Walter Lewis Botany

Ethnobotanist: World expert on airborne and allergenic pollen and famous for targeting medicinal plants in the tropical rain forest.

"Do what you enjoy and go where your heart takes you."

The Story

Holding his half-full gourd of “chicha,” Walter Lewis smiles, wishing he didn’t have to drink another drop. It tastes so sour, like a combination of yogurt, warm beer and mashed potatoes. But the headman — the apu of the Achuar Jivura village in the Peruvian Amazon jungle — is looking him right in the eye. To refuse this friendship ceremony drink would be an insult to his hosts.

Lewis takes another look at the yellowish liquid in his gourd. He knows that Achuar women make chicha by chewing a kind of cassava root and spitting it into a huge bowl. Then they let it stand for a while to ferment. The air in the open hut is wet and hot. Lewis feels his shirt stick to the sweat on his back as he turns to glance at his wife, Memory, sitting among the women just outside the men’s circle. A smouldering cooking fire gives everything the smell of smoked fish. The forest outside is alive with shrieking jungle birds while inside the hut, pet parrots, monkeys and dogs squawk and bark. A crowd of gawking, naked children surrounds the Lewises. “We are the zoo,” thinks Lewis as he takes a final sip of the brew like a good ethnobotanist.

The Lewises have travelled to the Peruvian jungle in search of plants that might yield new drugs. They are ethnobotanists and they specialize in communicating with native peoples around the world to learn about their traditional medicines. Mariano, the headman, is telling Walter about the healing powers of a certain plant whose roots are used to help women through the final stages of childbirth.

While Walter is talking to Mariano, Memory notices a big grin on the face of an old woman in the back row. In Achuar culture, women do not sit with the men but have their own special area within the hut. Memory quietly goes to talk to the old woman, who turns out to be Mariano’s auntie. She takes Memory outside to show her the plant Mariano is talking about, all the while telling her how men don’t know much about this medicine, since it’s used strictly by women. When Memory sees the plant, she learns that it’s not the root the Achuar use but the leaf. On closer inspection later, Walter discovers that it’s not the leaf that has the medicinal quality but an ergot-like fungus growing on the topmost leaves of the plant.

The Lewises credit many of their discoveries to the way they work as a team. If Walter had been in the jungle on his own, perhaps he never would have discovered this medicine. As a man he would probably not have talked to the women of the tribe, and he would have embarked on a futile search for the active ingredient in the roots of the plant.

As A Young Scientist...

When Walter was 12 his dad asked him what he wanted for his birthday. The Lewis family lived in Victoria, British Columbia, and Walter was fascinated by an uncle who had a plant nursery in the countryside. Walter told his dad he’d like a greenhouse for his birthday, and his father gave him one. It was made of wood and glass and was about three metres long and two metres wide, with planting benches on each long wall. Walter’s uncle taught him how to grow roses from cuttings. The next summer Walter began selling his roses in Victoria.

His mom and dad wanted him to become a dentist. Walter went to Victoria College (which later became the University of Victoria) to study toward dentistry, but he took extra botany courses on the side to satisfy his curiosity about plants. After second-year university he announced to his parents that he would become a botanist, not a dentist.

The Science

Ethnobotany is the study of plants by obtaining information from people around the world. The Lewises specialize in discovering new drugs extracted from plants used in folk medicine by native tribes in South America and other tropical parts of the world.

Three-quarters of all modern drugs come directly or indirectly from plants used in folk medicine. The Lewises are desperately trying to catalogue the wide variety of plants used by tropical rainforest cultures before the forests are chopped down. They have collected thousands of plants and found dozens of traditional medicines. These include a wound-healing tree sap that helps cuts and scrapes heal 30 percent faster. Other plants treat malaria, hepatitis, diarrhea and more. In 2003 Walter Lewis and his colleagues at Washington University in St. Louis submitted an anti-malarial patent based on their collaborative research with Peruvian natives, who also own part of the patent. Meanwhile, Memory Elvin-Lewis collaborated with Peruvian physicians and U.S. researchers on studies demonstrating the value of traditional hepatitis remedies.

The tropical jungles where most of these plants grow are disappearing. At the same time, the people who know how to use these plants are becoming more “Westernized” (steeped in the culture of North America and Western Europe) and are losing their traditional culture and knowledge of the forest. The Lewises are trying to talk with these people before it is too late. The plants they discover may become widely used miracle drugs of the future.

Achuar ethnobotany. Click to enlarge.

1. The hut: The Achuar hut sits in a clearing in the forest. It’s about 12 metres long and seven metres wide. Several families live together inside. Unmarried and widowed women live at one end. Meetings are held at the other end around a Snake Stool, where the headman or apu sits. Open fires burn on the floor and the smoke goes out a hole in the roof.

2. An Achuar elder: Now dead, this wise elder taught the Lewises much about the medicinal plants of the Achuar.

3. Gourd with holly leaves: Each morning, before dawn, the Achuar men drink guayus, a very strong, pleasant-tasting caffeine drink made from holly leaves. Each man usually drinks about a litre; within 45 minutes he vomits about half of it back up. The vomiting is not caused by the guayus but is a custom of the tribe. When boys reach maturity, they join the men in the morning ritual of drinking and regurgitating guayus. It is considered an honour, and boys look forward for years to this right of passage. The Lewises do not know why the tribe has developed this custom. Perhaps vomiting every morning is a healthy ritual in a jungle environment where many deadly parasites thrive.

4. Methylergonovine: When Walter Lewis returns from the jungle to his university laboratory, he uses chemical identification techniques to determine the molecular structure of the active ingredients in the medicinal plants he brings back. This is a typical diagram of a molecule similar to the active ingredient in the ergot-like fungus the Lewises found growing on a plant used by Achuar women to aid in childbirth.

By observing and talking to native people from India, Africa and the Americas, the Lewises have learned how some trees cause allergies. They have been called upon to advise cities in their tree-planting policies. The Lewises have also studied the use of chewing sticks by hundreds of millions of native people around the world instead of toothbrushes. One example is the bark of the neem tree, which, when chewed, provides anti-microbial and anti-inflammatory effects that can reduce gingivitis (gum disease). However, the couple report that neem bark also contains chemicals that could cause cancer. Memory Elvin-Lewis, commenting on the safety of natural herbal remedies in her 2001 landmark review of herbal medicines in the Journal of Ethnopharmacology, says, “The notion that ‘natural is safe’ has little meaning in reality unless, of course, one puts into the same context the idea that ‘pharmaceutically derived’ is not always totally beneficial.” The Lewises like to point out that naturally occurring medicines can be very beneficial, but they must be treated with the same caution and respect as conventional medicines from commercial drug companies.

The Lewises have achieved their goal as ethnobotanists by cataloguing the medicinal plants of the world in an 800-page book, Medical Botany: Plants Affecting Human Health. While they started by observing and recording how indigenous cultures used medicinal plants, eventually their research shifted: they began working with chemists and pharmacologists to develop new medicines from the plants they discovered. “Things have changed,” says Walter Lewis. “Everyone is concerned with intellectual property when you collect a plant. If you use native know-how, you have to pay them upfront for the privilege of collecting specimens even during the development phase.”

The Lewises now spend the greatest percentage of their time negotiating among native peoples, the university and pharmaceutical companies. They want to get marvellous new drugs to cure diseases such as hepatitis, tuberculosis and malaria, but they also want the native people to be adequately compensated and to retain part ownership of patents and the medicinal knowledge of the plants their tribes have used for centuries. “We invent the chemistry and pharmacology to say precisely what is going on with a medicinal plant,” says Dr. Lewis, “but the native people own the knowledge of the medicinal qualities of their plant.” But large drug companies wish to benefit commercially from these new medicines, too. It’s a delicate balance and takes a lot of time.

Twenty years ago, Western ethnobotanists like the Lewises could find a remote rainforest tribe, learn its herbal remedies and simply take whatever plant material they wanted back to their laboratories for study. Today, things are different. The potential commercial value of drugs derived from jungle herbal medicines is in the hundreds of billions of dollars. Realizing this, indigenous peoples have formed organizations to protect their wealth of plant knowledge. The Lewises now must arrange their explorations with a Peruvian group called the Confederación de Nacionalidades Amazónicas del Perú (CONAP), which represents 18 Amazonian tribes. They have to negotiate payment for doing research, and they must agree to share any wealth arising from discoveries. The Lewises also want to help protect the tribal knowledge, so they now encode data and keep plant names secret to ensure nobody steals that knowledge.

There are other ethical dilemmas in the rainforest. “If you discover that one tribe has found a cure for some disease, can you ethically tell a neighbouring tribe which plant it is?” asks Dr. Lewis. He will not give out this information, but he will name a contact person in the other tribe.


In the Peruvian jungle, the Achuar have shown the Lewises a plant they use to treat “the frightened people.” The Lewises do not know what the Achuar mean by this, but they feel that if this mystery could be solved, a new drug for anxiety or some forms of mental illness might be discovered.

Explore Further

Memory Elvin-Lewis, “Should We Be Concerned about Herbal Remedies?” Journal of Ethnopharmacology, no. 75, 2001.

Walter Lewis and Memory Elvin-Lewis, Medical Botany: Plants Affecting Human Health, John Wiley & Sons, 2003.

Walter Lewis, et al., “Ritualistic Use of the Holly Ilex Guayusa by Amazonian Jivaro Indians,” Journal of Ethnopharmacology, no. 33, 1991.

Introduction to ethnobotoany  - series of educational videos

Career Advice

So You Want to Be a Ethnobotanist

The Lewises enjoy their work because they are often forced to learn a lot of new things. Bringing a drug out of the rainforest requires many skills. Besides a basic knowledge of biology, medicine and chemistry, the Lewises must be politicians, ethicists and entrepreneurs. There are legal aspects of intellectual property law that must be learned, as well as plant pathology (diseases of plants), genetic engineering, plant breeding, pharmacology (the study of drugs), viruses, microbiology and anthropology. “You learn to stretch your knowledge in every area,” says Dr. Lewis. Because of the many extra things you must learn along the way “it takes you all your life to get where you’re going,” adds his wife, Dr. Elvin-Lewis. She cautions that there are many 18-hour days and full seven-day work weeks, but she loves the travel and the excitement of living in the jungle with native people. The couple’s greatest challenge is finding enough money to bring these very valuable drugs out of the rainforest. “I feel very committed to the wonderful indigenous people we’ve been privileged to work with, and the trust they have in us so the world can benefit from their knowledge,” says Dr. Elvin-Lewis.

Walter Lewis enjoys the fieldwork, too. “It’s ‘work’ in a sense,” he says, “but I find it relaxing and enjoyable. I’m fortunate that my work is my play.” (Collecting plants is his hobby.) The things he dislikes about his job are report writing, committee meetings and administration. His advice to young scientists: diversify and explore many avenues. Don’t be too narrow in your studies.

The Person

June 26, 1930
Ottawa, Ontario
St. Louis, Missouri
Family Members
  • Father: John Wilfred
  • Mother: Florence
  • Spouse: Memory Elvin-Lewis, Professor of Biomedicine, Washington University
  • Children: Memoria; Walter H., Jr.
Congenial, determined
Favorite Music
Andean flute music
Other Interests
Gardening, antiques, family, travel
Professor of Biology, Washington University, St. Louis, Missouri
Biology Department, Washington University, St. Louis, Missouri
  • BA (Honours) UBC, 1951
  • MSc (Botany and Biology), UBC, 1954
  • PhD (Biology), University of Virginia, 1957
  • Post doctoral work at Kew Gardens, London and at the Swedish Academy of Sciences, Stockholm.
  • Guggenheim Fellowship, 1963
  • DuPont Fellowship, 1953
  • Fellow of the Linnean Society of London, 1983
  • Fellow of the Royal Geographical Society, London, 1987
  • Martin de la Cruz Silver Medal (Mexican Academy of Traditional Medicine), 2000
  • Janaki-Ammal Medal (Indian Ethnobotany Society), 2004
Walter H. Flory who was his thesis advisor for his PhD.
Last Updated
May 15, 2020

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question #2996

Can any plants regenerate after they are totally dried - I don't mean somatic embryogenesis: can the actual dried leaves regenerate, after they are totally dried [land or water plants]?

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