Unusual and Bizarre Plants - Welwitschia mirabilis
Two leaves in 1500 years!
The natural history of Welwitschia mirabilis reads like the account of an organism quite alien when compared to nearly all of the other plants and trees we are familiar with here on Planet Earth. This plant grows in a hot, very dry desert environment,yet cannot be allowed to dry out. It thrives in unshaded conditions, yet can't take the full sun of Arizona. The leaves continue growing for over 500 years, yet the plant produces only two of them in its entire lifetime. The male structures are like cones or thick upright tassels of flowers, with stamens and sterile pistils, while the female structures are cones similar to those on a pine tree. These facts are just a sampling, as nearly every aspect of this plant, from anatomy to culture, is particularly strange.
Welwitschia was discovered in the Namib desert of southern Angola in 1860 by an Austrian botanist, Friedrich Welwitsch, after whom the plant was named. This fellow didn't have delusions of grandeur; his chosen name for the plant was Tumboa, in honor of the native name for the plant. Specimens have been found that appear to have ages from 500 to 1000 years, and a few accounts claim ages as old as 1500 to 2000 years for individual specimens.
A normal start, but then . . .
Growth of this plant starts with a normal-looking seed, somewhat reminiscent of a large elm seed. The little seedling that emerges is not a strange sight, either. Two cotyledons emerge, followed by two small leaves.. These small leaves grow on to exceed the size of the cotyledons, and then just keep on growing. This growth occurs from the base, not from the tip. Meanwhile, a tap root grows downward. This root can go as far down as 10 feet. For this reason, some people growing this plant from seeds use long pieces of ceramic pipe as pots to grow them in. After the first set of true leaves is produced, a second set of leaf buds appears to form, but these never produce leaves. Instead, they enlarge sideways and all apical growth is halted. What is produced is a meristematic area where new leaf tissue is formed at the base of the existing leaves, and where eventually the flowering or reproductive structures will emerge. The central part, where one would expect a shoot to continue growing, gradually becomes dry and corky.
The evergrowing leaves have pores, or stomata, on both sides of the leaf, unlike "normal" leaves having them only on the undersides. Plus, these stomata open up when fog rolls in, and close in the heat of the day, which is exactly the opposite of what happens in familiar plants we all know and love. These leaves are able to take up moisture from fog through the pores to supplement what meager rain falls in their habitat. The leaves sprawl on the sandy ground, becoming tattered at their ends as they are blown about by desert winds. They do provide some shade for the base of the plant, which provides a small respite from the scorching heat of day.
Welwitschia plants are either male or female, but never both. Both mature male and female plants produce conelike reproductive structures, called strobili (singular, strobilus), but the male ones have stamens producing pollen and the female ones produce the seeds when fertilized (see thumbnail picture above, right, for female plant, picture above, left, for example of male plant). Interestingly, both types of flowers produce nectar to attract pollinators. The most likely pollinator is a wasp, which carries the pollen to the female structures where fertilization takes place.
An origin defying certainty
Welwitschia has been classified as a gymnosperm along with the pines and cycads, but scientists have determined that the vascular tissue (xylem) is typical of that found in the flowering plants, or angiosperms. Plus, the structure of the male flowers is very similar to those on some of the flowering plants, adding to the enigma. At this time scientists recognize only one species of this genus, and perhaps two subspecies or varieties of that species. The plants are protected by law in their native habitat.
If you want to try your hand at growing one of these beauties, here's one place that has them for sale: Living Stones Nursery.
Image credit: Wikimedia Commons
(Editor's Note: This article was published on September 16, 2008. Your comments are welcome, but please be aware that authors of previously published articles may not be able to respond to your questions.)
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