Scaring Up "Ghost Plants" in Mexico

William Cocke
for National Geographic News

March 17, 2004

The ghosts of lost plants haunt Mark Olson. As a biologist at the
Universidad Nacional Autónoma de México in Mexico City, Olson
specializes in plants of the dry tropics. Seasonally dry habitat, which
includes forest, savannah, and spiny desert, comprises more than 75
percent of the tropics.

Olson is troubled that more than half of 317 species of neotropical plants described by botanists are known from just one or two collections. Many times, these collections are dated or vague in their descriptions.

"When you know a plant from just one collection, all you know about it is that it exists … and where it was found, but we can't say much about it," Olson said. "We don't know if it's very rare and very restricted or if people have just been overlooking it."

Olson's concern is not limited to New World plants. All across the globe, plants that have been found, filed away, and forgotten are his passion. They are what drive him to explore some of the most remote—and dangerous—spots on the planet.

"The search for and rediscovery of these species include some of the highlights of my fieldwork—and some of the most heartbreaking—when it becomes clear that a species has probably become extinct," he said.

A Passion for Plants

Growing up near Lake Tahoe in the California town of Grass Valley, Olson was fascinated by the natural world. He knew early on that he wanted to be a biologist.

During a post-high school turtle-tagging expedition to Costa Rica, Olson discovered a love for fieldwork. Less appealing was one collection method for zoological work.

"We put tags on the sea turtles," Olson recalled, "[and the tags] crunched through their flippers. They gasp and wince and bleed all over the place. Obviously it hurts them."

Plant collecting—a branch snipped here, a leaf pressed there—seemed less harmful to him, with lower impacts on sensitive populations. Besides, he said, " I thought plants were more interesting." A budding botanist was born.

Olson received his undergraduate degree in botany from the University of California, Santa Barbara, in 1992. After working in the university's herbarium for a year, he spent a year as a Rotary scholar in Italy, learning to draw and exploring the lakes around the northern Italian town of Mantova.

Olson applied to graduate school at Washington University in St. Louis, also home to the world-renowned Missouri Botanical Garden. He earned his Ph.D. in 2001, writing his dissertation on the Moringa family, an assortment of often strange plants that include trees, shrubs, and herbs.

Studying the 13 morphologically distinct Moringa species fueled his passion for the bizarre plant forms found only in remote non-rain forest tropical landscapes. He also discovered that some Moringa species were essentially lost to science. One, Moringa arborea, had been seen just twice.

The Long-Lost, the Living Dead

In 1998, thanks in part to a grant from the National Geographic Society Committee for Research and Exploration, Olson traveled to the Mandera District in extreme northeast Kenya—then a dangerous no-man's-land where Kenya, Ethiopia, and Somalia intersect—to search for this lost species. Adding to his difficulties, previous botanists had identified only a single M. arborea tree. At the time, it didn't have any leaves.

"I was thinking, How am I going to find this single tree?" Olson recalled. "Usually [plants] grow in populations. Occasionally … a seed will get blown off … or a plant will establish and grow way out from [the others] … and the real population was for me unknown."

Olson was lucky. In a small limestone canyon, near where the M. arborea was first discovered, he came upon a whole population in full bloom. He collected a couple of seedlings. "I took one back to St. Louis, where it's … made plenty of leaves," he said.

In Madagascar, Olson was less fortunate. Along the island's west coast, local people plant the massive, 60-foot-tall (18-meter-tall) Moringa hildebrandtii ceremonially—often near gravesites. Wild populations were unknown, but were thought to exist on the island's central west coast.

Olson and a Malagasy colleague searched in vain for wild M. hildebrandtii. "We suspect that what has happened is … it's been reduced to a very tiny population or it was extirpated from the wild a long time ago," he said.

"It's been preserved in indigenous horticulture but not in the wild," he said. "So it's sort of a living dead species. We don't know where it's from really. We don't know what its interactions were."

Pedilanthus and People

In Mexico, Olson has had similar mixed results searching for lost slipper spurges, or Pedilanthus, a genus of small leafy shrubs and trees with flower clusters that resemble everything from shoes to ducks. Mexico is slipper spurge central, the only country where all 15 or so species are found. For the last year and a half, Olson has (again with National Geographic Society funding) scoured the country from Baja California to Yucatán to the Guatemalan border.

Pedilanthus pulchellus was first described in 1917 growing on a single mountain, Cerro Espino, in southern Oaxaca. "[We] reasoned it had to be on the very highest peak of this one mountain," Olson said.

"We made the ascent and there it was, growing right on top of the mountain as it has been since 1917, the last time it had been seen. And [it was] just [because] no one had ever climbed the mountain again." Olson has since recommended conservation measures to protect this rare microendemic plant.

For another slipper spurge, Pedilanthus tomentellus, it's probably too late. Known since pre-Columbian times for its yellow latex and laxative properties, P. tomentellus is grown ornamentally and in herbarium collections.

It was seen growing wild as late as the mid-1980s. "When you go back … the people remember it being there," Olson said. People who recall the plant tell him they ripped it up to sow corn. "You're getting there at the moment of extinction, because it is still living in people's memories. But the plants aren't there anymore. It's gone from the wild."

Such ghost plants, which survive only in cultivation, make Olson wonder about other species yet to be discovered. " That's sort of the cruel joke of being a biologist," he said. " [Plants are] disappearing very rapidly … that's what's going on."

"A lot of people don't realize that where they live is actually very, very special," he said. "And that's … something we always try to tell people in the field." With biologists like Olson continuing the search for lost species, perhaps more people will find that plants also deserve their place in the world.

For more on Mark Olson and plants, scroll down for related stories and links.