The Horridge Conservatory is fortunate to have a specimen of a weird and wonderful plant: Welwitschia. (Thank you, Arielle!) Mirabilis is the only species in the genus and Welwitschia is the only genus in the family Welwitschiaceae. It is native to the Namib Desert on the coast of the Atlantic Ocean in Namibia and Angola.
What makes it so unusual? An adult Welwitschia consists of only two leaves, a stem base and roots. Its two permanent leaves are the original leaves from when the plant was a seedling– they continue to grow and are never shed. Those two leaves grow from a basal meristem in the plant’s terminal groove. They eventually grow to a length of 2 – 4 meters and become split, frayed and shredded into several well-separated strap-shaped sections which lie on the ground. This gives the appearance in older plants of having many leaves, but there really are only two.
The stem is low, woody, and obconical in shape. It grows to about 500 mm in height. There are separate male and female plants. Welwitschia produces cones but is not wind pollinated as most cone-bearing plants are. It is pollinated by flies, true bugs, and most commonly, the Welwitschia bug, Odontopus sexpunctatus.
Welwitschia is ecologically highly specialized, and is adapted to grow under arid conditions receiving regular fog. This regular, dense fog is formed when the cold north-flowing Benguela Current meets the hot air coming off the Namib Desert. The fog develops during the night and usually subsides by about 10 a.m The broad, downward drooping leaves collect condensation, which drips down onto the plant’s own root zone. It also has numerous stomata on both leaf surfaces and fog-water is taken up directly through these stomata. The fog has been estimated to contribute 50 mm in annual rainfall! A long taproot reaches deep for underground water in this part of the world which often receives less than100 mm of rain a year.
According to the Wikipedia article “Welwitschia”,
“Although Welwitschia mirabilis is not at present immediately threatened, there being abundant populations over a large area, its status is far from secure; its recruitment and growth rates are low, and its range, though wide, covers only a single compact, ecologically limited and vulnerable area.”
It is interesting that it is possible, and not even terribly difficult, to grow Welwitschia as a house plant. A few Botanical Gardens (but not URI) offer seed for sale on line. The greatest danger to the germinating seeds is fungal infection. A very sandy soil mix helps reduce this risk. There is a great article on germinating and growing Welwitschia at home on the Planzafrica website, as well as information about the discovery of the plant by Friedrich Welwitsch.
Welwitschia mirabilis is thought to live 1,000 years or more!