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A thoughtful person, Sullivan measures her words carefully, just as she has measured thousands of plant parts for the herbarium, a library of dried plant specimens. She is a leading authority on the genus Physalis, which includes roadside weeds called ground cherries as well as the Mexican husked tomato called a tomatillo. Details are her stock in trade.

Sullivan has used more than 40 characteristics to redefine some of the species in Physalis. She has examined thousands of specimens, measuring the pedicels (stalks that support flowers) and describing the maculations (spots) on their petals. She has analyzed the chemical composition of these plants, hybridized them, observed bees' behavior around them and scanned their pollen with an electron microscope. Among the characteristics she studied, her favorite may be the "lovely little branching hairs" on the undersides of the leaves in some species. She and a German colleague did extensive research on the morphology and development of these tiny hairs, which look like crisscrossing glass filaments under a dissecting microscope.

Advances in molecular biology have taken the minutiae of taxonomic research to even more minute levels, and some long-standing taxonomical problems are being resolved as a result. Working in collaboration with plant biologist Chris Neefus, molecular biologist Anita Klein, and graduate student Troy Bray, Art Mathieson has used molecular methods to study seaweeds in the genus Porphyra, which includes the nori used in sushi. DNA sequencing has helped the researchers discern the differences among five species that were previously considered one species.

While taxonomic work can look like counting angels on the head of a pin--literally splitting hairs, or even DNA--the practical implications can be profound. Porphyra, whether destined for sushi or pigments used in scientific research, is being cultivated around the world. Failure to distinguish among these species when

Tiny gland-tipped hairs, magnified 30x, on the stems of clammy ground cherry, Physalis heterophylla.

propagating plants for aquaculture could lead to the introduction of an alien species into some areas. When Caulerpa taxifolia, a cultivated aquarium plant, escaped from a museum in Monaco in 1984, few people recognized the danger it posed. The plant, dubbed the killer algae, has since spread at the expense of native flora and fauna. Today it carpets 60,000 acres of the Mediterranean Ocean floor and is considered beyond control.

Slicing and dicing DNA

Ironically, advances in molecular biology appear to be simultaneously helping and hurting the field of botanical taxonomy. In addition to elucidating differences among closely related species, molecular research has increasingly enabled taxonomists to make evolutionary relationships the basis of their classification systems. "If your classification scheme tells you something about evolutionary relatedness," Sullivan explains, "you can make predictions about how something will grow, what its chemical makeup will be and whether its use will be positive or negative." Since the 1970s, for example, researchers have been looking for ways of producing the cancer drug Taxol without destroying thousands of the Pacific yew trees in which it was first discovered. Scientists had only to look for closely related species within the same genus. A number of cultivated species of yews produce the necessary chemical in their needles, which unlike the bark of 100-year-old trees, is an easily renewable resource.

Unfortunately the cutting-edge work of slicing and dicing DNA makes traditional taxonomic pursuits like slogging through a bog or measuring pedicels in a herbarium seem antiquated. Money for molecular equipment may come at the expense of important resources like the herbarium, and the push to produce scientists with molecular training is reducing the number of scientists skilled in fieldwork. Grant money also comes more easily to DNA-related research.

"Every time a new technology is introduced there's a bandwagon factor," explains Sullivan. "But there probably isn't one technique that's going to give us The Truth." She believes systematics research should combine up-to-the-minute techniques with knowledge of plants in their natural environment, plus an understanding of earlier attempts at classification.

Molecular work is "only as good as the taxonomy that goes with it," insists Mathieson, who has seen genetic research in a major database applied not only to the wrong species, but even the wrong genus. "There are fewer and fewer people doing active fieldwork," he laments. Although the students he works with in marine ecology learn molecular methods in the lab, he makes sure that they also get plenty of experience in the field--and the herbarium.

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