Taxonomy, History Of | Research & Encyclopedia Articles

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Taxonomy Summary

Taxonomy, History Of

The origin of plant taxonomy goes back centuries, and there are thought-provoking parallels between folk classifications and those produced in more recent times. The Swedish botanist Carolus Linnaeus (1707-1778) provided the first widely used framework, the basis of our current classification. He placed all plants in a genus and species, giving each a binomial (such as Taraxacum officinale for the dandelion), allowing botanists worldwide to communicate.

Linnaeus was not very successful in recognizing larger groupings of plants, but in 1786 Antoine-Laurent de Jussieu put all genera in families. Jussieu believed that nature could be represented as a single, continuous series of relationships, and he made his families (and genera) of convenient sizes. There was much debate during the ensuing century and a half as to whether all characters should be used in classification or only in the most important ones. The issue was never resolved, but in practice the human mind cannot compute relationships using all characters. Another issue was less contentious: It had been realized that prominent characters used for the identification of plants (in keys) might be different from the most fundamental ones used in deciding on the same plant's relationships.

The Nineteenth Century

The late eighteenth and the nineteenth centuries saw many new developments in the area of plant taxonomy. Voyages of discovery and colonization yielded a stream of unknown plants needing names. Plants of economic importance like quinine, breadfruit, rubber, and tea were moved to colonies where they could best be exploited. Herbaria, collections of flattened and dried plants attached to paper, were developed. By the middle of the nineteenth century most large herbaria such as those at Washington, D.C., Kew (London), and Paris were owned by the state or, less frequently, universities. Systematic work was largely based on the dried plants there, with botanical gardens or field studies being of less importance. This practice persisted through much of the twentieth century.

Darwin's ideas on evolution, published in 1859, had little effect on the practice of taxonomy, although many workers used the ideas to explain the classifications they produced—using techniques very similar to those of Jussieu. Systematists like Asa Gray were among Darwin's staunchest supporters. Darwin himself was very interested in genealogies, ancestor-descendant sequences. Most botanists thought that without fossils such genealogies could not be recognized, but nonetheless when they talked about relationships it was most often in terms of living group A giving rise to living group B—just as if they were talking about genealogies.

Along with professional taxonomists, there was a flourishing group of amateurs. Botany was particularly popular among women. In the later nineteenthcentury, first in Germany and later in the United States, reaction against classificatory botany set in. Physiology, anatomy, ecology, and the study of lower plants were thought to be more exciting, particularly among those who worked at universities. Charles Bessey was a forceful proponent of this "new Botany" in the United States, and although he was not particularly against taxonomy, the popularity of the new approach led to a decline in the status of taxonomic botany and of taxonomists. In the sometimes bitter arguments, taxonomic botany was often portrayed as an old-fashioned subject practiced by women and children and of no scientific interest.

In the 1930s emphasis came to be placed on the study of living plants both in the wild and the greenhouse, particularly in the area of species and speciation. G. Ledyard Stebbins, one of the most influential botanists of his time, was a founder, along with Ernst Mayr, Gaylord Simpson, and others, of the "evolutionary synthesis," an integration of evolutionary theory, systematics, and morphology. However, taxonomists working in herbaria— where most taxonomic work was still carried out—were little affected by such developments.

Since the late nineteenth century, new disciplines such as anatomy, cytology, and plant chemistry had been promoted as likely to solve the difficult problem of understanding the limits and relationships of groups like genera and families. Progress, however, was painfully slow. In the latter part of the twentieth century, a system of relationships that built on those of earlier works was proposed by Arthur Cronquist.

Phenetics and Cladistics

However, changes were afoot. In the 1960s phenetics, or numerical taxonomy, was very popular. By looking at many characters and using early computers to analyze the data, botanists hoped to produce classifications of maximum usefulness, stability, and objectivity. Such botanists were less interested in evolutionary relationships, and problems became evident both in the goals of phenetics and in some analytical techniques. Nevertheless, many of their techniques remain useful, particularly when working at the level of species. In the late 1970s the cladistics approach of Willi Hennig became widely known, and this led to the development of new ways of producing treelike diagrams depicting hypothesized phylogenetic relationships. In such phylogenies, genera and species were not linked directly but by way of their common ancestors. After much debate, Hennig's principles, somewhat modified, have been accepted by most botanists, allowing taxonomists to justify their work much more clearly.

In the 1990s the advent of molecular techniques, combined with the practice of phylogenetic analysis and the use of computers, led to a rapid improvement in our understanding of relationships among the main groupings of plants. This has become perhaps the most common kind of systematic work in universities and is notable for being highly collaborative, contrasting with the individuality of classic taxonomic work. Studies on biogeography, evolution, and diversification have been greatly facilitated as a result. However, morphological studies have tended to stagnate, and there has been relatively little emphasis on studies at the species level. Furthermore, interest in conservation and biodiversity has made it clear how little we understand about most species that have been described, how many species—particularly in groups like fungi—remain to be described, and howfew systematists remain engaged in this kind of work.