Cultivated plant taxonomy

Sumerian harvester's sickle made from baked clay and dated to about 3000 BCE.

William T. Stearn (1911–2001), taxonomic botanist, classical scholar and author of the book Botanical Latin has commented that "cultivated plants [cultigens] are mankind's most vital and precious heritage from remote antiquity".[21] Cultigens of our most common economic plants probably date back to the first settled communities of the Neolithic Revolution 10,000 to 12,000 years ago although their exact time and place of true origin will probably remain a mystery.[22] In the Western world among the first cultigens would have been selections of the cereals wheat and barley that arose in the early settlements of the Fertile Crescent (the fertile river valleys of the Nile, Tigris and Euphrates) in the Western Mediterranean. Food plant selections would also have been made in the ten or so other centres of settlement that occurred around the world at this time.[23] Confining crops to local areas gave rise to landraces (selections that are highly adapted to local conditions) although these are now largely replaced by modern cultivars. Cuttings are an extremely effective way of perpetuating desirable characters, especially of woody plants like grapes, figs and olives so it is not surprising that these are among the first known plant selections perpetuated in cultivation in the West.[24] Migrating people would take their plant seeds and cuttings with them; there is evidence of early Fertile Crescent cereal cultigens being transferred from Western Asia to surrounding lands.[25]

Aristotle (384–322 BCE)

As early as the 5th century BCE the Greek philosopher Hippo expressed the opinion that cultigens (as we call them now) were produced from wild plants as the result of the care bestowed on them by man, a revolutionary view at a time when they were regarded as the special creation and gift of the gods.[26] In devising ways of classifying organisms the philosopher Aristotle (384–322 BCE) established the important idea of a fundamentum divisionis — the principle that groups can be progressively subdivided. This has been assumed in biological classification ever since and is congruent with the relatively recent idea of evolution as descent with modification. All biological classification follows this principle of groups within groups, known as a nested hierarchy, but this form of classification does not necessarily presuppose evolution.[27]

Theophrastus (371–286 BCE)

The earliest scientific (rather than utilitarian) approach to plants is attributed to Aristotle's student Theophrastus (371–286 BCE), known as the "father of botany".[28] In his Enquiry into Plants Theophrastus described 480 kinds of plant, dividing the plant kingdom into trees, shrubs, undershrubs and herbs with further subdivision into wild and cultivated, flowering and non-flowering, deciduous or evergreen.[29]

The utilitarian approach, classifying plants according to their medicinal properties, is exemplified by the work of Roman nobleman, scientist and historian, Pliny the Elder (29–79 CE) author of Natural History.[30] "Cultivars" listed here are named after people, places or special plant characteristics. Most notable is the work of Dioscorides (ca.40–ca.90 CE) a Greek doctor who worked with the Roman army. His five-volume Materia Medica[31] was a forerunner of the herbal which led to the modern pharmacopoeia. This work was endlessly plagiarised by later herbals including those printed between about 1470 and 1670 CE: it listed 600 to 1000 different kinds of plants including the cultigens Gallica, Centifolia, the rose of uncertain origin known as Alba and other rose cultivars grown by the Romans.

Pliny the Elder (29–79 CE)

The first record of a named cultigen occurs in De Agri Cultura.[24][32] written about 160 BCE by Roman statesman Cato the Elder (234–149 BCE) in a list that includes 120 kinds (cultivars) of figs, grapes, apples and olives.[24] The names are presented in a way that implies that they would have been familiar to fellow Romans. The "cultivar" names were mostly of one word and denoted the provenance of the cultivar (the geographical origin of the place where the plant selections were made).[33] Writers up to the 15th century added little to this early work. In the Middle Ages the book of hours, early herbals, illuminated manuscripts and economic records indicate that plants grown by the Romans found their way into monastery gardens. For example, in 827 CE the following herbs were mentioned in the poem Hortulus by Walafrid Strabo as growing in the monastery garden of St Gallen in Switzerland: sage, rue, southernwood, wormwood, horehound, fennel, German iris, lovage, chervil, Madonna lily, opium poppy, clary, mint, betony, agrimony, catmint, radish, gallica rose, bottle gourd and melon.[34] It seems likely that aromatic and culinary herbs were quite widespread and similar lists of plants occur in records of plants grown in Villa gardens at the time of Charlemagne (742–814 CE).[33]

Caspar Bauhin (1550–1624)

The revival of learning during the Renaissance reinvigorated the study of plants and their classification. From about 1400 CE European expansion established Latin as the common language of scholars and it was adopted for biological nomenclature. Then, from about 1500 CE, the publication of herbals (books often illustrated with woodcuts describing the appearance, medicinal properties, and other characteristics of plants used in herbal medicine) extended the formal documentation of plants and by the late 16th century the number of different plant kinds described in Europe had risen to about 4,000. In 1623 Gaspard Bauhin published his Pinax theatre botanici[35] an attempt at a comprehensive compilation of all plants known at that time: it included about 6000 kinds.[36] The combined works of a German physician and botanist Valerius Cordus (1515–1544 CE) which were published in 1562 included many named "cultivars" including 30 apples and 49 pears, presumably local German selections.[33] English herbalist John Parkinson's Paradisi in Sole ... (1629) lists 57 apple "cultivars", 62 pears, 61 plums, 35 cherries and 22 peaches.[37]

With increasing trade in economic and medicinal plants the need for a more comprehensive classification system increased. Up to about 1650 CE plants had been grouped either alphabetically or according to utilitarian folk taxonomy – by their medicinal uses or whether they were trees, shrubs or herbs. Between 1650 and 1700 CE there was a move from the utilitarian back to a scientific natural classification based on the characters of the plants themselves.[38]

In 1700 French botanist J.P. de Tournefort although still using the broad groupings of "trees" and "herbs" for flowering plants, began to use flower characteristics as distinguishing features and, most importantly, provided a clear definition of the genus as a basic unit of classification.[39] In Institutiones Rei Herbariae he listed about 10,000 different plants, which he called species, organised into 698 genera with illustrations.[40] The establishment of this precursor of scientific classification vastly improved the organisation of plant variation into approximately equivalent groups or ranks and many of his genera were later taken up by Carl Linnaeus.[41] There was still at this time no common agreement on the way to present plant names so they ranged in length from one word to lengthy descriptive sentences. As the number of recorded plants increased this naming system became more unwieldy.

In England the tradition of documenting garden plants was established long before Linnaeus' Species Plantarum starting with the herbals, but the most prominent early chronicler was Philip Miller (1691–1771) who was a master gardener in charge of the Chelsea Physic Garden in London from 1722 to 1770. New plants were coming into Western Europe from southern Europe and the overseas colonies of the Dutch, British and French. These new plants came largely to the botanic gardens of Amsterdam, Leiden, Chelsea and Paris and they needed recording. In 1724 Miller produced a two-volume compendium of garden plants called The Gardeners and Florists Dictionary or a complete System of Horticulture. The first edition was in 1724, subsequently revised and enlarged until the last and 8th edition in 1768 by which time he had adopted Linnaean binomials.[42] For a while this publication was taken as the starting point for "horticultural" nomenclature equivalent to Linnaeus' Species Plantarum which is now taken as the starting point for botanical nomenclature in general. Miller's Dictionary was the first of many English horticultural compendia whose history has been traced by William Stearn.[43]

Carl Linnaeus (1707–1778) who established the binomial system of plant nomenclature.

In the early 18th century colonial expansion and exploration created a demand for the description of thousands of new organisms. This highlighted difficulties in communication about plants, the replication of their descriptions, and the importance of an agreed way of presenting, publishing and applying their names.

It was the Swedish botanist Carl Linnaeus who finally put order into this situation as he attempted to name all the known organisms of his day.[44] In 1735 his Systema Naturae,[45] which included animals (the tenth edition became the starting point for zoological nomenclature) was followed by Critica Botanica in 1737, and Philosophia Botanica in 1751. But it was his most comprehensive work on plants, the 1753 publication Species Plantarum[46] that formalised the name of a genus with a single epithet to form the name of a species as two words, the binomial thus making secure the biological system of binomial nomenclature. In these works Linnaeus used a third name as a variety within a species. These varieties included both wild and horticultural variants. The horticultural varieties were still written in Latin and some have persisted to this day.

Linnaeus had very definite and uncomplimentary views about cultigens, regarding them as inferior plants for the amusement of those people he disparagingly called anthophiles (flower-lovers); these were plants not deserving the attention of serious botanists. His views revealed both his prejudice, his stance on special creation, and his recognition of the difficulties entailed in cultivated plant taxonomy:

"anthophiles … practice a floral science all their own, grasped only by their devotees; no botanist in his senses will enlist in their camp."[47]

"All the species recognized by Botanists came forth from the Almighty Creator's hand, and the number now and always will be exactly the same, while every day new and different florist's species arise from the true species recognized by botanists, and when they have arisen they eventually revert to their original forms. Accordingly to the former have been assigned by Nature fixed limits, beyond which they cannot go: while the latter display without end the infinite sport of Nature."[48]

"... botany has been overborne by the system of varieties for long enough … few, if any, agree as to what constitutes a species, or what a variety; … I wish the system of varieties were entirely excluded from Botany and turned over entirely to the Anthophiles, since it causes nothing but ambiguities, errors, dead weight and vanity …"[49]

Linnaeus's Species Plantarum of 1753, his catalogue of all the world's plants known to European science.

The natural distribution of plants across the world has determined when and where cultigens have been produced. The botanical and horticultural collection of economically important plants, including ornamentals, was based in Europe. Although economic herbs and spices had a long history in trade, and there are good records of cultivar distribution by the Romans, European botanical and horticultural exploration rapidly increased in the 19th century with the colonial expansion taking place at the time. New plants were brought back to Europe while, at the same time, valuable economic plants, including those from the tropics, were distributed among the colonies. This plant trade has provided the common global heritage of economic and ornamental cultigens that we use today and which formed the stock for modern plant selection, breeding, and genetic engineering. The plant exchange that occurred as a result of European trade can be divided into several phases:[50]

• to 1560 mostly within Europe
• 1560–1620 Near East (esp. bulbous plants from Turkey – "tulipomania")
• 1620–1686 Canada and Virginia herbaceous plants
• 1687–1772 Cape of South Africa
• 1687–1772 North American trees and shrubs
• 1772–1820 Australia, Tasmania, New Zealand
• 1820–1900 Tropical glasshouse plants; hardy Japanese plants
• 1900–1930 West China
• 1930 Intensive breeding and selection programs

As the community of people dealing with the cultigens of commerce grew so, once again, the divergence between taxonomy serving scientific purposes and utilitarian taxonomy meeting human needs re-emerged. In 1865 German botanist Karl Koch, who became General Secretary of the Berlin Horticultural Society, expressed resentment at the continued use of Latin for cultigen names. Many proposals to deal with this were made, perhaps the most prominent being the Lois de la nomenclature botanique submitted in 1867 to the fourth Horticultural and Botanical Congress by Swiss botanist Alphonse de Candolle who, in Article 40 stated:

"Seedlings, half-breeds (métis) of unknown origin or sports should receive from horticulturists fancy names (noms de fantaisie) in common language, as distinct as possible from the Latin names of species or varieties."[51]

Outstanding American cultivated plant taxonomist Liberty Hyde Bailey (1858–1954).

This Article, making provision for the cultigens of horticultural nomenclature was to remain in the Botanical Code (with a minor amendment in 1935 suggesting the use of the letter 'c' before the horticultural name and antedating formal recognition of the cultivar) through 1906, 1912 and 1935 until the separation, in 1953, of the Horticultural Code, precursor to the International Code of Nomenclature for Cultivated Plants (Cultivated Plant Code). In 1900 there was the first International Botanical Congress and in 1905 at the second Congress in Vienna an agreed set of nomenclatural rules was established, the Vienna Rules, which became known from then on as the International Code of Botanical Nomenclature (now the International Code of Nomenclature for algae, fungi, and plants). After World War II the responsibility for the Botanical Code was taken up by the International Association for Plant Taxonomy and meetings to discuss revisions are held at six-yearly intervals, the latest being in 2005.[52]

In horticulture at this time there existed all the problems that had confronted botanists in the 19th century – a plethora of names of various length, written and published in many languages with much duplication. The period between 1867 and 1953 was an uneasy time in which American horticulturists and other groups in Europe, such as the specialist orchid community, made attempts to put order into this chaos within their particular group of interest and devising their own rules for naming the plants of commerce. Friedrich Alefeld (1820–1872), who used Latin variety names, in a monographic study of beans, lentils and other legumes distinguished three infraspecific taxonomic categories: Unterart (subspecies), Varietäten Gruppe and Kultur-Varietät, all with Latin names.[53] In doing this he was probably laying the ground for the later establishment of the cultigen classification categories cultivar and Group. In conjunction with the Brussels International Botanical Congress of 1910 there was an International Horticultural Congress having a horticultural nomenclature component.

As a result of general dissatisfaction and a submission from the Royal Horticultural Society the Règles de Nomenclature Horticole was established.[54] The use of simple descriptive Latin names (e.g. compactus, nanus, prostratus) for horticultural variants was accepted and so too were names in the local language – which were not to be translated and should preferably consist of one word and a maximum of three. This first Horticultural Code consisted of 16 Articles. With the intercession of a World War I it was not until the 9th Horticultural Congress in London in 1930 that the rules of a Horticulture Nomenclature Committee were agreed and added as an appendix to the 1935 Botanical Code. The rules established in 1935 were accepted but needed to be extended to include the cultigens of agriculture and forestry, but it was only a result of discussions at the 1950 International Botanical Congress in Stockholm and the 18th International Horticultural Congress in London in 1952 the first International Code of Nomenclature for Cultivated Plants was published in 1953. The American horticultural botanist Liberty Hyde Bailey was responsible for coining the word cultigen in 1918[55][56] and cultivar in 1923,[57] the word cultivar only coming into general circulation with the new Code of 1953. The use of these two terms belies the multitude of classification terms and categories that had been suggested as designations for cultigens.[58][59]

The first Cultivated Plant Code (Wageningen), which was published in 1953, has been followed by eight subsequent editions – in 1958 (Utrecht), 1961 (update of 1958), 1969 (Edinburgh), 1980 (Seattle), 1995 (Edinburgh), 2004 (Toronto) and 2009 (Wageningen).[60]

Following the structure of the Botanical Code the Cultivated Plant Code is set out in the form of an initial set of Principles followed by Rules and Recommendations that are subdivided into Articles. Amendments to the Cultivated Plant Code are prompted by international symposia for cultivated plant taxonomy which allow for rulings made by the International Commission on the Nomenclature of Cultivated Plants. Each new Cultivated Plant Code includes a summary of the changes made to the previous version and these have also been summarised for the period 1953 to 1995.[19]