The Early Years of Plant Taxonomy
Kevin Shade
Introduction
In the mid part of 2011 there were a series of interesting and informative television programmes
about botany, entitled “Botany: A Blooming History”. One of these programmes covered some of
the early pioneering work on plant taxonomy (the naming and classification of plants). The
following notes are largely based on the content of this programme.
In the late 17th century the new discipline of botany was thinking about plants in new ways. What
botanists were looking for, and are still looking for, is how the plant world fits together,
understanding what is related to what. Classification is about revealing the natural order of the
world and the classification of plants is the basis of the science of botany. Pioneering botanists
struggled to invent a system for classifying and naming plants.
John Ray
The first breakthrough in the classification of plants was made by John Ray in the 17th century in
Cambridge, a person considered by some to be one of the greatest ever naturalists. He detected,
for the first time, a natural order. His pioneering work on classification moved the study of plants
away from superstition and towards science. He collected and pressed plants and observed them,
the more he looked the more he began to detect a pattern emerging in the plants he collected. This
pattern would be his first discovery. He recognised variation (e.g. differences in size, flower
colour etc.), differences that some people would have considered to represent fundamental
differences. He considered these variations to be recognised differences in plants from seeds of
the same plant, in the same way that children may have different eye colour or other
characteristics compared to their parents. He recognised that this variation didn’t mean that the
plants belonged to different species but was indicative of natural variation among plants. He
realised that there is a set of characters that remain unique to a group of plants, and in particular
the flowers, and inside these the seeds, seed vessels and the outer parts of the flower, the sepals.
These were characteristics that didn’t vary within a given species and consequently these were
things that could be used to define a species. Before Ray no one knew what a species was, or how
to identify one (there is, however, still no universally accepted definition of a species). For the
first time there seemed a clear way of defining a species. This was a huge step forward and was
one of Ray’s major contributions in botany. Soon after, he was kicked out of Cambridge
University because he refused to swear allegiance to King Charles II. He left Cambridge and
rented a room owned by one of his students.
He had defined a species by those characteristics of plants that didn’t change, now he wanted to
go further, to see if species themselves can be organised and grouped. He saw things that others
missed. He turned his attention to looking at seeds which, when cut open, he discovered that
some split easily in two, others did not. He uncovered a fundamental difference in the plant
world, those that split easily into two he named dicots and the others monocots. As he looked at
the overall structure of plants in these two groups he found five more significant differences;
differences in the flowers, stems, roots, first leaves to emerge and mature leaves. He realised that
any further advances in classification could only come about by looking at the whole plant (i.e.
all its features). He created order out of chaos and his principles of plant classification were still
used 350 years later. The principles of classification developed by John Ray in the 17 th century
were largely ignored at the time. He got the science right but failed to communicate his ideas
effectively.
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Carl Linnaeus
Carl Linnaeus (botany’s first ‘celebrity’) began his career in Uppsala in Sweden. He used a
different approach to that of Ray. He became an expert in plant anatomy and discovered that
plants had different numbers of sexual parts. Some had two male parts (stamens) and one female
part (pistils). Others had different ratios of male to female parts. He considered that he had found
a way to classify the plant kingdom. He argued that nothing could be more fundamental to a
plant’s identity than its sexual parts. He believed he could order the vast diversity of plants by
their sexual parts alone. In 1735 he published “Systema Naturae”, a book that changed the
botanical world. His classification system was based on the numbers of stamens and the numbers
of pistils. His book caused uproar, not because of his bold ideas, but because of the language he
used to express them as people were offended by the sexual connotations. He travelled to
England to get his ideas accepted.
Phillip Miller
He met Phillip Miller, at the time the greatest horticultural authority in Europe (someone who
started his career as a florist in the flower markets of London) who received plants from around
the world. One of the great difficulties at the time concerned plant names, with different
countries, different regions and at times different gardens using different names. As there were no
universally agreed names it was impossible to communicate effectively. Advice and growing tips,
for instance, could not easily be shared when people didn’t know if they were talking about the
same plant. Miller devised a system of regulating the naming of plants. To do this he founded the
Society of Gardeners and meetings were held to discuss the names of flowers, trees and shrubs
that were flooding in from the New World. The society attempted to compare plants from abroad
and those already established in English gardens and to discover where the real differences, if
any, lay. The society eventually collapsed, overwhelmed by the enormity of the task. However,
this work made his name and he was appointed head of the most prestigious botanic garden in
London, the Chelsea Physic Garden (founded by the Worshipful Society of Apothecaries of
London in 1673 for its apprentices to study the medicinal qualities of plants). Miller transformed
the garden and was responsible for doubling the number of foreign species successfully grown in
Britain. He went further and developed a centre of economic botany (e.g., growing cotton and
roots used in the dye industry etc.). For exotic plants he introduced glasshouses with coal fired
heating systems. In his day he was regarded as the most distinguished and influential gardener in
Britain, not just because of his achievements at the Chelsea Physic Garden but also because of
what he had written. He took all the notes from the ill-fated Society of Gardeners and compiled
the first comprehensive dictionary of gardening, which was published in 1731. He listed plants in
alphabetical order and made an attempt at classification. This became the standard reference
work for gardeners around the world. All the names given to the same plant were listed together,
eliminating some of the confusion that was prevalent. This publication gained more credence and
authority with every new edition and turned Miller into a superstar of the botanical world. His
dictionary brought together all that was known about plants, it brought order and focus for all
knowledge available at the time. It was this dictionary that brought Carl Linnaeus to the Chelsea
Physic Garden in 1736. Linnaeus wanted Miller to promote the system of sexual classification by
including it in the next addition of the dictionary. However, Miller dismissed the classification
proposed by Linnaeus.
Carl Linnaeus
Linnaeus went to the Oxford Botanical garden to see John Jacob Delenius, Professor of Botany.
The two became firm friends. Linnaeus returned to Sweden and established a new national
botanic garden at Upsalla. This was laid out according to his sexual system of classification (the
garden is still laid out this way today). Plants were laid out according to the number of sexual
parts they possess. He subsequently became Professor of Botany at the University and Director of
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the Botanical Garden. Linnaeus identified a significant weakness with botany at that time; the
names of plants were unwieldy. For example;
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Trifolium orientale altissimum caule fistulosa flore albo was a type of clover.
Viola floribus radicalibus corollatis ortientibus caulinis apettalis seminiferis was a viola
(this name translates to short stemmed, free-petalled, fruiting violet).
These names consisted of detailed descriptions of the plants but were very unwieldy and
impractical. Linnaeus set out to find a neat and easy way of naming plants. He realised that all a
plant name needed to do was to designate it; it did not need to describe it. A universal language
was needed to do this and that is what Linnaeus gave us. He reduced the plant names to just two
words. Thus Viola floribus radicalibus corollatis ortientibus caulinis apettalis seminiferis
became Viola mirabilis. This gave us a simple, elegant system that was much easier to use. Over
the next two decades he applied the two-name system to 7700 plants, which were published in the
next best seller “Species Plantarum” (published in 1753 in two volumes). It was a huge step
forward for science and Linnaeus became the authority on what names plants should be called. In
the final addition of Miller’s dictionary (the 8th edition), the binomial system developed by
Linnaeus was included. This binomial system was a colossal contribution to science and is his
abiding legacy. The binomial system of nomenclature is used in all branches of biology (plants,
animals, fungi, bacteria etc.). Thanks to Linnaeus botanists around the world could identify and
classify plants, teach, correspond and advance their science easily, efficiently and coherently.
This naming method was successful and survives to this day. But the more botanists looked at his
system of classification the more flawed it appeared as there were inconsistencies and anomalies.
For instance, lilies, yuccas, witches broom and asparagus all had 6 male and 3 female parts but
these plants look totally different. In addition the number of male and female parts can vary
among different flowers on the same plant. This was not a reliable way to group plants. The
mistake that Linnaeus made was to focus on one factor, the sexual organs of plants. As this
system fell into disrepute botanists began to rediscover the work of the long forgotten John Ray.
Among them was Philip Miller who had the last laugh against his great rival, Carl Linnaeus. The
Chelsea Physic Garden never embraced the sexual system of classification promoted by
Linnaeus.
Thomas Fairchild
The power of religious authority became a block on scientific advance. In 1716 Thomas Fairchild
(a successful nurseryman) carried out experiments never done before. He wanted to create an
entirely new flower, so he could sell blooms that his rivals didn’t have. He created an artificial
hybrid flower, a plant that couldn’t be found in nature. He prepared two flowers, a carnation and
a Sweet William and took the male pollen from the Sweet William and placed it on the female
parts of the carnation. He waited until the carnation produced seeds then sowed them. He tried to
preserve them by cutting the stem of the pink bloom and pressed them between two sheets of
paper (this was a specimen of the first scientifically created hybrid). He was concerned about the
influence of the church because it cast doubt on the story of creation (where God created all
plants and animals). Thomas Fairchild thought he had created a new species. To assuage his guilt
he made a benefaction to a church in Shoreditch so an annual sermon could be preached to
glorify the work of creation. He knew how important his discovery was, he had made a new plant
and that should not have been possible. He knew man’s relationship with plants would never be
the same again. It was nearly 4 years before he dared to tell the world about his experiment. On
the 4th February 1720 he went to the headquarters of the Royal Society in London (the foremost
scientific institution) and presented his pressed flower to the great and the good of the scientific
world, fearful of the reaction he might receive. The members of the Royal Society realised its
significance and were excited by the possibilities the hybrid presented. However, Fairchild’s
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hybrid could not produce seeds, it was sterile, and no one knew why. What was missing was the
piece of the jigsaw that would enable plant scientists to create fertile hybrids for better plants,
stronger crops and more efficient medicines, for instance. The missing link was an understanding
of how different plant species evolved. The missing link arrived in the shape of Charles Darwin
and his book on the origin of species. He demonstrated that plants had the ability to adapt to their
surroundings and as a result increase their chances of survival.
Charles Darwin
Charles Darwin set out on his epic journey on HMS Beagle in 1831. He was fascinated (amongst
other things) by the diversity of plant life found in the southern hemisphere. He noticed that those
plants pollinated by wind had little colour whilst those that needed to attract insects were brightly
coloured. He realised that natural selection applied as much to plants as it did to animals. His
theory of evolution was finally published in 1859 (delayed for a long time because of his fear,
like that of Thomas Fairchild, that his findings would result in criticism and condemnation).
Whilst it may have put the cat among the pigeons in Victorian religious circles, for biologists it
was like finding the Holy Grail because it explained everything. The 19th century botanists
recognised the significance of Darwin’s work on how and why plants evolve into different
groups. In his notes for the book Darwin used an illustration, a metaphor of a tree showing how
species diverged as they evolved. Growing from a central trunk it showed some branches dying
out and others sprouting further growth. The newest twigs and leaves far away from the roots but
still connected. Darwin showed why we could classify plants; those in a natural well-defined
group share a common ancestor. He explained why plants with fewer things in common were
more distantly related and why plants that have a lot in common are more likely to produce fertile
offspring (the role that genes play were not known in Darwin’s time. So while he was able to
deduce how things evolved he was not aware of the underlying mechanism behind it, we had to
wait until well into the 20th century and the discovery of the role that DNA plays before this
became apparent). The plants that Fairchild used, the carnation and Sweet William, came from
two distinct species. They were not closely related enough to breed successfully.
Conclusion
The understanding of the importance of classification underpins all botanical science to this day.
Many different systems of classification of plants have been proposed. These are generally
recognizable as being of the three following types:
I. Artificial systems: organisms classified according to one or a few characters, primarily for
identification purposes. Interrelationships and evolutionary trends may not be taken into
consideration.
II. Natural systems: reflect the situation, as it is believed to exist in nature, and utilize all
information available at one time. Thus natural systems may vary considerably from one period
to the other.
III. Phylogenetic systems: organisms classified according to their evolutionary history. It reflects
genetic relationships between the different groups.
It is now considered by taxonomists that classification (whether for plants, animals, or
microorganisms) should reflect the evolutionary process that produced them. Variations in DNA
reflects differences in the genetic make-up of the plant and these variations link species, genera,
families etc. into a shared network of descent. The modern methods of classification, therefore,
use analysis of DNA as the basis of classification. The principles underlying this approach will be
covered in a subsequent article.
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