Our lack of understanding when it comes to plants and ecosystem workings shows up in the steady flow of news about environmental crises. Red or brown "tides" of marine algae appear along the Atlantic coast and fish die off. Wildfires engulf Yellowstone National Park or the California hills, destroying forests and homes. Kudzu (Pueraria lobata), purple loosestrife (Lythrum salicaria), water hyacinth (Eichhornia crassipes), and other invasive plants threaten the south, the Everglades, our national parks. Very little of the natural world remains pristine; most of it is now managed. Yet the management proceeds without a sound understanding of ecosystems, often leading to crises. Some of the toxin-producing algae responsible for the fish kills were unknown to science before they bloomed, a phenomenon that seems to be Increasing worldwide. The biological necessity of fire for some ecological communities remains hard for the public to fathom and to apply. And how an apparently innocuous plant can suddenly turn into a multimillion dollar problem weed continues to perplex plant biologists.

Conversely, what we have learned from plant studies has engendered a wealth of tangible practical results, and not just in terms of foods. Plants enter our lives in innumerable ways, a function of their genetic, chemical, and structural diversity. You are looking at a plant product in the form of this page. (Despite the proliferation of electronic communication, readers still prefer the texture and eye-ease of printed paper.) You are also probably wearing plant products in the form of cotton, linen, or rayon, and sitting on or in a structure of wood, perhaps the most prized of plant products. No matter what you last ate, the fuel it is providing your cells to function was originally captured from the sun by a carbohydrate-making plant The spice, color, or flavor of the food no doubt cam from a plant leaf, seed, or oil.

Plant products similarly form the basis of many common, and many unusual, medicines. Long before, Bayer chemists commercially synthesized salicylic acid, the

Electron micrograph of a chloroplast in a leaf cell of Zea mays. Courtesy: Ray F. Evert.

active ingredient in aspirin, Native Americans and ancient Greeks brewed tea from willow bark for pain relief. The plants (Salix spp.) manufacture similar compound that seems to deter some animal and insects from feeding on the plants. Other bioactive plant compounds have found uses as pain relievers and cough suppressants (morphine and codeine from poppies); heart stimulants (digoxin from foxglove); and cancer chemotherapies (vinblastine from the rosy periwinkle and taxol from yew), to name a few. Pharmaceutical companies typically aim to design synthetic ways to manufacture the compounds once they have been identified, but for compounds such as digoxin the plant chemistry has proved impossible to duplicate economically, and cultivated plants are the only source of the drug. In some case the plants themselves haven't been cultivated. A slow-growing Amazonian vine (Chondrodendron tomentosum) remains the pharmaceutical source of tubocurarine chloride, a muscle relaxant and an active ingredient in curare used in surgery.

Several specialties within botany are devoted to understanding the biochemistry and molecular biology of these compounds, and why there is so much chemical variation among plants. Most of these compounds, once thought to be waste products, are now believed to be chemical defenses against herbivore or attractants for pollinators, although the specific function has been demonstrated for few cases. The presence of chloroplasts in plant cells explains some of the most vital (and valuable) plant chemistry. These organelles are the site of photosynthesis and the manufacture of the eight or more amino acids we call essential, because we cannot make them but need them in our diets to build proteins. The creative capabilities of chloroplasts hark back to their origins as bacterial cells, which were engulfed or otherwise entered into a symbiotic relationship with larger cells, leading to the evolution of photosynthesizing plant cells.

Chloroplasts create other interesting products, including ascorbic acid and some of the other vitamins we depend on plants to provide. in some plants, the end product of photosynthesis is not the usual carbohydrate sugar but an alcohol, such as mannitol or sorbitol. These compounds impart sweetness without sugar and are ingredients in sugar-free gums. in other plants, chloroplast enzymes will convert the fixed carbon into fatty acids, which then find their way into the useful seed oils. The final results

Scanning electron micrograph of a spore, Lophocolea heterophylla a "leafy" liverwort from a Wisconsin peat bog. Courtesy: Linda E. Graham.

may be as diverse as olive and corn oils for eating, tung and linseed oils for varnishes and paints, and castor oil for use as a medicinal purge. Of the many underutilized tropical plants, the babassil palm (Orbignyaphalerata) has been eyed as a potential renewable source of oil for fuel--500 trees can produce about 125 barrels of oil a year.

A large number of the plant compounds we have found to be medically or commercially useful fall into a vast class of chemicals known as terpenes. Several Nobel prizes have been awarded for working out the synthesis or structure of this most common and useful type of natural product. All terpenes have as their base a five-carbon unit. By linking and combining these into larger structures, plants create vitamins; steroids (diosgenin from wild yams has been the basis for oral contraceptives); carotenoids, including the yellow and orange pigments that are the basis for fall tourism throughout the Northeast; and solvents such as the familiar turpentine. With subtle changes, plants make very different products: the sap from the para rubber tree (Hevea brasiliensis) yields a terpene polymer with a certain conformation (cis-polyisoprene) that is the source of natural rubber for tires. Another tree (Palaquium gutta) makes a slightly different conformation (trans-polyisoprene) that is good for golf balls. A combination of the two forms in the latex of another tree (Achras sapota) makes chicle, the basis of chewing gum.

Plants polymerize another terpene (carotenoid) into a unique material known as sporopollenin, which is responsible for the spectacular durability of plant spores and pollen grains. The resistance of pollen and spores to acids and the genus-specific sculpturing of their outer sporopollenin wall has made them a valuable and well-represented part of the fossil record. Fossilized pollen has been a primary tool in paleoecology and paleoclimatology, for reconstructing past ecosystems and communities and assessing how they were affected by climate change on otherwise inaccessible time scales, and in archaeology.

Biological and other technologies have broadened still further the diverse uses of plant chemistry. A sampling of some of the applications of plants under investigation or development:

• Fuel. Apart from the familiar fuel sources of wood and coal, other plant products are being tapped for their energy. Ethanol and methanol fuels can be distilled from fermentation of plants such as maize or produced from other biomass. A pilot electricity generator has been designed to run on algae: growing algae consume the carbon dioxide released during combustion; the fuel is provided by cakes of the dried harvested algae.
• Bioremediation. Some plants have evolved in and cope with soils containing naturally high levels of acids or heavy metals, a trait being used to clean waste and mining sites. Plants known as hyperaccumulators may absorb large enough quantities so that the lead, cadmium, or other contaminants may be recovered for other

  A solitary shagbark hickory (Carya ovata) in the winter condition. Courtesy: Ray F. Evert.

  uses by smelting the plants. Fungi and algae, with their large numbers and enzymatic versatility, are also finding applications in biosorption.⁴
• Medicine. The role of plants in medicine is expanding beyond their traditional and continuing role as a pharmacopoeia. The basic similarity of all life chemistry has inspired the test use of plants as manufactories for tumor-attacking monoclonal antibodies or other biopharmaceuticals. Genes for clinically important proteins are engineered and inserted into the plant cells, which can be coaxed to take up and express the DNA. Large amounts of the expressed protein could theoretically then be harvested and extracted from the seeds of the adult plants. Work on fungal pathogens that attack plants has turned up natural bacterial antibiotics that are being tested for use against fungi, such as Candida, that attack humans. Fungi themselves may be a prime source for natural compounds that are active against disease viruses, although biomedicine has virtually overlooked this area until recently. There are almost certainly new natural antiviral compounds to be found in plants as well. Podophyllotoxin, a treatment for genital warts, comes from the May apple (Podophyllum peltatum), and screening programs have recently found anti-HIV activity in several plants, including a vine (Ancistrocladus korupensis) collected from an African rain forest and recognized as a new species in 1991.
• Agriculture. Genetic engineering of plants has taken its place alongside traditional crop breeding as a means of creating plants with novel traits. Most of the major food grains, as well as numerous fruit, vegetable, forage, fiber, oil, and ornamental plants, have been targeted in trials or in commercial development with genes from other species that enhance resistance to diseases, drought, frost, herbicides, or herbivores. Other research is focusing on enhancing the sustainability of crop-plant systems. Understanding and enhancing the complex plant-bacterial processes involved in nitrogen fixation is of major interest and importance.

Even as biotechnologists and botanists are developing new uses of plants, the genetic diversity plant offer as a starting material is being reduced. The loss of

The fungus Penicillium, source of the first antibiotic. Courtesy: Ray F. Evert.

diversity--whether genes, species, or ecosystems--is affecting all groups of organisms, a major concern for biologists. Yet as the National Science Board has pointed out, "much of the diversity of life is threatened by the destruction of plant diversity, because plants provide both food and habitat for other organisms." Conversely, the restoration of plants to an ecosystem can enhance the conservation of other groups of organisms. Plant diversity is furthermore an economic asset: "Crop genetic resources have accounted for about 50 percent of productivity increases and for annual contributions of about $1 billion to U.S. agriculture," according to the Office of Technology Assessment.

Botanical knowledge is therefore crucial to minimizing the global loss of biological diversity. Botanists have key roles to play in broadening the diversity of resources we use-detailed studies of rain forest algae, for example, have never been done, despite their common presence as green films on most trees and the demonstrated value of this group of organisms. Botanists' work on the genetics, physiology, ecology,

White potato (Solanum tuberosum) tubers attached to the underground stem portion of the plant. Courtesy: Ray F. Evert.

and evolutionary history of plants, both in natural and agricultural ecosystems, is also needed for guidance in conservation.

Similarly, botanical knowledge is crucial for understanding and coping with projected changes in global climate. Climate change is only important as it affects the biota, and the foremost biotic impact is on plants and our food supply, a relatively neglected area given its importance. Even though debate continues as to if and when we might detect a change in temperature from increases in atmospheric trace gases, the impact on plants of the well-defined and continuing increase in just one of those gases, carbon dioxide, is immediate and underappreciated. Plant photosynthesis and physiology are altered by increased carbon dioxide, although the changes vary across species and systems. Crops, for example, now grow faster than they did a few decades ago. Yet the final complex outcome on the functioning, productivity, and composition of natural and agricultural ecosystems is far from known. For instance, photosynthesis is also affected by levels of light-too much can damage the photosynthetic machinery and depress a plant's productivity. Understanding this mechanism of photoinhibitor and its impact in nature has become timely because 0 stratospheric ozone depletion and the likelihood of increased photodamage to plants and marine algae because of increased levels of ultraviolet radiation.⁵

Throughout history, human destiny has been distinctly shaped by our interactions with plants, from the development of agriculture, through the New World voyages spurred by the search for spices, to the Green Revolution. There is no reason to believe that our destiny is now any more separate, even though relatively fewer and fewer people have any practical or intellectual knowledge of plants. if anything, our dependence is tighter, as we have come to rely on only about 20 plant species to provide the bulk of the world's food,⁶ while the global stock of 250,000 land plant species diminishes in numbers and variability.

⁴As additional testament to their underused versatility, algae have important roles in the food industry, as thickeners, stabilizers, and sushi wrappers. Agar and agarose from algae are also staples in science, for growing biological cultures and analyzing biomolecules. DNA fingerprinting, for example, uses agarose as a medium for separating DNA fragments.

⁵ Research on the effects of ultraviolet radiation on marine algae and other organisms has had at least one practical spin-off: the algae were found to produce novel protective compounds, known as mycosporine-like amino acids, in response to increased ultraviolet radiation more stable and protective than the usual sunscreen ingredients, these compounds are now being synthesized for use in sunscreens in Australia and other countries.