Nature’s Pharmacopeia: A World of Medicinal Plants

Book Preface

Of all the diverse life-forms on the planet, plants have the unique ability among multicellular organisms to generate their own energy by capturing the energy of sunlight in chemical bonds. To carry out this feat, the green lineage has evolved complex biochemistries to sustain growth and reproduction fed only by air, water, earth, and light. Setting out roots to capture valuable water and minerals, unfurling leaves to claim a share of the sun, the plant form might seem well suited to a solitary existence. Yet the realities of life for plants in all the ecological niches in which they grow require them to compete for such limited resources with other organisms and to resist the assault of those species seeking to consume them. And while animals such as insects and mammals can walk, fly, bite, and chew their herbaceous prey, plants cannot flee their animal attackers. Rather, plants in fields and forests around the world have developed over millions of years highly sophisticated mechanisms to safeguard their bodies from herbivory.

Among the strategies plants use to deter attack is the channeling of their internal metabolisms to produce an enormous variety of chemical compounds that can interact specifically with animal physiology. Indeed, multiple families of plants generate compounds at great energetic cost that have little or no activity within their own cells, compounds that they accumulate or exude but are not critical for life. These molecules—including plant toxins—gave their producers an edge by allowing them to resist the rampages of insect pests just slightly better than their neighbors. In response to the incapacitating potential of plant poisons, the animal herbivores evolved resistance to these compounds, pressuring the plants to develop higher concentrations and greater diversity in their chemical weaponry. Thus this interspecies arms race has continued for millions of years, with trees, flowers, and grasses of all varieties producing a bewildering assortment of alkaloids, terpenoids, phenolics, and glycosides. These compounds can function as nerve poisons, steroid hormone mimics, heart toxins, and neurotransmitter-like molecules in animals from caterpillars to grazing livestock.

As humans formed societies and migrated into new areas, they learned of these poisonous plants and taught their children which leaves not to touch and which fruits never to taste. They also recognized that certain plants and plant parts were useful for flavor and aroma and, occasionally, for special medicinal or spiritual purposes. Shamans and priests developed a discipline in which plants were integral to the individual’s state of health and the community’s sense of purpose. At the appropriate dose, some plant poisons can generate profound physiological effects on humans by relieving pain, altering the mental state, and intensifying the senses. The wise practitioner held responsibility for distinguishing the desired plant from the deadly and the effective dose from the lethal.

Through the ages, peoples have harvested and cultivated plants that could serve to heal them, numb them, and stimulate them. Certain plant medicines, such as digitalin, a foxglove-derived heart drug, fell under the purview of doctors and pharmacists; others, such as cocaine and marihuana, drew strict regulation, and their possession was criminalized in modern times. Meanwhile, plant preparations in the form of coffee, tea, and chocolate have served as foundations of social and economic life for nations around the world for centuries.

The story of these plants and the compounds they produce is one that spans the globe and reaches back millennia. It encompasses some of the simplest life-saving power revealed to humankind and some of the most deadly chemicals ever uncovered. Wars of the pen and sword have been conducted to control these potent plants, and paintings and prose have been dedicated to extol them. The story of medicinal plants touches the best and worst moments of our civilization. Ultimately, it is a story of these plants’ capacity to influence profoundly the human experience and to convince us to value them, cultivate them, and spread their seeds, and of our ability to learn from, profit from, and manipulate nature.