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Chapter 16
PLANT NAMES AND CLASSIFICATION
Systematics is the study of biological diversity and evolutionary history of organisms.
Systematics includes...
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taxonomy, the science of identifying and classifying organisms.
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phylogenetics, the study of the evolutionary history of organisms.
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nomenclature, the system used in naming organisms.
The modern system of biological classification organizes information about living things by
placing them in groups.
A international system is necessary to have clear communication among scientists
worldwide.
An international system for classifying and naming all organisms.
This system was designed to eliminate the use of common names and confusion in the
scientific world.
I. History.
The present system of nomenclature was devised by Carolus Linnaeus (Carl von Linné), a
Swedish botanist who lived in the 18th. Century.
Linnaeus published in 1753 a book called Species Plantarum, "the kinds of plants".
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He described known plants with 12 words called the polynomial name.
In Latin.
Next to the 12-word description he added a single word.
This word combined with the first word of the polynomial became the designated
name of the species.
Genus + species epithet = scientific name of the plant.
Binomial system of nomenclature.
In the classification system published in Species Plantarum any plant can be assigned to
one of 24 classes based on the number and arrangement of stamens in each flower.
Within each class the plant is then assigned to an order based on the number of pistils in
each flower.
Plants without flowers were place in a separate class.
An explanation of the Linnaean system used Species Plantarum:
http://www.rom.on.ca/biodiversity/herbaria/linnaeus.html
Linnaeus’ system of classification fell out of use in about 100 years after its publication but
the binomial system of nomenclature has remained to the present.
II. Taxonomy.
A taxonomic grouping is called a taxon.
Species may be grouped into subspecies and varieties.
Taxonomy is hierarchical: taxa are grouped into broader taxa.
Species are grouped into genera (sing. Genus).
Genera into families; families into orders; orders into classes; classes into divisions;
divisions into kingdoms.
The rules that govern the use of scientific names in botany are codified in the International
Code of Botanical Nomenclature.
Each species usually has type specimen kept in a museum or herbarium.
The type specimen serves as the basis for comparison with other specimens in determining
whether they are members of the same species or not.
http://www.bgbm.fu-berlin.de/iapt/nomenclature/code/SaintLouis/0000St.Luistitle.htm
http://plants.usda.gov/
III. The development of the kingdom concept
The separation of living things into plants and animals has probably always existed in the
mind of humans.
This division into two large groups does not work for smaller organisms and simpler
organisms.
John Hogg and Ernst Haeckel proposed a third kingdom in the 1860s. All organisms that
did not develop complex tissues were placed in a third kingdom called Protoctista.
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It included algae, fungi and sponges.
Herbert Copeland proposed 1938 the division of the Protoctista into two kingdoms:
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Kingdom Monera to include all prokaryotic unicellular organisms, e.g. bacteria
Kingdom Protoctista to include the remaining eukaryotic organisms without
complex tissues, e.g. fungi, algae and unicellular eukaryotes.
Whittaker proposed in 1969 a new scheme in which the method of nutrition was used to
separate the complex organisms:
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Photosynthesis: Kingdom Plantae
Ingestion of food: Kingdom Animalia
Absorption of food; Kingdom Fungi
Whittaker also recognized the Kingdoms Monera and Protoctista.
As technology developed and we learned more about bacteria previously unrecognized
differences appeared.
In the 1980s, Carl Woese proposed the division of the Monera into two Kingdoms, Archaea
and Bacteria, based on molecular differences found in the cell wall, plasma membrane and
RNA.
IV. Classification of major groups
Some scientists recognize a taxon above the kingdom called domain.
Your textbook recognizes three domains based on molecular evidence: cell wall structure,
RNA polymerase, initiation codon, fatty acid linkages, etc.
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Bacteria, Archaea and Eukarya.
Bacteria and Eukarya are prokaryotes.
The Eukarya includes all the eukaryotes: protists, fungi, plants and animals.
Some differences between the domains:
Cell Walls
Bacterial = peptidoglycan.
Archaeal = pseudopeptidoglycan, or protein only.
Eukaryal = plants (polysaccharide), animals (none), fungi (chitin).
Cell Membranes
Bacterial and eucaryal lipids = straight chain fatty acids linked to glycerol molecules
by ester linkages.
Archaeal lipids = branched chain hydrocarbons linked to glycerol molecules by ether
linkages - fatty acid components are not found in archeal lipids.
Initiation code.
Bacteria = formylmethionine.
Archaea and Eukarya = methionine.
RNA polymerase.
Bacterial polymerase: small single enzyme; about 4 subunits.
Archaeal polymerase: single large enzyme; 8-12 subunits.
Eukaryal polymerase: three large enzymes; 8-12 subunits.
Depending on the classification scheme there may be 12 to 30 divisions of the Kingdom
Plantae.
Families of higher plants are separated from one another by characteristics inherent in
their reproductive structures (flowers, fruit and seed). Families have primary importance in
gardening as family members generally share comparable cultural requirements and similar
insect and disease problems. Disease management and cultural techniques are often
discussed at the family level.
Genera (plural of genus) are groupings whose members have more characteristics in
common with each other than they do with other genera within the same family. Similarity of
flowers and fruits is the most widely used feature, although roots, stems, buds, and leaves
are also used.
Common names typically apply to genera. For example Acer is the genus of maples,
Fraxinus is the ash, and Juniperus is the junipers.
Species generally refer to interbreeding sub-group of genus or groupings of individual
plants that adhere to essential identification characteristics but display sufficient variation so
as not to be categorized as replicas of one another. The species name is always used in
conjunction with the genus.
V. Eukaryotic kingdoms.
1. Kingdom Protista (Protoctista)
Protists are....
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Unicellular, colonial or multicellular.
Eukaryotes.
Heterotrophs or autotrophs.
Live in watery environments.
Reproductive cycles vary but usually involve cell division and sexual reproduction.
Evolved 1.5 billion years ago
Are classified into three main categories. A polyphyletic group.
2. Kingdom Animalia
Animals are...
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Multicellular.
Eukaryotes.
Lack cell wall, plastids and photosynthetic pigments.
Nutrition is primarily ingestive with digestion in an internal cavity; absorptive in some
and others lack an internal cavity.
Tissue differentiation is complex.
Reproduction is primarily sexual.
3. Kingdom Fungi
Fungi are...
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Mostly multicellular; some unicellular.
Nonmotile filamentous eukaryotes.
Heterotrophs.
Lack plastids.
Absorb nutrients after extracellular digestion.
Reproductive cycle usually involve sexual and asexual stages and can be complex.
4. Kingdom Plantae.
Plants are...
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Multicellular.
Eukaryotes.
Autotrophs; a few species have become heterotrophs.
Cell wall, plastids and photosynthetic pigments.
Alternation of generations.
The following diagram has been taken from http://www.plantkingdom.com/index.htm
http://theseedsite.co.uk/class.html
http://theseedsite.co.uk/class2.html
http://theseedsite.co.uk/families.html