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ANATOMY OF A ROSE -- EXPLORING THE SECRET LIFE OF FLOWERS |
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ELEVEN: The Tower of Babel and the Tree of Life BOTANISTS CAN SOUND PLEASANTLY archaic or irritatingly pompous. They may know the common name of a flower, a blackfoot daisy, but they say Asteraceae instead. They love the jangle of Latin and vie for the prize of most fluent. Is that a Melampodium leucanthum? A Chrysanthemum leucanthemum? A Monoptilon bellioides? A Bellis perennis? No, not an Eregeron divergens? The adults talk. The children are excluded. "It's a daisy," the layperson mutters under her breath. In traditional taxonomy, the daisy belongs in the kingdom Plantae, in the division Angiospermophyta, in the class Dicotyledoneae, in the order Asterales and in the family Asteraceae, in which there are over one thousand genera. These genera contain some nineteen thousand species. Each grouping (kingdom, division, class) is a taxon, the plural of which is taxa. Taxonomists are people who group things together. Taxonomists belong in the kingdom Animalia, in the phylum Chordata, in the class Vertebrata, in the order Primata, in the family Homonoidea, in the genus Homo, in which there remains only one living species, sapiens. The taxonomist scolds the layperson: There are too many daisies in the world. We need to be more specific. For that matter, there are too many bluebells, the common name for various species in different genera: Wahlenbergia saxicola in New Zealand, Phacelia whitlavia in the United States, Clitoria ternatea in West Africa, Campanula rotundifolia in Scotland, and Endymonion non-scriptus in England. In England alone, there are ten different cuckooflowers, all plants that blossom early when the cuckoo sings. There are too many cuckoo-flowers and too many silly common names, like touch-me-not or bloody cranesbill or open-arse or jack-in-the-pulpit or firewheel or scarlet bugler or witch hazel or lady's slipper or figswort or beardstongue or snakebroom. The adults are trying to have a serious conversation, and the adults require a serious language. *** THE FIRST KNOWN WRITTEN classification of plants was in Latin in the fourth century B.C. Almost two thousand years later, an English botanist produced the second major classification, also in Latin. In the eighteenth century, one scientist confessed that when speaking to his father as a boy, he was only allowed to speak in Latin. In this way, he learned that tongue before his native Swedish.
Oxeye Daisy "Help, Father! I'm drowning!" "Filius, filius, lingua latina dicte!" Parenting like this involves a certain distance, some cold calculations, perhaps a rather controlling personality. A similar style might have produced someone like Carl Linnaeus, born in 1707, also in Sweden. Linnaeus's father was a clergyman and an avid botanist, as were his uncle and grandfather. (His great-grandmother had also been a botanist, which caused her to be burned as a witch.) Linnaeus grew up to be a proud, vain, insecure man whose genius lay in organizing plants, which he grouped into twenty-four classes based on their reproductive parts. "God creates," Linnaeus said, "Linnaeus arranges." Arrogance may be necessary for cataloging the world. In the promotion of his work, Linnaeus also found it helpful to refer to himself in the third person. People took him seriously. Artificial, and sometimes strange, his system was still more convenient and more comprehensive than any of its time. In a matter of years, it became the standard. Importantly, Linnaeus gave a binomial, or two-part name, to each species. This is the method we still use. The first part, or capitalized word, is the genus, for example, Mentha for mint or Vitis for grapes. The second, uncapitalized word is often descriptive: Mentha peperita for peppermint or Vitis vinifera for a common wine grape. Today scientists follow a set of rules, the International Code of Botanical Nomenclature (the Botanical Code), whenever they discover a new species. The species is first assigned its place in the ranking of kingdom, division, class, order, family, and genus. The discoverer then uses the binomial system to choose a name. A description of the plant in what we call Botanical Latin and in the botanist's own language is submitted to the appropriate journal, where editors and others determine if the species is really new and the name really unique. Botanical Latin has simplified the ancient grammar, added words, and changed the meaning of words. It would sound Greek to a classical Latin scholar or to an early Roman. Still, as one linguist notes, a living dog is better than a dead lion. Botanical Latin is a living dog. Eregeron divergens. Monoptilon bellioides. The words that first clank and clatter in your mouth will soon gather smoothness, like rocks being smoothed by the water of a stream, tumbling, turning, weighted with history, suddenly light. Melampodium leucanthum. Bellis perennis. You, too, can join the conversation. You, too, will feel special. *** CARL LINNAEUS CLASSIFIED FLOWERS a hundred years before the publication of the theory of evolution. Linnaeus used physical features to group plants. Most of his classifications were obsolete by the nineteenth century. What remains is his binomial naming system and the hierarchy of ranks. Modern taxonomists try to group plants based on their descent, in terms of how and when they evolved through time. Down the line, in each rank, organisms share more and more similar features until, at the level of the species, they share enough reproductive features to breed together and produce a fertile generation. Down the line, in each rank, organisms share a closer and closer evolutionary relationship. Taxonomists agree that their groupings should reflect evolution. They do not all agree on which features of a plant are primitive and which are more recent, on which are important for designating a rank and which are not. For this reason, biologists use a number of different taxonomic systems, which reflect the different personalities of their taxonomists. For example, plants that produce legumes or beans as fruit can be divided into three groups, based on their different flower forms. A mimosa flower is circular, or radially symmetrical. A common pea flower is bilaterally symmetrical with five petals; the middle petal is larger, distinct, and protrudes from the bud. A honey locust flower is also bilateral with five petals; the middle petal is neither large nor distinct nor exterior to the bud. If you think these flower shapes are important, you will divide these three groups into three families. People will call you a splitter. If you think these shapes are not important, if you believe that the fruit or legume is what matters, you will lump all these plants into one family, with three subfamilies. People will call you a lumper. You may use another approach to develop your taxonomy: cladistics. First you find a specific aspect of a plant that you can theorize as primitive or derived. The red flower of a rose and of a hedgehog cactus are produced by two chemically different pigments. Which pigment came first and which came from the other? Different cladograms, or pictures, will show different patterns or branches of evolution. With a complex question involving many factors, there may be hundreds or thousands or millions of possibilities. Computers do the math, helping you guess which alternative is most likely. New tools are available to all taxonomists. We can now look into the DNA of a plant and gauge when, how, and from what it evolved. We examine cells. We examine genes. We examine chromosomes. We draw back from the microscope with some dismay. Many of our current classifications are wrong. Every day, there is more bad news: The lotus is not related to the water lily. Lotuses belong with sycamores. One little-white-flowering mustard, Arabidopsis thaliana, is commonly used by laboratory scientists. The first plant to have its entire genome sequenced, it has been used in hundreds of studies and reports. We know an extraordinary amount about this plant. Unfortunately, when a botanist studied the twenty-five other species in its genus, twenty were found to have no evolutionary relationship. The plant would have to be renamed. Around the world, plant geneticists were appalled. The sheer volume of new information about plants is becoming harder and harder to fit into the traditional system of ranks -- kingdoms and phyla and classes and families and genera and species. Students used to memorize these ranks by reciting mnemonic phrases: King Philip Came Only For Gold and Silver. Then taxonomists began to add superorders, subfamilies, tribes, cohorts, phalanxes, subcohorts, and infraphalanxes, all of which require phrases too long to be mnemonic. In the current system, new discoveries can have a domino effect. Changing the name of a plant's lineage may mean changing the names of any number of other plants. Changes in the Botanical Code can be complex and painful. Simply naming a plant with the Botanical Code can be complex and painful. Some biologists want a new system. They want to abandon the contorted, inconsistent grouping of organisms into ranks like kingdom, phylum, and class. Instead, a plant would be given a single proper name, which would indicate its evolutionary path. That name would retain the Linnaean sense of hierarchy, one group "nested" inside a larger group. Humans might be called Sapiens Homo Homidae Primata Mammalia Vertebra Metazoa Eucaryota or, for short, Sapiens Homo. If we learn something new (if we really do have extraterrestrial ancestors), changing that name will be easy. No one would care about King Philip anymore. "It's the greatest thing since sliced bread," says one botanist. "It's moronic," says a colleague. "It's tempting," says a third. It's another problem in communication. *** WE WANT TO KNOW the daisy by naming it. Then the whole thing snowballs. We want to know the names of the daisy's relatives and the names of the plants related to those plants and the names of the plants related to those plants, and we realize that we want to name the whole world. The daisy is a tiny part of what botanists call the tree of life. We want to know the tree of life. It's more than finding a common language, more than having a conversation. It's about how all the names begin to connect and interact, how the words form into something larger, like the cellular growth of a plant itself, budding into branches and leaves, an embrace of everything alive on this earth. The tree of life. Commonly, we draw a picture in which the base of the tree starts with simple, single cells. These cells, or prokaryotes, have few internal structures. Some are adapted to live in difficult climates, like very hot pools or the harsh environment of a young planet. Above the prokaryotes, we have cells called eukaryotes, which are more complex, with a center or nucleus and other internal structures. Both these single-celled life forms make up, by far, the largest and most unexplored part of the tree. There are millions and millions of species here that we have not yet discovered or even bothered to discover. This enormous "trunk" is often divided into two kingdoms: Monera and Protista. Higher now, toward the top, single complex cells combine into multicellular eukaryotes. This is what we call the crown of the tree. We used to divide this crown into three branches or kingdoms: Plantae, Fungi, and Animalia. Lately, research has been playing among these branches like a great wind. The single branch Plantae is really three separate groups, three lineages that evolved from three different one-celled organisms. Green plants are green algae and all land plants. Red plants are red algae. Brown plants are brown algae, diatoms, and organisms that look like plants but do not use photosynthesis. Fungi, including yeasts and mushrooms, are a fourth branch. A mushroom may sit around and grow like a daisy. But mushrooms and other fungi are evolutionarily more related to animals than to plants. Animals (drumroll, please) are a fifth branch. From a medical standpoint, our evolutionary closeness to fungi means that fungal infections are difficult to treat because whatever is harmful to the infection is often also harmful to us. Like kissing cousins, we have too much in common. Knowing who goes where and who is related to whom on the tree of life is useful. Our response to a disease changes if we know it is bacterial and not fungal. In other cases, if a plant is helpful to us in some way, its relatives may also be helpful. When researchers found that the Pacific yew tree produced taxol, a cancer-fighting drug, the yew tree soon became endangered through overharvesting. Quickly we looked for related species that also produce taxol. We even found a species of fungus, living on the yew tree, that makes taxol as well. Yew tree, fungus, and researcher: We are more closely related than we like to think. We huddle together on our part of the tree, surrounded by bacteria, outnumbered by microbes. *** IN THE TREE OF LIFE, the human twig is small. Our kingdom, Animalia, is minuscule. Even so, we have a singular power. We're the mouse that roared. We roar out names. We dream about names. We praise those gods who gave us the names of all the animals and all the plants and all the living things on earth. We know that naming is magical. We know that naming is ownership. A rose by any other name would smell as sweet. But that's just the opinion of one man. Maybe it would not smell as sweet. Maybe it would smell differently. Maybe a name makes all the difference in the world. It's a daisy. It's pretty. Its center is the color of egg yolk. It has milky white petals. We pick those petals, one by one, and we whisper, "He loves me. He loves me not." We make a wreath to put on our heads. We want to name the daisy. It's Eregeron divergens. No, it's Bellis perennis. No, it's Chrysanthemum leucanthemum. With some ceremony, we put the daisy in its rightful place on the tree of life.
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