The Namib desert is considered the oldest in the world. Characterized not only by its high aridity, but also by its extreme temperatures, very few plants can survive in such a hostile environment. However, there is one species in the region that is practically iconic, a national symbol of Namibia and one of the most fascinating plants known: Welwitschia mirabilis .
Where and how do you live?
Despite living in the middle of the desert, where the average rainfall is around 25 millimeters a year, with cold nights in winter and summers with extreme sunshine, this plant is relatively large. Morphologically, it has a wide, stocky stem, no more than a meter and a half high, but its leaves can spread horizontally to cover more than eight meters in diameter.
It is a dioecious species, that is, the male and female flowers appear on different individuals. It is pollinated by insects, mainly flies and bugs. The plant has a peculiar root system. It has a central conical root that burrows into the substrate, generally made up of gypsum, and from which a horizontal network of spongy roots extends. Although rainfall is very rare, coastal fogs can carry enough moisture and form dew to supply Welwitschia with water.
To do this, the leaves have an extremely hydrophilic surface, which retains environmental humidity and makes it available to the plant. The system is so effective that it has been proposed as a model for the manufacture of nanomaterials capable of effectively condensing dew and capturing fog.
A recent study further suggests that the roots may also obtain water from the crystallization of the gypsum rocks in which they settle.
The extreme longevity of its leaves
Unlike other plants, in Welwitschia the apical meristem of the stem – the part where the stem of the plant grows – dies prematurely and growth activity is focused on its leaves. This phenomenon gives rise to what is probably the most striking feature of this species.
It only has two leaves, which are kept for the rest of its life. Two huge, ribbon-shaped leaves that grow steadily from the base while tapering off at the tip. The leaves can be over four meters long, spreading and wrapping around the stem, creating a shaded area below.
A Welwitschia specimen can live for several thousand years, according to estimates, and although there are other plants with greater longevity, these renew their leaves from time to time. This makes Welwitschia not only one of the most fascinating plants, but also the species with the longest leaves.
Heiress of a strange lineage
Contrary to what it may seem at first, Welwitschia is not an angiosperm, that is, it is not related to flowering plants, but is actually a gymnosperm , closer to ephedras, araucarias, cypresses or yew trees Although it is such a particular and exceptional species that it forms its own botanical family and order, without another closely related species.
The lineage to which Welwitschia belongs is ancient, many researchers consider the species to be a living fossil. Your genome is highly redundant. It is estimated that a duplication of the entire genome occurred about 86 million years ago, and a second duplication between 1 and 2 million years ago. However, many of these duplicate genes are also silenced.
The great longevity, as well as the great tolerance of the plant to thermal and hydric stress and to the low concentration of nutrients, are sustained by these genetic traits. Specifically, due to these changes in the number of copies of genes, and particularly those that control cell growth, differentiation and metabolism. Furthermore, the silencing of redundant genes makes it possible to reduce the metabolic cost of maintaining such a huge genome.
All this makes Welwitschia a potentially immortal plant, but not invulnerable.
What is its conservation status?
Although this species is not included in the catalog of the International Union for Conservation of Nature (IUCN), the expected effects of anthropogenic climate change on the habitat may put Welwitschia at serious risk of extinction. In addition, their populations are highly fragmented, a circumstance that, given the harsh conditions of the desert, favors isolation and prevents pollinators from performing their function optimally.
A group of researchers led by Pierluigi Bombi, from the Terrestrial Ecosystem Research Institute of Monterotondo, Italy, recently carried out a study in which, based on IUCN criteria, they classified the species as “endangered”.
References:
Bombi, P. et al. 2021. Very high extinction risk for Welwitschia mirabilis in the northern Namib Desert. Journal of Arid Environments, 190, 104529. DOI: 10.1016/j.jaridenv.2021.104529
Henschel , JR et al. 2019. Roots point to water sources of Welwitschia mirabilis in a hyperarid desert. Ecohydrology , 12 (1), e2039. DOI: 10.1002/eco.2039
Ruhfel, B. R. et al. 2014. From algae to angiosperms–inferring the phylogeny of green plants (Viridiplantae) from 360 plastid genomes. BMC EvolutionaryBiology, 14(1), 23. DOI: 10.1186/1471-2148-14-23
Wan, T. et al. 2021. The Welwitschia genome reveals a unique biology underpinning extreme longevity in deserts. Nature Communications, 12(1), 4247. DOI: 10.1038/s41467-021-24528-4
Yao, Y. et al. 2019. Liquid Collection on Welwitschia-Inspired Wavy Surfaces. . DOI: 10.48550/ARXIV.1911.10603
