The history of taxonomy of plants
Taxonomy is the science of classification. The aim of biological taxonomy is to name,
describe and classify all organisms.
The history of plant taxonomy starts with the ancient Greeks. Theophrastus, a student of
Aristotle, wrote his famous book ‘Historia Plantarum’ around 300 BC. This is the oldest
known botanical encyclopaedia, in which plants are classified in different categories based on
easily visible characters. This classification has been in use for more than 1000 years.
In the 16th century the interest in botany is revived by Otto Brunfels, Hieronymus Bock and
Leonhart Fuchs. According to Linnaeus they are the ‘fathers of botany’. They described live
plants, classified them and published their work so that it became widely available.
Rembert Dodoens wrote the Dutch ‘Cruydeboeck’ in 1554, in which he divided the Plant
Kingdom in six groups. He mainly focused on useful plants. Carolus Clusius, founder and
first prefect of the Hortus botanicus Leiden, was a botanist and a plant collector. In the period
at the end of his life, in which he lived in Leiden, he published his vast knowledge in
‘Rariorum Plantarum Historia’ (1601) and ‘Exoticorum Libri Decem’ (1605).
In 1753 Linnaeus published ‘Species Plantarum’, one of the most important books in the
history of botany. Here Linnaeus introduced binomial naming of species; each name
consisting of a genus and species name. ‘Species Plantarum’ includes a complete list of all
plant species known at the time, classified on the number and position of male and female
reproductive organs. Linnaeus is regarded as the father of modern naming.
The evolution theory as published in ‘The Origin of Species’ in 1859 by Charles Darwin
caused a revolution in biology. Evolution is a slow process of change in everything alive.
From the beginning of life itself organisms have been passing beneficial adaptations on to
their offspring. Usually hereditary material gets transferred to the next generation without
change, but sometimes changes in the genes and chromosomes do occur, which is called
mutation. Variation in a population is caused by mutations and new combinations of genes in
offspring (recombination). Some of these recombinations and mutations may enable the
organisms to survive and breed more effectively their environment. Because of natural
selection the organisms with the genes providing the best adaptations to the environment will
produce a larger number of offspring.
Evolution occurs because of the interaction of mutations and natural selection. The basic idea
of evolution was gradually developed in the works of Buffon, Lamarck en Cuvier (among
others), but Charles Darwin was the first to present a convincing evolutionary theory.
The evolutionary theory had a huge impact on taxonomy. It has always been possible to
classify plants using one or several characters, for example trees or herbs, or flower colour.
Such a classification is practical and easy to create, but does not give a proper representation
of the genetic relationships between plants. This is considered to be an unnatural
classification.
Generally taxonomists try to construct a natural classification based on the evolution theory,
in which relationships are derived from the history of development of the taxa. They attempt
to reconstruct this developmental history by using as many characters as possible.
In the course of the history of taxonomy, many different approaches have been used to
construct a natural classification. They depend on the availability of ever more advanced
techniques of observation, theoretical insights in the evolutionary process, and different
methods of data analysis. Relationships are visualised in a diagram representing the Tree of
Life, in which the direct descendants of a common ancestor are closest together; such a tree is
called a cladogram.
More plant characters could be compared with the use of modern techniques, for example
(electron)-microscopy to observe details of anatomy and morphology, and different
techniques in chemistry for the detection of so-called secondary substances. The discovery of
techniques to quickly read the characters present in the DNA and RNA (the genetic material
in a cell) enables the reconstruction of relationships in much more detail. The development of
fast computer programs to analyse large amounts of characters in order to create cladograms,
led to the first cladogram of the ‘Angiosperm Phylogeny Group’ (APG I) in 1998. A second,
more detailed cladogram plus classification, APG II, followed in 2003. This has been used for
the classification in the 23rd edition of the ‘Heukels’ Flora van Nederland’ (flora of the
Netherlands), with some more recent modifications. This classification is still subject to
changes, mostly due to the discovery of ever more characters in a growing number of species.
Some of the most recent discoveries have been used to arrange the plants in the current
systematic garden.