of Systematics – evolution – biodiversity of the National Museum of Natural History).
Just like the ginkgo , the Chinese redwood and Wollemi pine , welwitschia belongs to the group of gymnosperms , the seeds of which are often protected in cones, as is the case with firs and spruces. Gymnosperms, unlike sophoras or catalpas for example, are therefore not flowering plants (called, they, angiosperms ).
The diversity of gymnosperms was maximum at Mesozoic (- 216 at -45 millions of years) before strongly regressing. Today only about a thousand species remain, especially widespread in boreal and mountainous regions.
Certain lineages of gymnosperms are no longer represented by one or some species, often considered as “relics” of these ancient groups. The welwitschia, which is found in the deserts of southern Africa, is one of these “relict species.”
How to recognize welwitschia?
Unique representative of its genus, of its family ( Welwitschiaceae ) and even of its order ( Welwitschiales ), welwitschia ( Welwitschia mirabilis Hook.f.) presents a short and thick trunk resulting from a taproot 2 to 3 m deep.
This trunk ends in a disc , on the edge of which develop only two opposite leaves, thick and leathery. They grow continuously throughout the life of the plant, and can reach dimensions of 2 to 4 meters, with a twisted, wavy shape, lying on the sandy or stony substrate.
The abrasive sand, the effect of which is increased tenfold by the winds, contributes to divide the sheets longitudinally into numerous strips, which then gives the illusion that these two unique laciniated sheets are much more numerous. The reproductive organs are cones, and since it is a dioecious species, the male and female cones are carried by different individuals.
The growth of welwitschias, like that of a tree, is visible in the concentric annual rings of the trunk, and the age of individuals can therefore be roughly estimated by counting these rings. The species has a longevity of several centuries, even up to 1863 years according to some authors. The largest known individual, “The Big Welwitschia”, reaches 1.4m in height and 4m in diameter with its foliage. The Namib Desert (Southern Africa) is the only place in the world where Welwitschia mirabilis grows naturally.
In his novel
Le Tour du monde d’un gamin de Paris , published at the end of the 19th century, Louis-Henri Boussenard makes it the following description:
” A veritable forest grew as far as the eye could see. We say forest, because there is no other word to denote in general an agglomeration of trees and in particular that of welwitschias . These trees, stocky, or rather flattened, had taken all their development in width. The trunk seemed like an enormous log hard as ironwood from which escaped two single leaves, woody, thick, monstrous, two meters long and seventy-five centimeters wide. The impression produced by the sight of these vegetable legless was stupefied, almost disgusted. . It’s too much. Never, since the world became world, has we seen anything like it. “
” It is a plant that I do not hesitate to consider from a botanical point of view as the most wonderful that has been discovered in the present century. »
After extensive discussions with other biologists, in particular Charles Darwin (who compares it to a plant platypus!), Hooker describes and illustrates it in 1382 at the request of Welwitsch.
Hooker dedicates the new genre to his Austrian discoverer, after having convinced the latter to give up the name that ‘he proposed, Tumboa – a vernacular name that local people applied to the plant in question (which they therefore already knew), but also to other plant species.
At ease in the deserts of southern Africa
Welwitschias today grow exclusively in the Namib Desert, along a coastal strip of less than 190 km wide, from the Na mibie to Angola.
Although no surface water is permanent there, the plant seems adapted to this environment: if aridity reigns here, there is also the humid freshness coming from the coast and its mists. Condensing as dew overnight, the water in the mist is picked up by the leaves, as the broad, conical root sinks deep enough into the ground to reach underground moisture at the same time as it firmly anchors the plant in the sand.
Even in deserts without any annual precipitation, welwitschias do much more than ‘subsist there, since they are also capable of reproducing there. Ripe seeds remain viable for years until a period of rain of several days arrives: it is such an exceptional event that the plants of some populations are all the same age, being the result of germinations that have taken place. during a rare and unique rainy year.
Despite very large withdrawals and now regulated , l he species is still quite abundant although it is necessarily restricted to the deserts of Namibia and Angola. However, recent studies have established its vulnerability to climate change, and lead to the report of certain populations in danger of extinction.
The question of the conservation of the species is relevant over the entire range, since it is in fact represented by several populations corresponding to two subspecies, mirabilis in Angola and namibiana in the southern part of the range. The subspecies namibiana was first detected in culture at botanical garden Berlin-Dahlem in 2001 and reflects differences in phenology and morphology at the level of the male cones. Researchers have estimated that these differences would justify recognizing two species in their own right.
Where to see welwitschias?
From due to its ecological requirements, of course, the species could not be acclimatized outdoors in parks or botanical gardens in our temperate climates. But it is cultivated and can be admired in the greenhouses of desert plants, present in many French botanical gardens, in Paris, Nantes or even Nancy, as well as in Brussels, Berlin, London, Basel … By going a little further , in the botanical garden of Kirstenbosch (South Africa), you can even visit a greenhouse dedicated to this flagship species, the Welwitschia House .
Unclassifiable since his discovery, Welwitschia perplexed scientists, due to the difficulties in determining its nature and its relationship to other plants.
The only current species of its genus, of its family and even of its order, it is placed in the class of Gnetopsida with two other current plant genera, Ephe dra and Gnetum . But the kinship relationship between Gnetopsida and other plants remains uncertain. Indeed, the Gnetopsida present morphological affinities with angiosperms (flowering plants) as well as with current gymnosperms (conifers , ginkgos, cycads), which is why they were first considered as a transitional group in the evolution of seed plants.
The work of Shu- Miaw Chaw, recently supported by those of Jin-Hua Ran in phylotranscriptomics, revolutionized this idea by showing that genetic data could favor a completely different evolutionary hypothesis, which confirmed Welwitschia and the others Gnetopsida as gymnosperms, but in the position of closest relatives of the family of Pinaceae (firs, pines…) among conifers!
This would imply that the morphological characters shared between angiosperms and Gnetopsida would have appeared twice independently in c bear of plant evolution. This is a hypothesis that remains controversial because the shared characters relate to complex structures, such as reproductive organs which are similar to flowers and involve double fertilization. Thus, the placement of Welwitschia and others Gnetopsida remains debated in the phylogenetic reconstruction of the tree of life. More than 150 years after its “discovery” , Welwitschia still remains a mystery…
This analysis was written by Germinal Rouhan, lecturer, systematic botanist and Serge Muller, professor (both researchers at the Institute of Systematics – Evolution – Biodiversity of the National Museum of Natural History). The original article was published on the website of The Conversation .
Welwitschia mirabilis from Namibia © Thomas Schoch / Wikimedia, CC BY-NC-SA 
Female cones © Hans Hillewaert, CC BY-NC-ND (via The Conversation) 
Welwitschia House .
