Classification and Systematics
• Nomenclature – the first system of naming of organisms
for communication purposes
• With the an understanding of evolution and natural
selection taxonomists felt that a naming system should
reflect evolutionary relationships – goals of such a
system
– A natural system whereby the system grouped closely related
organisms together – greater pressure was placed upon the
taxonomist
– Names were based upon evolutionary relatedness
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Types of Classification Systems
• Artificial Systems – the use of several key characters
used to simply get to the identification of an organism
• Natural Systems – trace the phylogeny of an organism –
their use has grown since more and more information is
know about the organisms being classified
– Physiological information
– DNA
– Still missing pieces
• For fossil organisms, frequently a blending of the two is
used so that we can identify an unknown fossil but also
group it with closely related fossils
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Historical Aspects of Plant Classification
• The Ancient Period
– Theophrastus of Eresus
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Student of Aristotle
4th century B.C.
Based upon leaf shapes and whether they were trees, herbs or shrubs
Differentiated between flowering and nonflowering plants
Identified sexuality in plants, realizing fruits developed from carpels
– Pliny the Elder (23- 79 A.D.)
• Natural historian
• Published Natural History – attempted to describe everything in the world,
even included mythological creatures
• Was the authoritative work for over 1,000 years
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Historical Aspects of Plant Classification
– Dioscorides
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Greek physician
1st century AD
Published Materia Medica
Classification based upon medical uses and lasted for over 1500 years
– Herbals and the Doctrine of Signatures
• Herbals – describe the medial uses of plants, including much folk lore
• Signature of Doctrines – the morphology of the part of the plant that was
used related to the part of the body the plant part worked on (walnuts
[brains] hepatica leaves [liver])
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Historical Aspects of Plant Classification
• Renaissance Period – expanded with the advent of exploration –
many earlier works were proved to be wrong or have inaccuracies –
as the number of organisms grew it became apparent that a
consistent system to name organisms was needed
– Bauhin
• Swiss botanist
• 15th century
• Took advantage of exploration and expeditions
• Classified over 6,000 plants based upon observable characters
• Used a double Latin name, 100 years before Linnaeus and was the first to
establish the concept of a genus
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Historical Aspects of Plant Classification
– Carolus Linnaeus
• Swedish
• 1753 published 2 volume work, Species Plantarium (Species of the
World)
• Developed the binomial system of nomenclature
– Gave each species a two part name, binomial system
– First word in the genus is capitalized
– First and second words constitute the species name; second name is
usually lower case and both are underlined or in italics
– This method of classification was an artificial one, based upon a few
reproductive features and did not always represent true relationships
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Historical Aspects of Plant Classification
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The Modern Period: Evolution and Classification
– Lamarck
– Darwin/Wallace (1859)
• Both proposed the concept of natural selection
• Gave rise to natural systems of classification
– Engler and Prantl – turn of the 20th century (1915)
• First to develop a phylogenetic system that became widely used
• Published Die Natürlichen Pflanzenfamilien
• Used floral parts (no petals most primitive, monocots more primitive than dicots
– Bessey – early 1900’s
• Used Magnolia flowers (many parts, spirally arranged as being most primitive) – many
of his ideas are still used today
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Levels of Taxonomic Categories
• Species the most basic unit – definition is variable; at times
subspecies are used (mention problem of lumpers vs. splitters)
Genus
Family
Order
Class
Division
Kingdom
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Levels of Taxonomic Categories
• Cladistics – widely used in evolutionary studies – use the
fact that at some point in time a given organisms evolves
a character or characters different from its parent
producing two groups, one with the original character
and a second with the new, derived, character
(represented by a fork in the tree)
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Levels of Taxonomic Categories
– Terminology
• Plesiomorphies – characters present in a group’s ancestors, relictual or
primitive
• Symplesiomorphies – primitive characters shared by two or more groups
(shared traits)
• Apomorphies – derived characters, not present in ancestors
• Synapomorphies – shared derived characters, found in two or more modern
groups
• Autoapomorphies – when a derived character is found in only one group
(ears of corn as a grass)
• Homoplasies – the result of convergent evolution – appear the same but not
evolved from the same evolutionary trait
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Types of Evidence Used for Taxanomic Analysis
• Homology and Analogy
– Homologous Features (Synapomorphies) – those that have been
derived from a common ancestor – ex. Members of the
anthrurium family all possess a spathe and spadix inflorescence
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Types of Evidence Used for Taxonomic Analysis
– Analogous Features (Homoplasies) – result from convergent
evolution – ex. Cacti and Euphorbias (both succulent with
spines; not closely related)
Determining what is homologous or analogous is most
difficult, especially if a small genetic change results in a
gross phenotypical differences
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Taxonomic Studies
• Exploration and Discovery
– Very slow process, takes time, money, and dedication
– Results in
• Finding new individuals that must be classified
• Studies multiple specimens needed to understand individual
variability of a species
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Taxonomic Studies
• Preliminary Studies of New Plants
– Using keys specimen must be identified – can be easy to very
difficult
– If it can’t be identified it is then sent to a specialist in the area
and in some cases is deemed a new species and named
• International Code of Botanical Nomenclature
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A unique binomial name must be assigned to it
Plant must be described in numerous languages
Name must be published in a peer reviewed journal
Location of type specimen must be made evident
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Taxonomic Studies
• Biosystematic and Experimental Studies
– Initially a new species is classified based upon current
knowledge of the plant
– The same can be true of previously established species as new
techniques arise
– If one were to use these techniques on all specimens this would
take a huge amount of time
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Major Lines of Evolution
• Five Kingdoms
– Monera (bacteria and cyanobacteria)
– Protista (algae and protozoans)
– Myceteae (fungi)
– Animalia (animals)
– Plantae (plants)
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Major Lines of Evolution
• Life began approximately 3.5 billion ya
– First Organisms
• Unicellular
• Cell membrane, cytoplasm, DNA, and no membrane bound
organelles
• Grouped in the Monera
• Photosynthesis (chlorophyll a) evolved in this group, produced an
oxygen rich atmosphere
– Second Advance
• Membrane bound organelles (mitochondria; endosymbiosis)
• Living organisms similar to these in the Protista
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Major Lines of Evolution
– Third Advance
• Cell wall of chitin
• Grouped in the fungi
– Fourth Advance
• Multicellular organisms
• Distinct tissues
• Highly differentiated cells
– Fifth Advance
• Another endosymbiotic relationship; this time with a cyanobacterium,
became a chloroplast
• Occurred about 400 million ya
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