Introduction and Historical Background
How has plant classification changed over the years?
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The earliest classifications of plants were based on whether the plant was considered medicinal or was shown to have other uses. De re Rustica by Cato the Censor (234–149 b.c.e.) lists 125 plants and was one of the earliest catalogs of Roman plants. Gaius Plinius Secundus (23–79 c.e.), known as Pliny the Elder, wrote Historia naturalis, which was published in the first century. The book was one of the earliest catalogs of significant plants in the ancient world, describing more than 1,000 plants. Plant classification became more complicated as more and more plants were discovered. One of the earliest plant taxonomists was the Italian botanist Caesalpinus (1519–1603). In 1583 he classified more than 1,500 plants according to various attributes, including leaf formation and the presence of seeds or fruit.
John Ray (1627–1705) was the first botanist to base plant classification on the presence of multiple similarities and features. His Historia Plantarum Generalis, published between 1686 and 1704, was a detailed classification of more than 18,000 plants. The book included a distinction between monocotyledon and dicotyledon flowering plants. The French botanist J.P. de Tournefort (1656–1708) was the first to characterize genus as a taxonomic rank that falls between the ranks of family and species. De Tournefort’s classification system included 9,000 species in 700 genera. The Swedish naturalist Carolus Linnaeus (1707–1778) published Species Plantarum in 1753. It organized plants into 24 classes based on reproductive features. The Linnaean system of binomial nomenclature remains the most widely used system for classifying plants and animals. It is considered an artificial system since it often does not reflect natural relationships.
During the late eighteenth century several natural systems of classification were proposed. The French botanist Antoine Laurent de Jussieu (1686–1758) published Genera Plantarum. The tome Prodromus Systematis Naturalis Regni Vegetabilis was started in 1824 by the Swiss botanist Augustin Pyrame de Candolle (1778–1841) and completed 50 years later. Another Genera Plantarum was published between 1862 and 1883 by the English botanists George Bentham (1800–1884) and Sir Joseph Dalton Hooker (1817–1911).
Charles Darwin’s (1809–1882) ideas on evolution began to influence systems of classification during the late nineteenth century. The first major phylogenetic system of plant classification was proposed around the close of the nineteenth century. Die natürlichen Pflanzenfamilie (The Natural Plant Families), one of the most complete phylogenetic systems of classification and still in use through the twenty-first century, was published between 1887–1915 by the German botanists Adolf Engler (1844–1930) and Karl Prantl (1849–1893). Their system recognizes about 100,000 species of plants, organized by their presumed evolutionary sequence.
Systems of classifications were also developed during the twentieth century. Some works focused on groups of plants, especially flowering plants, rather than all plants. Charles Bessey (1845–1915) was the first American scientist to publish a system of classification in the early twentieth century. Cladistics is one of the newest approaches to classification. It is often defined as a set of concepts and methods for determining cladograms, which portray branching patterns of evolution.