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Plant classification

CONTEXT

See the general introduction to plants and people

There is a sense in which all our cognitive activity is taxonomy. We operate in the world using mental and physical objects or categories which we group in various ways and rank in some order according to our particular purpose. The groups we create become, in turn, mental objects or categories in a complex system of parts and wholes. Much of human intellectual history has been occupied with the refining (adding to, removing, combining, reconfiguring) these groupings. Sometimes these objects seem physically distinct like individual human beings or plants; sometimes they seem less physically distinct, like the colours of the rainbow; and sometimes they seem completely subjective or abstract like happiness or the idea of rank in biology.
The article on plant classification tackles the way we mentally structure the plant world bearing in mind that scientific classification is just one way of organizing the world of plants and that although we seem to have a clear understanding of what constitutes and individual plant the idea of a species is a matter of some controversy: are species real entities existing in nature, or are they creations of the human mind, or something else?

The article plants and people described the difficulty of knowing where to start when studying this relationship. Unlike scientific disciplines this topic has no formalized categories of study that are organized into meaningful groups that under continual refinement by a community of like-minded participating investigators. There is no agreed starting point of categories, principles, theories and procedures – a process of mutually acceptable classification.

This article, then, looks at the major ways that we do classification – by classifying the ways that we classify – the way we segregate the world into meaningful units, and how these units are then organized into meaningful groups. It then applies this knowledge to the formalization of a study of ‘Plants and People’.

This is both a conscious and unconscious mental processing of the world that is going on in our heads all the time.

CLASSIFICATION

By ‘classification’ is meant the ordering or grouping of objects according to specific criteria to achieve some goal. The study of classification in general, its principles and procedures, is called taxonomy.

Classification is so much a part of our lives that the terms we use to describe it are many. The objects of the classification we might refer to in general terms as taxa, the taxonomic units or things being classified, and they can vary from physical objects like animals and plants to mental objects like ideas or concepts. For simplicity we can refer to the units of classification as ‘categories’ and the purposive or goal-directed character of our mental processes is often referred to as ‘intentionality’.

Classification allows us to impose order on the world by prioritising or ranking the objects of our thought. Intentionality can be an unconsious processs as occurs with our visual and auditory perception, but whether it is conscious or not can be a matter of degree. When we choose between different cheeses at a delicatessen we are aware of our mental process of choice but it is generally very quick, when the process of comparison becomes more laboured and considered we tend to call it ‘reason’.

At present my attention has settled on writing this article but soon it might be diverted by a visitor or the desire for a cup of coffee as my body responds to prioritising factors in my internal states and external circumstances. But when these diversions are satisfied my focus returns to the computer screen and the selection (prioritization, classification) of possible words that I can use and and their order within a sentence. Clearly, at any given moment, we are employing multiple prioritizing processes to do with the way we think and feel.

In summary, we are constantly classifying the objects of our experience, or categories, according to particular criteria based on some purpose or goal. This is an innate human characteristic, since it is used by all human beings to guide their action, and it happens with varying degrees of consciousness. When it is a fully conscious process we refer to it as ‘reason’. Clearly the success of any classification depends on the extent to which it achieves the purpose for which it was designed. This may be conscious purpose, as when we reach the solution to a mathematical problem, or unconscious purpose as when our eyes move to the source of a noise.

Origins of taxonomy

Classification begins with the pre-conscious structuring of our experience. This is the way that we intuitively relate to the world – the way that we innately experience the world before conscious deliberation begins. It is also this that determines our metaphysical intuitions about the way things are in the world– the way we represent the world. As an innate faculty it is also, of necessity, part of the human experiential umwelt[1] – our reality – the way that we humans share a uniquely human collective experience of the world.

The human umwelt

Baltic German biologist Jacob von Uexkull (1864 – 1944) named the environment of significance to any organism for its survival and wellbeing – not its environment as viewed by a human – its umwelt. This is, as it were, the organism’s species-specific frame of reference, the perceptual world in which an organism exists and acts as a subject responding to sensory data. For example, a tree uses light for photosynthesis, we use light to see. The idea of of an object’s sensory frame of reference is closely related to the notion of autopoiesis.[2]The innate mental faculties of special interest to us here are those of mental structuring segregation, focus

Much of our cognitive activity is taxonomy: without the constant ranking and classification of the objects of our mental life it would not be possible to operate in the world.

The world is meaningful place only because our minds are constantly ordering the multitudes of images, ideas, emotions, sensations and other representations that are passing through our brains. Much of this goes on unconsciously as innate computation but some of this processing requires conscious effort.

To cope with the flood of incoming sensory information our brains segregate the world into meaningful objects, focus on a limited range of these objects at any given time, and organize them into meaningful groups according to our conscious or unconscious intentions. The outcome is that we experience the world not as a chaotic maelstrom of competing sensations but as a unified and coherent experience. Clearly the ability to order the world like this is an evolved and innate biological characteristic, while the particular human way that we experience the world is a uniquely human biological characteristic . . . part of our human nature.

Mental objects form a complex system of parts and wholes that makes up the web of mentally connected categories that are often ranked into an order of priority to serve our temporary intentions.

Much of human intellectual history has been the refinement (adding, removing, combining, reconfiguring) of categories that we pass on to future generations through language. Sometimes the physical referents of these mental categories appear distinct – like individual human beings or plants. Sometimes they seem less physically distinct, like the colours of the rainbow. And sometimes they seem completely subjective or abstract like the concept of happiness, the centre of gravity, or a shared property like ‘tallness’.

Classification & purpose

It is safe to assume that the units of our mental life emphasize those objects that have been of importance to us in the course of our evolutionary history. This world of human experience, both mental and physical, has been conveniently referred to as our umwelt[1] or ‘human-centered world’ – our ‘reality”. Organisms can, of course, have different umwelten, even though they share the same environment: they can have different ‘realities’.

Classification systems are products of our minds as we group mental categories in myriad different ways. Being purpose-driven the particular classification we use will depend on the purpose for which it was derived. So, for example, we might classify plants according to the way we use them for food . . . dividing them into cereals, fruits, nuts, vegetables and so on. In ancient times great respect was given to those possessing the specialist knowledge of the medicinal properties of plants.  So we can identify a rough historical line of descent from shaman or medicine-man, to priest, to apothecary, physician, to today’s botanical academic or plant scientist. But medicinal use is just one of many possible plant uses or purposes: there will, of course, be as many different plant classifications as there are different plant uses.

Is any one of these classifications to be preferred over others?

Scientific classification

As scientists we give special credence to scientific classification because it lives up to the Theophrastian ideal of objectivity by reflecting plant relationships to one-another. Before Darwin this was determined by measuring mostly morphological similarities and differences. After Darwin every means possible was used to determine evolutionary relationships as descent with modification.

But in terms of the existence of plants on planet Earth, scientific classification is one small part, the study of plants must be much wider than this: it is much more than the study of plant classification.

Scientific classifications are also designed for a purpose: to reflect or map the natural world. So, for example, botanists make a very clear distinction between artificial plant classifications such as those based on flower colour or edibility (a subjective classification) and natural classifications based on flower structures that reveal the evolutionary relationships of plants (much more objective). A useful biological classification, by accurately mirroring what exists in the world, facilitates prediction and inference as to, say, the history of the objects it contains.

It turns out that the classification systems used in science are not unique to science – they are universal. What then are the various ways of classifying things – what are their goals, structural properties, strengths and weaknesses?

Theophrastus’s division of plants into ‘herbs, shrubs, and trees’ was a practical classification that persisted into the 18th century. Today formal scientific classification groups plants in relation to one-another in terms of their presumed evolutionary (phylogenetic) history, sometimes known as phylogenetic systematics. The one-time morphological characters observable with the naked eye have been supplemented by microscopic and chemical-genetic information that is analysed using complex computer algoriths. Classification that concentrates on genetic characters is referred to as molecular systematics.

It is virtually impossible today to define what we mean by ‘science‘, but one devious way would be to say that it is the refinement of the classification of all those categories that we use in the field of activity that we refer to as ‘science’. So, for example, science is involved with the classification of physical objects like animals and plants. But science is much more than the classification of physical objects it also deals with more mental categories like names, laws, hypotheses, definitions, principles, theories and so on, and part of the scientific process is the refinement or improvement of these categories as well.

Classification systems

Are there different kinds of classification – different ways of organizing units into groups?
A diversion into the methods of taxonomy will help us here.

Hierarchies

Many classification systems exhibit some kind of hierarchy, that is, they rank or prioritize their objects so that related objects are arranged in metaphorical levels, like the rungs of a ladder with a ‘top’ and ‘bottom’.

Nested hierarchies

In a strict nested hierarchy the groups are contained within other groups like a Russian doll that can be opened to reveal a smaller doll and so on. A scientific example would be the Linnaean biological classification or organisms into orders which contain families which, contain genera, which contain species . . . and so on. Knowing a plant has the species name Lactuca sativa, Lettuce, connects us to a vast store of its associated historical and biological information.

Strict hierarchies like this have several important properties:

Inclusivity – they are progressively more inclusive as ranks go from bottom to top

Exclusivity – an item in a strict hierarchy can only belong to one group at a particular ‘level’ or rank.

Transitivity – the properties that define the objects at higher ranks pass on to the lower ranks

Clear boundaries – the properties defining group membership at a particular rank must be both necessary and sufficient

An example of transitivity would be that all vertebrate animals (Vertebrata) have a vertebral column no matter how they are subsequently subdivided; sub-groups though resembling one-another by sharing the properties of ‘higher’ groups nevertheless differ in the properties that uniquely define them, so Homo sapiens as a species shares the property of being human as expressed in the genus name Homo but it differs from other species of human by being H. sapiens, the ‘Wize human’ there is thus both association and distinction) – the binomial (a name consisting of two words) expresses both similarity and difference at the same time

An example of exclusivity would be that Homo sapiens cannot be, at the same time, Homo heidelbergensis.

Strict nested hierarchies require clarity about similarities and differences between groups. Hierarchical definitions express both affinity and distinction in an economical way. Transitivity allows the hierarchical structure to build up useful information that is useful for prediction, while the inclusivity – the containment of groups within groups demonstrates the evolutionary principle of descent with modification.

The formal structure of nested hierarchies works well for items that can be clearly defined because they have unambiguous group boundaries. However, in daily life we use many categories with indistinct boundaries so the demand for mutual exclusivity cannot be met satisfactorily. In such cases the members of groups at a particular rank sharing family resemblance rather than fulfilling strict necessary and sufficient conditions – and some items at a particular rank may share closer resemblance than others.
Further, limited knowledge can diminish the power and reliability of definitions and grouping items using more than one criterion can become unwieldy (say classifying plants based on both flower structure and fruit structure).

The effectiveness of a hierarchy in achieving its purpose will only be as good as the knowledge used in its construction and lack of clarity about items and their definition diminishes the power of transitivity.

Difficulties in creating clear categories in science are well known, for example, in the classification of rapidly-changing viruses or in defining the nature of particular smells.[Kwasnik, pp. 44-45] Descent with modification can itself lead to graded transitions rather than necessary and sufficient groupings (essentialism) as we try to impose logical order on graded nature.

Trees

Another kind of hierarchy is exemplified by military rank. This hierarchy has clear distinctions between groups (like private, sergeant and lieutenant) but there is minimal transitivity between the groups: there are no clear-cut characteristics shared by a private and a sergeant.

In other words trees lack inclusivity: though a species is a member of a genus which is a member of a family – a private is not a subdivision or kind of Sergeant who is, in turn, a kind of Lieutenant. A tree indicates a chain of command but does not include a clear definition of the nature of the authority.

Partitive hierarchy

A further kind of hierarchy is the partitive hierarchy. A partitive hierarchy might arise, for example, when we subdivide a geographic region. Melbourne is a part of Victoria which is a part of Australia. This is an inclusive hierarchy (though Victoria is not a kind of Australia it is a part of it) where certain properties are shared.

Partitive hierarchies share, with nested hierarchies, the characteristic of passing from the general (the most inclusive domain) to progressively smaller or less inclusive parts. But note that a simple confusion can arise here. Objects that share the characteristic of just being part of something can be quite different in general character: an apple core, a train ticket and bottle may all be parts of the waste bin while, in a nested hierarchy of animals we know that those animals that are vertebrates will share certain similarities.

Trees require a knowledge of the characteristics of the items being classified. The structure of the tree will be determined by the nature of the relationship between the parts: part-whole; cause-effect; process-product; start-end etc.

Trees organize categories in a way that defines how they are related and/or the degree to which they are related (spatially, metaphorically), and/or the relative frequency of items within a particular category. However, a tree is constrained by the order in which distinctions are drawn and this may require subsequent modification.

In a hierarchy the information flows (metaphorically) not only ‘upwards’ and ‘downwards’ between levels, but ‘laterally’ between items at the same level.

In trees the ‘lateral’ categories might contain very different objects so they tend to be strong along only one dimension of interest and are not so effective at representing multidirectional complex relationships. As with hierarchies the choice of key defining characteristics can be a matter of dispute and trees allow only partial inference.

It is important to be aware of the strengths and weaknesses of these forms of classification. Each method has its own goals, structural properties, strengths, and weaknesses. New knowledge might initiate the formation of new classifications but classifications may themselves contribute to knowledge generation. This occurred, for example, with the prediction of new and, as yet, undiscovered elements and their properties following the construction of the Periodic Table, and the new classifications and categorisation resulting from new scientific technology, as with: carbon dating, DNA analysis, remote sensing, radio-astronomy, the crystalline structure of gems rather than their hardness and so on.[Kwasnik, p. 43]

The goal of these classifications, like that of all science, is to maximise representational power.

Progressive classification

One advantage of viewing science as category improvement is that it encompasses all scientific activity and shows how this activity can improve over time as it helps us describe and understand the world in more efficient and effective ways.

Not all classifications are progressive. Going shopping requires all kinds of mental ordering of our purchases but we are not making scientific progress. The advantage of scientific categories are that they are shared (not individual or personal) categories whose refinement is a matter of broad agreement within the community of scientists.

There have been, throughout history, obvious practical ways of improving our scientific categories through progressive classification – as in the discrimination of ever smaller particles of matter – and ever larger expanses of space. Biologically we have achieved an ever finer resolution of the numbers, kinds, geographic distribution, and evolutionary relationships between the organisms of the world.

Progressive scientific classification has been so successful that we might assume it is in some way a more accurate, reliable, and predictive form of classification: that, of all systems of classification, scientific classification is the best. But this could be a mistake, and a look at scientific plant classification will tell us why.

PLANT CLASSIFICATION

The outline of classification given above showed that we classify objects in all sorts of ways using classification criteria governed by the purpose for which the classification was designed.

Even so, it is conventional among biology students to understand plant classification in a narrow sense as a way of grouping plants according to how closely they are related to one-another.

In Linnaeus’s day, in the mid 18th century, when most people believed that each species was uniquely created by god, the relationship was judged in terms of the overall similarities and differences in plant characters and classifications based on these characters were called natural classifications. However, sometimes it was easier to group plants according to simple characters like flower colour, this way of grouping plants on characters of convenience being called an artificial classification. Linnaeus himself used a system of artificial classification based on the number of stamens and styles in the flower.

When Darwin published On the Origin of Species . . . in 1859, the meaning of natural changed. Biological classifications became progressively focused on hypothetical evolutionary relationships, not just superficial resemblance. As it happened, those organisms with similar characteristics were also closely related evolutionarily (except in the case of parallel evolution) and Darwin’s theory, which pointed out that all organisms likely arose by descent with modification from a single organism, fitted neatly into Linnaeus’s classification hierarchy of boxes within boxes – species within genera, within families and so on.
This is a progressive classification that has been constantly refined throughout history.

Plants themselves

A giant leap in the study of plants was taken in ancient Greece. This, so far as we can tell, was the true dawn of plant science when Theophrastus, who followed Aristotle as Head of the Lyceum in ancient Athens, recognized that for all prior history people had investigated plants from a human perspective, classifying and studying them according to their uses . . . as food, medicine and so on. This was the study of plant utility, of plants as a human resource, and classifications therefore emphasized the utilitarian criteria used in their construction. Theophrastus’s great insight was that plants could be studied for their own sake . . . their structure, function . . . and their relationship to one-another, and their environments . . . without regard to human interests.

Detachment from human concerns is often regarded as an indication of sound science. For nearly 1600 years after Theophrastus it would be the study of plant morphology and identification that would exemplify this scientific approach to plants but it was still generally also allied to utilitarian medicinal properties. Though questions about plant function and interaction with the environment were asked, it would be some time before carefully reasoned scientific answers would be given.

So, the scientific classification of plants was devised (in line with the original intentions of Theophrastus) to study the similarities and differences between plants themselves so as to organise them as efficiently as possible into groups based on their physical characteristics. The historical record suggests that Theophrastus was among the first to study plants both in terms of their relation to humans but also with special emphasis on their relation to one-another.

The purpose or goal of scientific plant classification is therefore to ascertain the number, kinds, and relationships between the world’s plants. This scientific endeavour was at its most pressing during the Ages of Discovery and Enlightenment when Europeans were mapping the physical boundaries of the world’s continents, no doubt an incentive to accelerate the inventory of the world’s biota. At that time the economic and cultural potential of the world’s unknown plant resource was of foremost concern. Plants like spices had made men fortunes and given some countries power over others.

Historical development

In the course of history increasing numbers of characters were used to map, with ever finer resolution, the similarities and differences between different kinds of plants.

But to take on the universal character of a science, botany needed a community of communicating botanists with a commonly accepted terminology, method of plant inventory and description, including agreed systems of nomenclature and classification. In the modern era it took over 200 years to develop these scholastic tools whose integration into an internationally-acceptable system was the great achievement of Carl Linnaeus.

The subsequent refinement of plant classification using progressive developments in technology has created greater discriminatory precision, predictive power and in this way contributed to both progressive and cumulative plant knowledge.

Historically the classification of plants can be divided into four phases:

Habit

From about 300 BCE to about the middle of the 18th century plants were grouped together according to their habit as trees, shrubs, herbs and so on. The purpose of the classification was to group plants according to simple and obvious characteristics of the plants themselves rather than any particular utility they might have for humans.

Artificial classification

During the 18th century with a more universal terminology that included a broad range of plant parts the selection of possible characters became more elaborate as plants were further divided using a system of artificial classification which used just a few simple and convenient characters that facilitated plant identification to a finer resolution of entities. The best known of these artificial systems was the ‘sexual system’ of Linnaeus which grouped plants according to the numbers of flower parts is frequently quoted. The selection criteria, though based on differences between plants themselves, were nevertheless practical characters of human convenience.

Natural general-purpose classification

As plant knowledge rapidly increased towards the end of the 18th century this artificial system was further refined using a much larger set of characters so that more emphasis was placed on characters that emphasised similarities and differences between the plants rather than characters that were simple and practical to manipulate. This became known as natural classification because it grouped plants according to the way they seemed to be in nature. Botanists were no longer imposing order on the plant world by using an arbitrary human choice of convenient characteristics, instead through the close examination of many characteristics they were discovering the order that existed within nature itself. Plant taxonomists like Linnaeus now believed that the order they imposed on the plant world reflected order that actually existed in nature. They were discovering the ‘natural order’ that had been placed in the living world by God.

This is sometimes referred to as a general-purpose (phenetic) classification since all characters are taken into account t to give an overall reflection of similarities and differences – no character is regarded as more important than any other.

Flowering Plant Phylogeny diagram
Flowering plant phylogeny as at 2020
Including the currently recognized 435 plant families

The colours of the branches and the outer circles represent the major angiosperm clades (branches of the plant evolutionary tree) as indicated in the caption (ANA, Amborellales + Nymphaeales + Austrobaileyales). The illustrations around the circumference show 32 plant families and their position in the tree.
Courtesy public domain license. Adapted from the originals provided by S.M., the Peter H. Raven Library/Missouri Botanical Garden and the Mertz Library/New York Botanical Garden

The flowering plants (angiosperms) arose in the Early Cretaceous about 145–100 million years ago, supplanting the earlier ferns and conifers (pteridosperms and gymnosperms). Palaeobotanical evidence indicates that this replacement was gradual, flowering plants not becoming dominant until the Palaeocene about 66–56 million years ago. The timing, geographic sequence, and plant composition of this diversification remains uncertain. There appear to have been substantial time lags, mostly around 37–56 million years, between the origin of families (stem age) and the diversification leading to extant species (crown ages) across the entire angiosperm tree of life. Families with the shortest lags occur mostly in temperate and arid biomes compared with tropical biomes. The ecological expansion of existing flowering plants, it seems, occurred long after their phylogenetic diversity originated during the Cretaceous Terrestrial Revolution.

Phylogenetic special-purpose classification

After the mid-19th century and the advent of Darwin’s theory of evolution by natural selection classifications acknowledged the relationship between plants as descent with modification from common ancestors, this form of evolutionary or phylogenetic scientific classification using all characters that might serve as evidence and being based on the assumption of genetic ancestral relationships. God was no longer a necessary aspect of this world view.

In determining phylogenetic relationships some characters become more important than others. The vertebrates are, unsurprisingly, united in their branch of evolution by possessing vertebrae.

From botany to plant science

Today the imperative for scientific classification is much reduced. Though there is always more work to be done in classifying the natural world and the foundational units of its ecology, discovering, naming, describing, and classifying new species, the urgency of the task for global inventory is less than it was in, say the eighteenth and nineteenth centuries. Today our interests and concerns with the natural world have taken a new turn. The world that was wild and unknown to Europeans at the time of the Age of Discovery is now mostly converted to human use and we are uncertain about the consequences of this short-term environmental transformation fo rthe future of humans, the community of life, and the planet. Human influence on the planet has been so great as to name the latest geological period the Anthropocene in acknowledgement of global human impact on the planet.

Historically we can see how the purpose of plant classification became preoccupied with scientific clasification so that there would be some shared means of ordering the biological objects of the world, but with the practical consequence that this classification could be universally applied to agriculture, horticulture and forestry. So even scientific classification was ultmately a matter of utility. Today our primary cultural concern is with our future which we need to make sure will be sustainable. Today there is a strong argument that we should be developing the best possible plant classification for the purpose of sustainability. The categories we would use for such a classification would relate plants not to one-another but to people and sustainability.

Of course we already do this in a general terms but what would such a clasification look like if we applied to it the same rigour that we do to scientific classifications?

Sustainability classification & nested hierarchies

We have, of course, devised plant classifications in all of the above categories but not, perhaps, with the degree of dedication that we have applied to formal scientific classification. Scientific plant classification organises plants in a boxes within boxes way such that no plant can be a member of more than one group: the plants are ranked into families, which are then divided into genera, divided in turn into species, and so on. The specific criteria used to group the plants are their physical characteristics, and the classification becomes progressively inclusive. There are over 350 plant families and over 350,000 species. An example of the way this works would be the single category ‘seed plants’ which is then divided into the groups ‘flower-bearing plants’ and ‘cone-bearing plants’. The flower-bearing plants can then be divided into those which have one seed leaf (monocotyledons)
and those which have two seed leaves (dicotyledons).

So how would we divide and subdivide plants based on criteria of sustainability? Ideally we would start with the most general characteristic of sustainabilty and proceed to mutually exclusive items of lesser significance. The characters used to establish major groupings of seed plants – whether the plants have flowers or cones – are uncontroversial and mutually exclusive. The organisation and justification for sustainabiity categories within the idea of sustainabilty are discussed elsewhere. Here is a list of useful categories frequently associated with the discussion of sustainability: social organisation, population, biophysical resource consumption, technology, transport and communication, materials, energy, food, water, biodiversity.

A number of problems immediately arise. Firstly, sustainability is itself an imprecise idea so creating a universally accepted and stable definitional category would be difficult. Secondly, there is the intrusion of value as subjectivity which in scientific classifications is reduced to an absolute minimum. However we define sustainability it relates to environmental impact and how that impact occurs will be both causally complex and value-laden. Environmental costs must be assessed against benefits. There is the further complication that because of the complexity of sustainability the development of neatly mutually exclusive groupings is unlikely.

We can examine sustainability obliquely by categorizing the many ways that humans use plants. For example, the many plant categories that relate to their utility: use for agriculture, forestry, and horticulture; as food, fibres, medicines, poisons.
We use plants as food; food and drink additives; psychoactive plants; poisons; as medicines and drugs; fibres; dyes; perfumes and aromas; oils, fats, waxes; resins; rubber; wood and timber for fuel and paper; for structural materials, decoration, and ceremony.

We can also categorize plants more generally through the contextual idea of Ecosystem Services[1] which is convenient shorthand for the many ways in which humans benefit from nature. The overall goal is to maximize the well-being of humans as freedom of choice and action which is only possible by also maximizing the well-being of the community of life which entails care of the wider environment of planet Earth. There are several basic constituents of well-being: security (as personal safety, and maximum protection from political and natural disasters); access to basic material resources (jobs, food and goods, shelter); health (access to clean air and water, and medical attention); and good social relations through mutual respect and support. From this perspective, if we are to maximise human well-being then we need to know how Ecosystem Services contribute to the constituents of well-being. The Millennium Ecosystem Report[1] proposes four ways in which this can done: by provisioning (e.g. food or fresh water, materials), regulating (e.g. climate, flood, disease etc.), supporting (e.g. nutrient cycling, soil formation, primary production, pollinators), and finally cultural (aesthetic, spiritual, educational, recreational).

This draws our attention to several key points All plant classifications relate to human utility although scientific classification uses characters that are not necessarily so. plants can be classified in many ways with formal plant classification relating mostly to the plants themselves and other classifications relating mostly to human utility. Almost all classifications that we apply to plants relates to their utility; the prioritization of these methods of classification is itself a matter of conscious or unconscious prioritization or policy.

 

Plants, people, planet

This web site has as its central theme the role of plants, especially those in Australia, in the future of planet Earth. Plants and Australia are categories that lie within the grander theme of life, planet, people. Though people are part of ife their influence on the furure is overwhelming and therefore requires special attention.

We therefore need the best possible progressive classification through which to address this theme. The interrelated taxonomic units within this system are contentious and are discussed elesewhere, but stated simply here they are the physical objects plants, planet, and people. Their relationship as determined by the interaction of environmental, social, and economic processes. The goal of the classification, its purpose, is sustainability – which is the long-term mutual interdependence of all life-forms and their life-support systems. Life-forms are interdependant in such complex ways that singling out individual kinds for special treatment although humans are an obvious case and plants have been selected for special consideration on this web site.

Long-term survival of humanity depends on the protection of the organisms and ecosystems on which people depend. However, humanity is likely to place itself ahead of other species for survival. One way of protecting all life, but humanity in particular, has been expressed through the notion of ecosystem services: provision (food, wood, fresh water, fuel etc.); regulation (climate, floods, water purification etc.); culture (aesthetics, spirituality, education recreation etc.); support (soil formation, nutrient cycling, primary production etc.).

Sustainability operates at many scales: it therefore crosses several domains of discourse which therefore complicates the elucidation of causal connections.

 

Scale

One major difficulty to overcome is that of scale. On the one hand without plants there would possibly be no life – plant impact has been total and planetary-wide affecting all organisms. On the other hand particular individual plants can be of great importance to individual people, and not all aspects can be considered all at once. How are we to deal with the huge gulf between macro and micro scales of interest?

In the first instance we must try to trade the blandness but comprehensiveness of generality against the inaccuracy but utility of specificity. We need to find the best mix of these two forces.

Certainly one approach is to see how the plants on the surface of the planet have been altered in their composition and distribution by human activity.

The article on plant classification tackles the way we mentally structure the plant world bearing in mind that scientific classification is just one way of organizing the world of plants and that although we seem to have a clear understanding of what constitutes and individual plant the idea of a species is a matter of some controversy: are species real entities existing in nature, or are they creations of the human mind, or something else?

The taxonomy of plant taxonomy

Language provides us with a symbolic representation of the world. The concepts and categories that make up our language are, like the universe itself, linked into a web of interconnected knowledge. We need to ensure that the categories we use to organize this knowledge are the best-for-purpose that we can possibly produce. This is the task of science.

Knowledge grows cumulatively and to make an impact in any field of study a student must add to the fine detail of their particular discipline by refining existing categories and adding new ones. As students we can become enmeshed in our own particular region of the knowledge web. Proceeding by analysis and the desire to understand the fine detail we do indeed ‘learn more and more about less and less’ and as individuals it becomes increasingly difficult to establish a synoptic view of the intellectual landscape – something we desperately need to reassure ourselves that effort and resources are being directed towards the areas of greatest need.

PLANTS & PEOPLE

How would you organize a course of study titled ‘Plants & People’?

One aspect of scientific rigour is the breaking up of knowledge into areas of study as academic disciplines. These disciplines share categories, theories and procedures that are under constant refinement by the study’s practitioners who, through a shared literature, share their critical investigation of the key characteristics of their subject. So, for example, with the discovery of the microscope, botany added many new categories of microscopic structure to the subject and this provided further insights facilitating further improvement of the existing categories used to explain plant structure and function. Another aspect of scientific studies is that they have tended to proliferate over time as knowledge has accumulated and subdisciplines have emerged.

The relationship between plants and people has so far been treated in a piecemeal way: it has not been formalized in the way a scientific study is formalized.

In short, there would appear to be as many plant classifications as there are purposes for plants.

The grouping criterion used for scientific biological classification is evolutionary relationship (phylogenetic systematics or cladistics). Plant systematists today use elaborate molecular and genetic techniques to establish the evolutionary relationship between members of the plant kingdom. But plant science, loosely regarded as the study of plant structure and function, uses many other grouping criteria to organize plant knowledge – not just evolutionary ones.

A formal study of the relationship between plants and people requires, first, a set of key categories. It then needs to group these categories into pertinent areas of interest, recognizing that these may be many and varied.

Let’s look at what this overall plant picture or synthesis might be like by taking the widest possible view of plan-human relationship before narrowing the focus of analysis: it need not be controversial.

Analysis & synthesis

In approaching any subject it is sensible to begin with the broad context, with ‘setting the scene’ rather than immediately discussing the fine detail. For plants this is an overview of the place of plants in the scheme of life on Earth.

The basic questions about plants begin with the widest sensible context of space and time – which is the world over the period of existence of plants and – since we are especially concerned with plants and people – that period of plant existence that co-exists with humans. The most obvious question concerns spatio-temporal variation in numbers, kinds, and their distribution. Important here are the plants that have been of particular interest to humans . . . in effect, the cultivated plants. Addressing this question has been a long-term human enterprise that is now drawing to a close.

Boundaries of space & time

The stage on which plant existence has played out is space and time. So far as we know, plants have been spatially confined to planet Earth where they have been temporally confined to the last 3.5 billion years (flowering plants to the last 125 million years). In the most general terms, what we want to understand and explain is the origin of plants and the way they have evolved and diversified from their origin up to the present day.
Already we have encountered several wide-perspective subjects. We first need to develop an objective understanding of the objects we are dealing with (plant taxonomy), their physical change over time (plant evolution) and their spatial distribution over time (plant geography). In accounting for plant evolution and geography environmental factors must be taken into consideration (plant ecology). Here, then, are the four core subjects that give us a broad synthesis or overview of plant existence.
Plant taxonomy has been studied from the earliest days, including crude forms of scientific classification. Studies of plant geography and plant evolution are comparatively recent, plant geography gathering momentum with as Western European voyages of discovery and scientific exploration encompassed greater proportions of the world, and studies of plant evolution followed on the heels of Charles Darwin’s On the origin of species . . . . Ecology has been a late starter in academia. Though ecological observations have been made throughout history, the subject of ecology was only formally acknowledged in the 20th century.
The remaining process of analysis has spawned many disciplines budding off one-another with the accumulation of knowledge but all emanating essentially from questions of structure and function – of morphology and physiology, these again beginning to breed prolifically into new disciplines and subdisciplines from the mid-19th century on.

There is a sense in which all our cognitive activity is taxonomy. We operate in the world using mental and physical objects or categories which we group in various ways and rank in some order according to our particular purpose. The groups we create become, in turn, mental objects or categories in a complex system of parts and wholes. Much of human intellectual history has been occupied with the refining (adding to, removing, combining, reconfiguring) these groupings. Sometimes these objects seem physically distinct like individual human beings or plants; sometimes they seem less physically distinct, like the colours of the rainbow; and sometimes they seem completely subjective or abstract like happiness or the idea of rank in biology.

The article on plant classification tackles the way we mentally structure the plant world bearing in mind that scientific classification is just one way of organizing the world of plants and that although we seem to have a clear understanding of what constitutes and individual plant the idea of a species is a matter of some controversy: are species real entities existing in nature, or are they creations of the human mind, or something else?

The taxonomy of plant taxonomy

Language provides us with a symbolic representation of the world. The concepts and categories that make up our language are, like the universe itself, linked into a web of interconnected knowledge. We need to ensure that the categories we use to organize this knowledge are the best-for-purpose that we can possibly produce. This is the task of science.

Knowledge grows cumulatively and to make an impact in any field of study a student must add to the fine detail of their particular discipline by refining existing categories and adding new ones. As students we can become enmeshed in our own particular region of the knowledge web. Proceeding by analysis and the desire to understand the fine detail we do indeed ‘learn more and more about less and less’ and as individuals it becomes increasingly difficult to establish a synoptic view of the intellectual landscape – something we desperately need to reassure ourselves that effort and resources are being directed towards the areas of greatest need.

Cultivated plants

Cultivated plants encompass the important economic plants (economic botany) which include not only staple foods, mainly cereals (agriculture), but also the plants of orchards, vineyards, market gardens and plantations (horticultural crops). There is also the additional important histories of medicinal plants (pharmacognosy), herbs and spices as food additives (condiments), ornamental plants (horticulture) and timber trees (forestry). To this list can be added, in recent times, the group of cultivated plants that have escaped to take their place in unmanaged wild nature.
Scientific questions about plants themselves relate, for the most part, to questions about structure and function which broaden into concerns about environment and evolution.

Commentary & sustainability analysis

We need the most practically efficient way of addressing the future sustainability of life on planet Earth and to achieve this we need to develop a set of priorities. This discussion of plant classification might seem an extraordinarily convoluted way of expressing this but it has given us some insight into the way our minds work and how this has a bearing on both the progress of science and the way we make decisions.

Classification, as the purposive organization of taxonomic units into groups based on prioritised criteria, is an innate characteristic of sentient organisms although consciousness of the process varies in degree. Some classifications are progressive since they can be refined and improved over time, especially those that are shared by a community and can be handed on to future generations. Scientific classifications are progressive and have told us much about the physical world but to address modern problems such as that of sustainability, as a taxonomic goal, is a complex matter involving contentious taxonomic units.

Plant categories
Plants as objects of physical and spiritual significance – as foods, tools, structural materials, and medicines, but associated with this was a spiritual realm that became particularly associated with the effect of plants on the human body. Plant knowledge that went beyond the everyday, plant knowledge that connected to the spiritual world, became the preserve of a special individual, a shaman or medicine-man of some kind.

With the advent of cities much traditional knowledge was lost: knowledge of individual plants, where they grew, and their particular association with the environment and other plants and animals. Cities resulted in a completely new set of categories relating to human-created physical space where plants could be managed (cultivated) – new categories relating to gardens, parks, fields, burial grounds, markets, roads, houses, palaces and so on.

Key points

  • Classification is the ordering or grouping of objects by criteria that satisfy an end or goal.
  • Taxonomy is the study of classification, its principles, and procedures.
  • Classification begins with the pre-conscious structuring of our experience that occurs before conscious deliberation. This intuitive ordering of the world is part of the way we represent the world and part of our metaphysical intuition about the world. It is also part of our human reality, our uniquely human collective mental umwelt.
  • Biological classification of organisms arranges them by their presumed evolutionary relationships
  • One method of scientific advancement is the designation of an are of study (an academic discipline) with a community of scientists that constantly refine the categories, principles and procedures used by that study
  • We study plants through the broad range of scientific disciplines that fall under the heading of plant science (formerly the narrower discipline of botany). There is no current and widely accepted system of categories, principles and procedures for the study of the topic ‘plants and people’

Bits

Well, you might say, we study plants in all sorts of ways – we study their scientific classification, their anatomy, their ecology and physiology: we study fossil plants and garden plants, and we study the genetic code of all plants . . . and so on.

However, the question being asked here is – given today’s list of academic plant disciplines: is there a preferred way of grouping them together?

the Suppose you are the leader of a group of people studying plants, say a professor of botany at a university . . . how would you justify the selection of topics for study? No doubt you would have reasons for making your own selection. Perhaps you think that before any study of plants gets underway you need a clear picture of the objects of study – so plant taxonomy must take pride of place. Perhaps you think that our planet is under pressure from human activity, so we need to understand the role played by plants within the biosphere. In this case plant ecology takes pride of place. Maybe you just try to please all stakeholders as best you can, selecting a broad range of topics and emphasizing those of current interest to the general community – for whatever reason? This begs the question of how we arrived at today’s collection of topics that make up the study of plants.

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