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Welwitschia mirabilis

A large specimen
Pam looking at a
a large male specimen
Largest Welwitschia mirabilis
The oldest and biggest
Welwitschia mirabilis

Welwitschia is found in the coastal desert of Namibia north from the Kuiseb river which reaches the sea at Walvis Bay, to the northern border. Welwitschia is not quite endemic to Namibia. There are small populations in the south western coastal strip of Angola as far north as the Nicolau River. It is believed from recent genetic studies that the plant has been here almost unchanged for over 100 million years.

The 'Welwitschia drive' in the Swakop valley area of the Namib-Naukluft national park is the most famous area for these plants. This specimen (at right) is locally reputed to be about 1500 years old and is one of the largest known. Other estimates give ages up to 3000 years. The populations along the D2303/D2342 between Mile 108 on the coast and Uis are at least as impressive and much larger in numbers.

Welwitschia mirabilis

Welwitschia grow in areas of extreme aridity, with total precipitation much less than 50 mm. per annum. Most of this is in the form of fogs, which cover the area quite often, as warm south Atlantic air crosses the cold Benguela current off shore, causing the water to condense. We experienced several morning fogs during our trip. These caused sufficient moisture to reach the ground to form a very thin damp crust on the sand. Welwitschia are phreatophytes, that is they have very deep roots which reach underground water. They often occur along the courses of spate rivers. Obviously there is water deep underground or the plants can survive on the minimal moisture from the fogs.

Two leaves of Welwitschia mirabilis
The two leaves on a
juvenile plant.
Two leaves of Welwitschia mirabilis
The two leaves on a
mature plant
Tattered leaves on Welwitschia mirabilis
Tattered leaves on a
mature plant
Ribbed leaf of Welwitschia mirabilis
Strongly ribbed leaves
of a mature plant

Welwitschia have only two ribbed, strap like leaves, which grow continuously from the trunk. The 'juvenile' at left is probably more than 100 years old but still show the leaves more or less entire. They become frayed into many ribbons by wind and the ends become tattered as can be seen in the mature plant. Some parts may die back or be lost entirely.

Welwitschia is a Gnetophyte gymnosperm (The gymnosperms consist of the gnetophytes, cycads, ginkgophyta and conifers) although it has many morphological similarities to the angiosperms - flowering plants - and was for some time considered to be a basal angiosperm. It is now considered to be most closely related to the conifers. The similarities of flower structure to the angiosperms is now considered to be convergent and does not imply ancestry. It is certainly not a succulent and has few of the common adaptations to desert life.

Male flowers
Male
'flowers'
Female flowers
Female
'flowers'
Male plant
Male
plant
Female plant
Female
plant

Welwitschia are dioecious, that is they have separate male and female plants with cone-like 'flowers' which produce winged seeds. The seeds are large and heavy and are not dispersed by wind over any distance. Recent studies show that populations within 20 km of each other are genetically isolated. Pollination is by flies. The Welwitschia bug, Odontopus sexpunctatus feeds on the sweet, nectar-like substance on the 'flowers' but is not thought to be the pollinator.

Although seeds germinate freely in cultivation, the local conditions are such that natural germination is very rarely successful and it is clear that there have only been a few periods in the last millenium when plants have become established. Clear age cohorts can be seen in most populations.

References

K. M. Jacobson, and E. Lester A First Assessment of Genetic Variation in Welwitschia mirabilis Hook Journal of Heredity 2003:94(3)

Bornman CH, Elsworthy JA, Butler V, Botha CEJ, 1972. Welwitschia mirabilis: observations on general habit, seed, seedling and leaf characteristics. Madoqua. 1:53-66.

von Willert DJ, Wagner-Douglas U, 1994. Water relations, CO2 exchange, water use efficiency and growth of Welwitschia mirabilis Hook. f. in three contrasting habitats of the Namib Desert. Bot Acta. 107:291-299.

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