Thehistory of plant systematics—thebiological classification ofplants—stretches from the work of ancient Greek to modernevolutionary biologists. As a field of science, plant systematics came into being only slowly, early plant lore usually being treated as part of the study of medicine. Later, classification and description was driven bynatural history andnatural theology. Until the advent ofthe theory of evolution, nearly all classification was based on thescala naturae. The professionalization of botany in the 18th and 19th century marked a shift toward more holistic classification methods, eventually based on evolutionary relationships.
Theperipatetic philosopherTheophrastus (372–287 BC), as a student ofAristotle inAncient Greece, wroteHistoria Plantarum, the earliest surviving treatise on plants, where he listed the names of over 500 plant species.[1] He did not articulate a formal classification scheme, but relied on the common groupings offolk taxonomy combined with growth form: tree shrub; undershrub; or herb.[citation needed]
TheDe Materia Medica ofDioscorides was an important early compendium of plant descriptions (over five hundred), classifying plants chiefly by their medicinal effects.
TheByzantine emperorConstantine VII sent a copy ofDioscorides' pharmacopeia to theUmayyad CaliphAbd al-Rahman III who ruledCórdoba in the 9th century, and also sent a monk named Nicolas to translate the book into Arabic.[2] It was in use from its publication in the 1st century until the 16th century, making it one of the majorherbals throughout the Middle Ages.[3][4] Thetaxonomy criteria of medieval texts is different from what is used today. Plants with similar external appearance were usually grouped under the same species name, though in modern taxonomy they are considered different.[5]
Abū l-Khayr's botanical work[6] is the most completeAndalusi botanical text known to modern scholars. It is noted for its detailed descriptions ofplant morphology andphenology.[5]
In the 16th century, works byOtto Brunfels,Hieronymus Bock, andLeonhart Fuchs helped to revive interest in natural history based on first-hand observation; Bock in particular included environmental and life cycle information in his descriptions. With the influx of exotic species in theAge of Exploration, the number of known species expanded rapidly, but most authors were far more interested in the medicinal properties of individual plants than an overarching classification system. Later influential Renaissance books include those ofCaspar Bauhin andAndrea Cesalpino. Bauhin described over 6000 plants, which he arranged into 12 books and 72 sections based on a wide range of common characteristics. Cesalpino based his system on the structure of the organs of fructification, using the Aristotelian technique oflogical division.[3]
In the late 17th century, the most influential classification schemes were those of English botanist and natural theologianJohn Ray and French botanistJoseph Pitton de Tournefort. Ray, who listed over 18,000 plant species in his works, is credited with establishing themonocot/dicot division and some of his groups—mustards,mints,legumes andgrasses—stand today (though under modern family names). Tournefort used an artificial system based on logical division which was widely adopted in France and elsewhere in Europe up until Linnaeus.[3]
The book that had an enormous accelerating effect on the science of plant systematics wasSpecies Plantarum (1753) byLinnaeus. It presented a complete list of the plant species then known to Europe,[1] ordered for the purpose of easy identification using the number and arrangement of the male and female sexual organs of the plants. Of the groups in this book, the highest rank that continues to be used today is thegenus. The consistent use ofbinomial nomenclature along with a complete listing of all plants provided a huge stimulus for the field.[citation needed]
Although meticulous, the classification of Linnaeus served merely as an identification manual; it was based onphenetics and did not regard evolutionary relationships among species.[1] It assumed that plant species were given by God and that what remained for humans was to recognise them and use them (a Christian reformulation of thescala naturae orGreat Chain of Being). Linnaeus was quite aware that the arrangement of species in theSpecies Plantarum was not a natural system, i.e. did not express relationships. However he did present some ideas of plant relationships elsewhere.
Significant contributions to plant classification came fromde Jussieu (inspired by the work ofMichel Adanson) in 1789 and the early nineteenth century saw the start of work by de Candolle, culminating in theProdromus.[citation needed]
A major influence on plant systematics was the theory ofevolution (Charles Darwin publishedOrigin of Species in 1859), resulting in the aim to group plants by theirphylogenetic relationships. To this was added the interest inplant anatomy, aided by the use of thelight microscope and the rise of chemistry, allowing the analysis ofsecondary metabolites.
Currently, the strict use ofepithets in botany, although regulated by international codes, is considered unpractical and outdated. The very notion ofspecies, the fundamental classification unit, is often up to subjective intuition and thus can not be well defined. As a result, estimate of the total number of existing "species" (ranging from 2 million to 100 million) becomes a matter of preference.[1]
While scientists have agreed for some time that a functional and objective classification system must reflect actual evolutionary processes and genetic relationships, the technological means for creating such a system did not exist until recently. In the 1990s DNA technology saw immense progress, resulting in unprecedented accumulation ofDNA sequence data from various genes present in compartments of plant cells. In 1998 a ground-breaking classification of the angiosperms (theAPG system) consolidatedmolecular phylogenetics (and especiallycladistics orphylogenetic systematics) as the best available method. For the first time relatedness could be measured in real terms, namely similarity of the molecules comprising the genetic code.[1]
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