Duke University Alumni Magazine

by Dennis Meredith

Curator Bohs: "If you need to look at the hairs on the corolla of a flower under the microscope, you can look at the real hairs, not just a description of them."
Photo: Chris Hildreth

From Costa Rica to Australia, from Bolivia to China, Duke botanists travel the planet to gather and study strands of life's intricate web.

ynn Bohs can stroll from Costa Rica to Australia in a minute or so, from Bolivia to China in less time, if she walks fast. And the Duke botanist can leap the decades from the 1930s to the 1950s to the 1980s with the twist of a few metal handles. Those handles open the sealed doors of some 700 gray steel cabinets crowding the rooms and halls of Duke's Biological Sciences building, and they contain the extraordinary scientific wealth of the 720,000 plant specimens of the Duke herbarium.

Bohs can open folder after folder, revealing myriad plant species, each displayed on a sheet of heavy, acid-free paper with a label documenting where, when, and how each was collected by generations of botanists who have led worldwide expeditions into forests, jungles, and tundra over the last half-century. A massive trove of flowering plants, ferns, mosses, lichens, and mushrooms, the herbarium comprises one of the leading such collections at any university. Much more than an exercise in botanical bookkeeping, the collection constitutes an ecological treasure. The enduring dividends it returns include scientific insights into the Earth's complex web of plant life. The vast collection also enables Duke students to undertake broad-ranging tours of the world's flora without leaving campus. Although the herbarium has been compared to a library, it offers a far richer scientific resource than any collection of books, says Bohs, who is curator of the herbarium's collection of "vascular plants" --those with stems and leaves.

"These specimens aren't a picture or a drawing of a plant. It's the plant itself," she says. "So, if you need to look at the hairs on the corolla of a flower under the microscope, you can look at the real hairs, not just a description of them. Or, when someone first describes a specimen, even though they think they described everything, I might decide the internal stem structure is important. And with an actual specimen, I can go back and examine that." Similarly, she and her colleagues can apply new technology to old herbarium specimens, yielding scientific insights undreamed of when the initial Duke collectors first traipsed through steamy, uncharted jungles in the 1930s gathering specimens. Certainly, none dreamed that their hard-won finds would be studied using futuristic electron microscopes and DNA sequence analysis to probe plants' evolutionary secrets.

Also, since carefully preserved specimens can last for centuries, Duke's herbarium gives scientists and students alike a first-hand look at botanical history, says Bohs. Sadly, though--given that biologists estimate that 25 percent of all species will go extinct in the next quarter-century--the herbarium may, in fact, become a last resting place for many plants that no longer exist.

The Duke herbarium is used mainly by "systematists," scientists whose aim is to document the Earth's biodiversity and the evolutionary relationships among organisms. Their insights take the form of "phylogenetic trees"--complex diagrams that reveal the hierarchies of species. Such missions are fundamental to inventorying the biodiversity of species, understanding how they evolved, and--critically important--learning to preserve them even as rain forests are burned to make cropland and wetlands filled to make settlements.

Says Jonathan Shaw, curator of the herbarium's 245,000-specimen moss collection: "Herbarium collections are the nuts-and-bolts reservoir, the most important critical resource for understanding patterns and levels of biodiversity. Everything in systematics works from the foundation that the herbarium provides."

Duke's botanists continue to build up that foundation, mounting expeditions, funded mainly by the National Science Foundation, that result in the addition of thousands of specimens each year to the collections. This summer Bohs is traveling to Bolivia in search of ancestors of the tree tomato, in hopes of adding to knowledge of the origins of a useful food crop. Shaw spent a month last summer in the high Arctic gathering mosses, and plans to journey to southern Russia this summer. Among the other botanical expeditioners are Richard Searles, who dives into underwater seaweed forests in the Caribbean; Paul Manos, who prospects for unknown oak species in China and southeastern Asia; Rytas Vilgalys, who gathers fungi in Australia, New Zealand, and New Guinea; botany department chair Donald Stone, who seeks walnut and hickory relatives in Central America; and herbarium pioneer Robert Wilbur, who is completing a twenty-year program to collect and describe some 1,800 fern and flowering plant species from a lush lowland rain forest in Costa Rica.

In their collecting trips, the Duke botanists serve as ambassador/educators, as well as collectors. They often forge research partnerships with local scientists that aid both the host country's knowledge and Duke's research. Manos works with a local Chinese botanist who helps him collect his oak specimens and, in return, Manos performs sophisticated DNA analyses of plants that the Chinese researcher could not do otherwise. Searles is aiding Mexican researchers in cataloguing the rich diversity of seaweeds in the waters of Cozumel, to give a baseline for conservation efforts.

Masses of mosses: a landscape of samples being grown in Duke greenhouses
Photo: Chris Hildreth

Bohs, who works with local botanists in Costa Rica and South America, echoes her colleagues' admiration for the collaborators. "They are just fantastic," she says. "They have very few resources, their salaries are terrible, their facilities are primitive, and yet, they're excellent botanists." Also, as is the custom, the Duke botanists share their finds with their colleagues at other institutions, often collecting multiple specimens to parcel out to other herbaria. And through a loan program traditional in the profession, the Duke herbarium ships thousands of specimens each year around the world for study by fellow scientists.

The Duke botanists downplay the hazards of their field work, which may include snake bites, robberies, accidents on hazardous back-country roads, and even attack by hostile local drug lords. More important to them is the thrill of discovery of a species unknown in an area, or even a totally new species, a not-unusual occurrence even on treks through the "untamed wilderness" of North Carolina. Shaw recalls just such a home-grown surprise on one of his moss-hunting expeditions: "A year ago I was out on a field trip near Highlands, in Macon County, into an area that had been collected many, many times before. I picked up a moss that I didn't recognize, and when I got it back to Duke, it turned out to be a species widespread in the tropics, but previously unknown north of southernmost Mexico."

In fact, says Shaw, North Carolina turns out to be a refuge for many exotic plants. "The southern Appalachians had never been covered by glaciers in the recent past, so there's a tremendous diversity of all sorts of plants and animals because the area's been available to plants and animals for so many more millions of years than further north."

Shaw and his colleagues also find unpleasant surprises on their expeditions, in the form of a steady loss of plant species and their habitat. Says Shaw, "There are many habitats being destroyed in North Carolina alone. There are peat mosses known from a limited number of bogs in the mountains that have disappeared from the state, perhaps becoming even more rare."

Department chair Stone has seen the loss even more dramatically over his nearly four decades of collecting walnut species. "When I first went to Costa Rica in 1961, I put metal tags on the trees that I collected from. And over time, virtually all the tags have disappeared as the trees have been cut down. Where there was once tropical rain forest, there is now a barren field."

The universality of the botanists' depressing encounters has been dramatically confirmed by a worldwide survey of plant species by a coalition of environmental and scientific groups. The survey, released in April, found that one in every eight plant species in the world--and nearly one in three in the U.S.--are under threat of extinction. The finding was especially alarming, the survey report asserts, given that plants undergird most of nature and, in fact, human life. Plants provide the basis for all human foods, much of our clothing and shelter, and most medicines.

Kapoc pods, Pachira aquatica (Bombacaceae)
Photo: Brent Clayton

Once the Duke botanists return from the field with their valued specimens, Stone and his fellow systematists still use the time-honored techniques of botanical description of leaves, flowers, and other structures to help distinguish species. But, increasingly, they depend on analytical machines that their predecessors from the early days would have believed to be nothing less than science fiction. Stone studies the elegantly sculptured pollen grains to distinguish subtly different species of banana, as well as walnut and hickory--but he doesn't just peer into a traditional light microscope. Instead, he freezes the pollen and uses a superfine slicing microtome to make cross-sections of the dust-sized grains, which he scrutinizes using an electron microscope. "The pollen it turns out is a fairly complex unit, with six or seven layers to the wall," he says. "And these layers form in a specific way." Such clues can help Stone fit the plant species into a phylogenetic tree.

Of all the new technologies, DNA analysis --similar to the method used by police laboratories--has become the chief tool of the modern systematist. Rather than catching criminals, the Duke botanists are interested in ferreting out plant lineages and species. The scientists use DNA sequence analyses of the different plants as a sort of "molecular clock" to compare how the plant species have changed and to organize them into phylogenetic trees. Different genes prove useful for different kinds of measurement. To distinguish subtle differences among different populations of a single species, the scientists analyze genes that evolve rapidly over time--like using a stopwatch to time a Kentucky Derby. On a broader scale, to compare more distantly related species, the systematists choose genes that change slowly, like using a calendar to chart the passage of months.

A variety of sunflower, Erigeron glabellus (Asteraceae) The herbarium's oldest specimen, 1862
Photo: Brent Clayton

Shaw uses DNA analyses to map the many species of peat moss, also known as sphagnum mosses. "If we are interested in understanding the evolution of the whole peat moss genus, we'll choose a gene that evolves fairly slowly. Even closely related species will be identical for that gene. That means we can choose a sample that's representative of a species and not have to analyze fifty samples. But in studies in which we're interested in a particular species and how it got such a broad geographic range, then we're sampling individual populations worldwide of the species, and we need a gene that would have changed rapidly over the amount of time that a single species has been in existence."

Some of his DNA studies investigate the fact that many mosses found in the North Carolina mountains are practically identical to those found in eastern Asia, including Japan. The puzzle of how such identical species can exist so widely separated from each other is important to understanding the basic mystery of how species of any animal or plant evolve and persist. "It's a million-dollar question," he says. "Did the mosses move back and forth between Asia and eastern North America? Or does this reflect ancient history, maybe species that are thirty to forty million years old, that somehow remained the same? It's a basic question in biology--why some plants and animals become different over that amount of time and others don't."

From the mangosteen family, Clusia valerii (Clusiaceae)
Photo: Brent Clayton

Shaw's DNA detective work has also turned up instances in which humans might have had a hand, or maybe a foot, in distributing plant species. He's used molecular analysis to sort out the mystery of the "copper mosses," rare organisms that thrive only in far-flung spots where they have encountered the copper-rich soils they need to grow. These disparate regions include the U.S., the Himalayas, the Philippines, South America, and Mexico. Using fast-changing "stopwatch" markers to distinguish these mosses, Shaw and his colleagues discovered striking similarities between plants growing in Nepal and those growing happily in downtown Tokyo, under the drip lines of the copper-roofs of Buddhist temples. The intriguing possibility, says Shaw, is that ancient Buddhists, migrating from western Asia into Japan, may have inadvertently carried hitchhiking moss spores. Thus, he says, analysis of plants can give clues to human history.

As for Rytas Vilgalys, he and his colleagues seek to unearth the mysteries of mushrooms, ambitiously performing DNA comparisons of 800 species to build a many-branched phylogenetic tree. He is also performing cross-breeding experiments to explore the phenomenon of "intersterility," in which different species rarely interbreed, even when growing on the same log. "This species question is one of the oldest in biology. Why isn't there just one species with local variations?" he asks. "Nobody knows how these species maintain their individuality." Vilgalys and other biologists believe that geographical separation may play a key role in species evolution, but the mysteries of species formation remain profound.

Glistening oyster mushrooms (Pleurotus)
Photo: Chris Hildreth

The phylogenetic trees that the Duke systematists build represent more than organizational charts of plant species; they are maps that guide scientific insight into these mysteries of evolution, according to Paul Manos. "Knowing the pattern of evolution, as is gained with phylogenetic trees, is critical to studying the process of evolution. These trees are used to test hypotheses of how organisms adapted and changed. So, it's really become apparent for any systematist that not only are they doing all the leg work for understanding how many species are out there, but they're usually going one step further. They're constructing evolutionary hypotheses."

Manos uses the Duke herbarium's wealth to show students dramatically the incredible richness of life that evolution has produced. "When I teach a course on plant families, I use the live plants to show part of the diversity. But then I also get the herbarium sheets to show just how diverse a plant family is. It's important for students to really learn the entire breadth of plant species as much as possible."

Unfortunately, for both the faculty and the students, Duke's herbarium has fallen far behind, both in space for plants and the computer technology to organize them. The hundreds of herbarium cases lining the biology building's hallways are nightmares for both scientists and fire marshals. The herbarium's record-keeping practices are reminiscent of the mom-and-pop grocery stores of the 1950s, consisting of laboriously handwritten records of specimen loans and, in fact, no overall inventory of the collection. Even as the herbarium runs out of room, thousands of new specimens stream in each year, the sign of an active, growing science. "We're overflowing right now," says Stone, "which means that the collections can't be properly taken care of, nor can they be accessed readily by students and scientists, or shared with the community of scientists."

Thus, Stone and the other botanists have proposed building a modern, efficient Duke Biodiversity Center for Teaching and Research that would give plants, faculty, and students alike a better home. The priceless plant specimens would be preserved in rooms with controlled temperature and humidity, isolated from plant-eating pests. And people would study and learn about the plants in the building's teaching lab, offices, and auditorium. The $6-million investment would also attract federal funding to pay for motorized, mobile "compactor" shelving that telescopes to maximize storage space. Such funding would also support the gargantuan task of creating the first computer database of the collection.

Computer records could greatly enhance the herbarium's use by scientists at Duke and worldwide, says Bohs. "Right now, I can get on my computer and easily access information on specimens from herbaria at other institutions. In fact, I can even ask an herbarium in Costa Rica to pull a specimen and scan it into the computer so I can look at it over the Internet." Adds Stone, "Computerization is a chicken-and-egg situation, in a sense. It makes little sense to computerize the collection now when we can't even maintain it properly and it's scattered throughout the building."

To put it botanically, the Duke systematists believe that the new center will allow cross-fertilization of ideas and knowledge among scientists and students, resulting in a new breed of broad-ranging expert that can tackle the vast problems of preserving nature's biological wealth. "Duke has individual strengths in biodiversity studies, but they are not integrated," says Vilgalys. "We have ecologists, we have systematists, and we have conservation biologists. But we don't have a space for people to get together to exchange ideas about this biodiversity crisis."

The Duke botanists and their fellow biologists are excruciatingly aware that ignorance of Earth's creatures could well spell doom

for many. They live with the frustrating knowledge that science has discovered and catalogued only a puny 15 percent of the 10- to 100-million species of plants and animals estimated to inhabit the planet. Perhaps the most ironic, tragic symptom of our disregard for Earth's web of life, they say, is that we neglect the task of tracing its strands even as we unravel them.


A pressing profession: Herndon, in an office piled high with samples, meticulously prepares specimens for mounting
Photo: Chris Hildreth

I'm not saying I'm an artist," insists Sherri Herndon, who nevertheless artfully arranges the exotic Costa Rican plant just so on the large sheet of heavy herbarium paper--with leaves handsomely fanned out displaying both front and back, flowers and seeds up front. "But you have to have a feel for it," she adds, as she prepares to paste the specimen into place. "I really love it. I really love my job."

No doubt Duke's botanists love having her do it, for Herndon is considered a master of the art and craft of preparing plant specimens after more than three decades as the "heart of the herbarium," the chief preparer of tens of thousands of vascular plant specimens laboriously fetched by the botanists on arduous treks to the ends of the Earth.

Not many people can claim that their work will be appreciated a century from now, but no doubt some twenty-first-century botanist will give thanks for Herndon's meticulous care. "We're almost universally complimented on our herbarium specimens," says Robert Wilbur, who himself has contributed some 70,000 specimens to the herbarium over the decades. "Other botanists borrow our specimens by the thousands every year, and we get letters back saying what superior specimens they are. It's really rewarding. You don't want to cut corners when these specimens are so precious."

Indeed, the initial pasting of plants on paper is only the beginning of the preparation process. Later, heavy parts such as thick stems and seed pods will be fastened by linen strapping and even sewn into place. An envelope will also be fastened to the sheet, just in case pieces should fall off, and to hold extra bits of material for closer study or possible DNA analysis.

Herndon thoroughly documents each specimen, preparing a label that records the most exact location possible where the plant was collected, so botanists can return to the very spot, if necessary. She even includes such details as the colors of the flowers and the date the plant was collected, so scientists will know as much as possible about the point in the plant's life cycle when it was collected.

The paste-up completed, she covers the herbarium sheet with wax paper and stacks it between layers of foam rubber to dry, creating a growing pile representing her day's work. That's one more specimen completed. But what does Herndon think about the 40,000 others still waiting to be mounted, sitting in great stacks of cardboard boxes in a room down the hall? And is she haunted by the backlog that grows by thousands every year?

"I call it job security," she says, laughing. Then she slides another swatch of dried plant gently from its resting place between sheets of newspaper, pondering how to arrange it so the specimen will yield the keenest scientific insight for future scientists and students.

Share your comments

Have an account?

Sign in to comment

No Account?

Email the editor