In 2007 we celebrate the 300th anniversary of the birth of Linnaeus,
the eighteenth century Swedish physician best known for developing a
pragmatic approach to naming the basic units of biological
diversity. Linnaeus leaned heavily on the work of earlier scientists,
but he was relentless in applying his new binomial approach across the
whole of biology, and to material brought back from all over the
world. This great work of synthesis, and its near comprehensive
systematisation of the diversity of life as it was known at the time,
established Linnaeus as one of the great scientists of his day. It
also set new standards and was of great practical value. It became an
essential tool in organising the explosion of knowledge that resulted
from rapid exploration of the natural world through the late
eighteenth and nineteenth centuries. In this sense, Linnaeus made
possible the insights of Darwin and Wallace. Linnaeus' approach to
recognizing and circumscribing the basic units of diversity, which he
then named, was comparative. It was also based on examination of
reference specimens. But it was nevertheless largely intuitive and
resulted in a concept of species identity that was fixed. It is
remarkable that despite current knowledge of how species develop
through the processes of evolution, despite ever deeper insights
gleaned from genetics, and despite advances in the theory of
systematics, the approach employed by Linnaeus and other naturalists
of the eighteenth and nineteenth centuries persists and remains
central to much of our modern understanding of biological
diversity. In part this is because their work has stood the test of
time: we now know that many of the species that they recognized do
have a meaningful biological identity. But the seemingly sparse
application of more sophisticated techniques to circumscribing species
in Nature also undoubtedly reflects the daunting practicalities:
outside the most conspicuous groups of animals the variety of life is
vast, poorly sampled and very imperfectly understood. For the
specialist the unevenness in our current concepts of species identity
represents a challenge, and fertile ground for developing deeper
understanding. But in other areas such unevenness is inconvenient. For
example, we depend on reliable notions of species identity to help set
policy for the conservation and sustainable use of natural
resources. Instability can be uncomfortable and can have political and
economic ramifications. Legislation designed to regulate the
conservation and use of species, for example the Convention on
International Trade in Endangered Species, or similar efforts at the
national level, all rest on the presumption that the relevant species
can be reliably and unambiguously identified. Beyond these practical
issues the fundamental nature of species remains controversial. Many
of these lively arguments revolve around matters relating to different
notions of species identity, including how species recognize each
other, and how they are recognized by us. Another controversy is over
the rules by which species are named: an area of debate confounded by
an unfortunate weakness inherent in Linnaean binomial
nomenclature. Uniform application of the binomial approach requires
uniform concepts of both genus and species identity. The binomial
system, rather unfortunately, intertwines the delivery of
straightforward species labels, with the much trickier issue of how
similarities and differences translate into hypotheses of evolutionary
relatedness at the generic level. The focus of this lecture will be on
concepts of species identity in plants. The examples will illustrate
the heterogeneous state of current knowledge. Many economically
important or biologically interesting plants have been well studied
and provide insights into the identity of some plant species in
genetic and evolutionary terms. But at the other end of the spectrum
many plant species (perhaps the majority) are not well
understood. Their identity rests on a preliminary interpretation of
similarities and differences in plant form, that remain to be
understood in terms of the biological processes that created them.
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