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Plant classification is more of an art than a science

Adrian D Middleton
Certificate in Plant Studies
Plant Classification and Taxonomy Module
November 1994

What is Science?

sci'ence , n. 1. Knowledge (arch.), ... 2. Systematic and formulated knowledge (moral, political, natural, etc., ~, ...); ... [1]

In its broadest sense, science means 'knowledge', generally knowledge based on observation of the real world. Within the scientific disciplines (even in such uncertain ground as 'political science'), data is gathered, theories devised, and experiments or further observations used to test those theories

The key to progress is the ability to find structure or unifying principles within the mass of quantitative or descriptive data. Intuition, genius, hunches and guess-work are important factors in this process.

'Every schoolboy knows that science advances by logical orderly steps, and that progress is made by a systematic process of observation, hypothesis and experiment. Every schoolboy is wrong. Science advances is a series of random leaps, often based on intuition and guess-work.' [2]

In the classic 'scientific method' this leads to the 'hypothesis' which is then rigorously tested. Or not! In many cases the 'method' stops at this point, and it is left to later workers to show that something else is nearer the truth, or nearer to a new world view of the truth. No theory can ever be proved to be correct - it can only be proved incorrect, and it is only the absence of negative evidence that leaves many theories unchallenged.

The purpose of the theory (hypothesis, structure, or whatever) is two fold. It provides 'explanation' - why things happen(ed); the relationships between things - and aims at 'prediction' - what will happen; can we make things happen; what is still to be discovered.

Plant Classification

Plant classification certainly falls within the scope of science. Even in its earliest forms, it was based on observation and practical criteria - is the plant harmless/harmful/edible/useful? - and such arrangements sufficed through the middle ages when knowledge was limited and was influenced as much by superstition and folklore as by observation and experiment.

In the 17th century workers began to adopt a more structured approach. L'Obel arranged the plants according to his own system based on the physical appearance of the plant's foliage [3]. Workers each adopted their own system, or adapted others; names were long and descriptive; and there was little agreement on what constituted a single 'type' of plant.

Tournefort, Ray and Linnaeus are credited with many of the advances which led to modern classification. Ray attempted to produce a 'natural' system using a combination of characters, recognised the difference between environmental variation and inheritable characteristics, and that only the latter are valid for establishing a classification. Tournefort took a narrower view, concentrating on the features of the flower.

Which brings us inevitably to Linnaeus. His work is largely based on Tournefort, Ray, and others. Having considered 'natural' systems such as Ray's, Linnaeus adopted a system based on the reproductive organs of plants - e.g. numbers and positions of stamens - similar to ideas published by Camerarius in 1694 [4]. His system was essentially artificial, since it ignored many other plant characters, but had the advantage of simplicity.

'An artificial classification is based on purely arbitrary criteria. It is, as it were, imposed on the organisms from without. By contrast, a natural classification is one which exists already within the framework of living things, only waiting to be discovered.'

'... a purely natural system of classification is an ideal to be aimed at ...'[5]

The Linnaean system provided the basis for orderly changes as new knowledge became available; changes which affected the three aspects which together constitute 'plant classification' - identification, naming and organisation.

Identification

The basis of Plant Classification is the species, but its definition has to contend with variations due to environment and features such as sexual dimorphism as well as similarities arising from parallel evolution in unrelated groups.

External morphology has traditionally provided and continues to provide the primary criteria, but this now takes its place alongside new techniques. The microscope and scanning electron microscope have extended morphology to include hair patterns, seed coatings and pollen wall ornaments. They also provide access to the internal anatomy of the plants, and have created new disciplines such as palynology (pollen), embryology (fertilisation and seeds), cytology (cells) and the study of chromosomes [6].

Beyond the microscope, chemistry distinguishes similar plants, but also brings together species whose morphology previously placed them in separate groups.

With more data, botanists have been able to refine their definition of species, but not to achieve complete agreement. The 'lumpers' and 'splitters' [7] take opposite views where variations are seen between closely related populations. Darwin hoped that 'The endless disputes whether or not some fifty species of British Brambles are good species will cease' [8]. At the last count there were 240 such species - or just one if you are a 'lumper'.

'I tend to believe that the predilection for 'schizotaxia' [generic splitting], especially where new phyletic insights are not apparent, is largely a phenomenon of the personality: a belief that somehow future workers will esteem generic erections (and hundreds of new combinations, all with the maker's appended names) as an indication of precocious visionary versatility; as if the coining of a name in itself provided evidence for the brilliance that perceived the need.' [9]

Identification is only one aspect of classification, but is the primary concern of many laymen and professionals. To this end, many workers have devised 'Keys' which allow observable, usually morphological, characteristics to be used to 'home in' on a name to attach to a specimen.

Naming

'What's in a name? That which is called a rose,
By any other name would smell as sweet;
So Romeo would, were he not Romeo call'd.' [10]

Any system of classification demands a method of naming and any method is arbitrary - the names are only labels which allows us to communicate effectively.

'What's your dog's name?'

'I don't know. We call him Rover.' [11]

The lack of progress in plant classification before Linnaeus can be blamed in part on a lack of data and of development in the sciences, but also on the absence of a consistent naming standard. The names used in the herbals and the flora of the 17th century were essentially descriptive (e.g. Rosa Provincialis major flore pleno ruberrimo (~the very red Rose of Provence with big flowers) [12]) and were not consistently used - a situation analogous to common names which vary with locality and across barriers of language.

With the binomial system Linnaeus again reflected ideas from earlier workers, and laid the basis for future work. Formal rules were drawn up by de Candolle after the Paris congress of 1867 and have been though a process of constant change ever since. The refining of these rules (the International Code of Botanical Nomenclature - the 'Code') have led to major changes, most recently the renaming of entire family structures.

'Frequent changes in plant names have brought plant classification into disrepute among plant scientists working in areas other than taxonomy ... who know little of the compulsions imposed by the Code. ... It is ironical that the Code formulated to bring about stability in plant nomenclature has itself become a leading source of instability.' [13]

Organisation

'Of course, classifications are man made and may be designed to suit man's convenience or reflect his primary interest in plants. ... [they] are not necessarily natural entities.' [14]

The binomial naming system introduces the idea that species can be grouped within a 'genus'. Beyond the genus further levels of similarity - family, etc. - can be considered to be man made and subjective - simply a necessary filing system. The modern view, however, (since Darwin) is that they should reflect the underlying evolutionary relationships between the present day species.

'... a classification that expresses their evaluation of relationships among plants and thus reflects the course of evolutionary development.' [15]

Evolutionary change has resulted in differences within closely related species, but as more characters are utilised, degrees of similarity can be established. Knowledge and opinions will continue to change, and with them classifications which will always be based on incomplete data (note '... their evaluation ...' in above quote).

'We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganised. I was to learn later in life that we tend to meet any new situation by reorganising, and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency and demoralisation.' [16]

Today's accepted classification is essentially one view among many, and attempts to express our current understanding of the plant world. It is a tool to be used and to be adapted as it is used, which means that it will remain inherently unstable.

'Classification is not an end in itself but an attempt to present a current summary of our knowledge of plants.' [17]

What about Art?

art, n. Skill, esp. human skill as opposed to nature; skilful execution as an object in itself; skill applied to imitation & design, as in painting etc.; ... ; black ~, magic; practical application of any science; industrial pursuit, craft; ... [18]

At one level 'art' can be taken to include almost any human skill, but in common usage it generally refers to some sort of representation - painting, sculpture, music, literature, etc., the emphasis being on abstraction and imitation - producing something which is not the thing itself.

Art is a search for essential features - not unlike plant classification. It (art) is inevitably subject to the trends of fashion and opinion, and to the 'cult of the personality', and science in all its forms in not much different. Though many would argue that the quantitative - the exact - sciences are objective, the interpretation of results and the intuitive leaps which move the subject forward are the work of individuals who are subject to pre-conceptions and prejudices - and to inspiration and influence. It can be said that they also develop their own 'art forms' - elegance and symmetry often being seen as features of the best theories and discoveries.

'Art is a changing of the actual order and proportion of things, so as to bring out more forcibly than might otherwise be done that feature in them which appeals most strongly to the idiosyncrasy of the artist.' [19]

Conclusion

'The rather uncharitable remark that [taxonomy] is an 'art', implying that there is no scientific merit in [it], does not bear examination. ... Certainly, the competent taxonomist displays an artistic talent, an intuitive flair ...' [20]

The above quote displays a narrow view of both art and science. Plant classification is certainly based on science and scientific techniques, yet, as with any science, it also carries features which we attach to art - notably that of 'abstraction'. Though the mass of data is always incomplete, it is necessary to decide which parts are 'essential' and to produce from them a representation which clarifies the underlying structure.

'Taxonomy is a scientific art intended to bring order into what otherwise would be untidy and disorderly.' [21]

The use of plant classification can also be regarded as an art - a skill - involving the ability to take from it what is useful in a given context - classification being only a tool. Given the moving target presented by changes in naming and advances in our knowledge, many would argue that rather than being an 'art', perhaps it should be regarded as a 'mystery'.

mystery, n. Hidden or inexplicable matter; make a ~ of, treat as a secret; secrecy, obscurity, as is wrapped in ~ ; (practice of) making a secret of (unimportant) things; religious truth ...... [22]

But that's another essay ...

References and Notes

[1] The Concise Oxford Dictionary.

[2] Horobin (?), 'Science is God', 196? - quoted from memory.

[3] L'Obel, Plantarum seu Stirpium Icones, mentioned in de Bray, 1989, p33.

[4] Camerarius, De Sexu Plantarum Epistola, 1694, mentioned in de Bray, 1989, p66.

[5] Vines and Rees, 1975, p51

[6] Sivarajan and Robson, 1991, ch 8.

[7] Sivarajan and Robson, 1991, p216

[8] Darwin, On the Origin of Species, 1859, - quoted in Briggs and Walters, 1969, p32.

[9] B L Turner 1985 (summing up proceedings on Symposium on 'Generic concepts in the Compositae' - quoted in Sivarajan and Robson, 1991, p216).

[10] Shakespeare, Romeo and Juliet, II, ii.

[11] Anon

[12] Plate from The Catalogus Plantus 1730 in de Bray, 1989, p63

[13] Sivarajan and Robson, 1991, p215

[14] Greulach and Adams, 1976, pp34,37.

[15] Greulach and Adams, 1976. pp34-35.

[16] Caius (or Gaius) Petronius - ? Petronius Arbiter (d. ~ 65 AD).

[17] Greulach and Adams, 1976, p37.

[18] The Concise Oxford Dictionary.

[19] Thomas Hardy (from Florence Emily Hardy 'The Life of Thomas Hardy 1840-1928' 1962).

[20] Sivarajan and Robson, 1991, p11-12.

[21] Cowan - quoted by Patrick Harding in lecture on Plant Classification.

[22] The Concise Oxford Dictionary.

Bibliography

Briggs D and Walters S M (1969). Plant Variation and Evolution. World University Library.

de Bray, Lys (1989). The Art of Botanical Illustration. Helm.

Greulach V A and Adams J E, (1976). Plants - An Introduction to Modern Biology. Wiley.

Sivarajan V V and Robson N K B, (1991). Introduction to the Principles of Plant Taxonomy. CUP

Vines A E and Rees N, (1975). Plant and Animal Biology - Vol 1, 4th ed.