In the winter of 1535-36, French explorers were ice-bound in their ships on the St. Lawrence River. Then something frightening started to happen. Purple blotches erupted on their skin. Their legs swelled, and their gums and nails began to bleed. A disease had set in, and it was spreading. Many became too sick to move. Women from a local tribe offered one of their traditional remedies: Tea made from the bark of the white cedar tree. click on each image to enlarge Two signs of scurvy Source: NIH Soon the men's symptoms disappeared, and they were fully recovered. The explorers had no idea what had made them sick—or why they got well. We now know that they suffered from scurvy, a disease caused by vitamin C deficiency. The cedar bark contained enough vitamin C to save them.

Nearly 270,000 known species of plants—and many that remain undiscovered—play a starring role in our lives. They give us food. They add beauty. They even keep us alive, absorbing harmful carbon dioxide from the atmosphere and supplying the oxygen humans and animals need to breathe.

Plants are also nature's medicine. Studies say that between 25 percent and 50 percent of all medicines prescribed in the U.S. today come from plants—or are based on chemicals found in plants. According to the World Health Organization, nearly 70 percent of the Earth's 6.2 billion people rely on plant-based traditional medicine to relieve pain, to heal wounds, and to prevent or cure disease.

Plants are also nature's medicine. Studies say that between 25 percent and 50 percent of all medicines prescribed in the U.S. today come from plants—or are based on chemicals found in plants. According to the World Health Organization, nearly 70 percent of the Earth's 6.2 billion people rely on plant-based traditional medicine to relieve pain, to heal wounds, and to prevent or cure disease.

Plants lay the foundation for some of our more remarkable prescription medicines:

click to enlarge	The flower of purple foxglove contains digitalis, which helps the human heart function normally. It is one of the most commonly prescribed drugs in the world. Traditional healers in 18th-century England used an herbal tea with foxglove; modern doctors based the present-day medicine digitalis on their recipe. Photo source: The Environment & Heritage Service, Northern Ireland
click to enlarge	Paclitaxel from the Pacific yew tree, which grows in the northwestern U.S., fights the growth of malignant cells found in cancer. Its discovery showed modern scientists a new way of preventing the spread of cancer cells: by stiffening them and making it impossible for them to reproduce. Click to learn more about the challenge of balancing environmental and health concerns. Photo source: USDA
click to enlarge	Poppy flowers, native to South America's Andes Mountains, produce opiates, or chemicals that block pain. Photo source: Chemical Heritage Foundation
click to enlarge	Quinine from the bark of a Cinchona tree destroys parasites that cause malaria, the world's deadliest tropical disease. In the mid-17th century, local people in what is now Peru gave quinine to deathly ill Spaniards. Find more information about quinine, the Cinchona tree, and malaria. Photo source: Southern Illinois University

Every part of a plant—the flowers, roots, stems, branches, leaves, seeds, and bark—can have medicinal properties. Steeped in hot water, they make tea. Ground up, the powders are taken orally. Extracted, ointments and oils are rubbed into the skin to deliver the medicine transdermally.

Collecting plants for medicinal use is one of humankind's oldest professions. Written records about medicinal plants date back at least 5,000 years to the Sumerians. Even before that, cave dwellers used germ-killing moss to heal cuts.

George and Martha Washington's drugstore outside of Washington, D.C. Source: Stabler-Leadbeater Apothecary

George Washington or his doctors regularly rode the 13 miles on horseback from Washington, D.C., to the Apothecary in Alexandria, Virginia, to pick up medicinal plant remedies.

Throughout history, whenever people from different cultures met, plants were among the first items they traded. The medicines of two ancient cultures—the Chinese and Indian—are still going strong and have made their way into modern science.

Today chemicals still help scientists create new medicines. Researchers spend a lot of time looking for a plant's "lead molecules" which they can copy or modify to create synthetic versions.

Unlike animals and people, plants can't run away when faced with danger. They also don't have eyes or other sensory organs to tell them trouble's coming. So plants have developed an arsenal of bioactive chemicals to fend off microbes, insects, and animals. Many of these same chemicals are bioactive in humans.

Plants even use chemicals to communicate. In one lab experiment, plants that had no contact with a virus but did have contact with other plants in the same room that were being attacked by the virus began to pump out defensive chemicals. The only possible explanation is that the plants communicated via chemical signals.

Tropical rainforests, which swarm with microbes and insects, rank high among the world's bioactive hot spots. The plants that grow there produce huge amounts of bioactive chemicals to protect themselves. So when we destroy rainforests, we also wipe out thousands of potential medicines. And whenever we ruin any natural habitat—by clearing forests, paving over fields, polluting air and water—we risk the same kind of destruction.

Half of the 270,000 known plant species on Earth are endangered, with more than 10 percent threatened with extinction. Last year, the journal Science reported that we could lose closer to 30 percent.

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