Torn to ribbons in the desert: botanists puzzle over one of earth's oddest plants

Science News, Oct 27, 2001 by Susan Millus

Judy Jernstedt admits that the plant she went almost halfway around the world to see looks "like a pile of trash."

That's part of its charm. And to be fair about it, that's not the only way that Jernstedt describes the remarkable Welwitschias of southwestern Africa. "They look like giant spiders creeping over the hills," she says.

The stem of an adult plant--Jernstedt compares it to an upside-down traffic cone--typically has just two long, straplike leaves. They never fall off, and a plant can live for 1,500 years. In the plant's native Namib and Mossamedes deserts, wind thrashes the leaves into ribbons. The strips get pretty tangled as the centuries go by.

Now a plant morphologist at the University of California, Davis, Jernstedt first heard about Welwitschia during her student days. "We were told how peculiar they are," she reminisces. Some 140 years after the discovery of Welwitschia, taxonomists haven't been able to agree on where to place this species in the tree of life.

Botanic gardens around the world now grow specimens, but they barely amount to toddlers in terms of the species' life span. "I've always wanted to see Welwitschia in the wild," says Jernstedt. Two years ago, when planning a trip to Africa, she decided to do something about this goal.

She described the results of her adventures to the annual meeting of the Botanical Society of America in Albuquerque, N.M., last August.

Jernstedt isn't the first botanist to be bedazzled by Welwitschia. "It is out of the question the most wonderful plant ever brought to this country and one of the ugliest," a curator at the Royal Botanic Gardens in Kew, England, commented in 1863. Two plant explorers independently discovered the species in the early 1860s. One was trekking in what's now Namibia, and the other, in Angola. The genus name Welwitschia comes from the explorer of Angola, Friedrich Welwitsch, and taxonomists have institutionalized the astonishment of the Welwitschia discoverers by settling on the species epithet mirabilis.

The adult plant's stem ends in a shallow bowl that can reach the size of a hubcap. From the bowl's rim sprout the leaves that the desert winds eventually convert into a shoulder-high mass of snarled curlicues. An African name for the plant has been translated "long-haired thing."

The plants bear arrays of small cones instead of flowers. Unlike many plant species in which male and female organs arise in the same individual, Welwitschia separates the genders. An individual's cones carry either male reproductive parts or female ones. Droplets of sweet liquid draw flies to pollinate the plant.

The cones led botanists to first place the species with the gymnosperms, the broad group that includes conifers, ginkgoes, and seed ferns. However, cellular details of Welwitschia's reproduction echo processes observed within flowers. Also, the female cones sport small, leaflike bracts that might be considered a distant relative of flower parts.

Could Welwitschia represent a relic of some lineage between gymnosperms and flowering plants? Until recently, the reigning theory was that Welwitschia and its next of kin are the closest living relatives of the flowering plants, says Michael J. Donoghue of Yale University. Some molecular data, however, now suggest that Welwitschia nests within the conifers.

Michael Frohlich's research team at the University of Michigan in Ann Arbor, for example, is working to clarify the plant's history by comparing several genes in Welwitschia with some in other oddball cone bearers and flowering plants.

"At the moment, I would just say that there is great uncertainty, which enhances the great, mystery that has always surrounded these plants," Donoghue concludes.

Part of Welwitschia's fascination, Jernstedt says, comes from the puzzle of its leaf formation. Carbon-14 dating has put the age of two of the plants out in the Namib Desert at roughly 1,500 years and counting. Even over centuries, the plants don't shed their leaves. The single pair per plant endures by growing much as hair does. The tips may split and break away, but new tissue arises from the base.

Such perpetually growing leaves are rare, explains one of Jernstedt's UC-Davis colleagues, molecular biologist Neelima Sinha. Most plants sprout leaves that can extend only to a predetermined limit. Just the tip of the plant keeps generating new tissue.

Welwitschia plants start out with a growing tip, too, but it dies off. To find the genes that control such growth patterns, Sinha and one of her students, Thinh Pham, have been studying Welwitschia seedlings in a laboratory at UC-Davis.

Jernstedt wanted to see the centuries-old Welwitschia leaves in all their tattered glory. She started her quest by searching the scientific literature and soon discovered that Dieter J. von Willert of the University of Muenster in Germany has been publishing research papers on the plant for decades.

One of von Willert's papers particularly intrigued Jernstedt. In 1993, he reported that contrary to what Western botanists have believed for more than a century, Welwitschia in the wild sometimes grows one or two extra leaves. Seeing a wild Welwitschia would be exciting, but the chance of observing an extra-leafy one was irresistible to Jernstedt as a plant morphologist. It would be the botanical equivalent of finding mice with six legs.