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Classification and Systematics (Levels of Taxonomic Categories (Species…
Classification and Systematics
Concepts
Approx. 400 million years ago mutations and natural selection gave rise
Since then the evolutionary line has progressed and changed
Phylogeny
The hereditary relationships of any group of organisms
Basically the evolutionary history of each member of the group
The goal of modern systematics
To understand each evolutionary lines
Nomenclature's
Reflect their relationships accurately
In the past plants were given names merely so people could communicate about the various uses and types
Taxonomists were to discover, identify, and give unique names to the new species
They realized a valid system of assigning names to species would be one that reflected evolutionary relationships
In the 19th century, taxonomists adopted the goals of developing a natural system of classification
Levels of Taxonomic Categories
Species
The most fundamental level of classification
A set of individuals closely related by descent from a common ancestor
Word is both singular and plural
Subspecies
If a species can't interbreed well
Genera
Closely related species related by a common ancestor
Deciding if several species are related is difficult
Are natural
Monophyletic
Polyphyletic group
Unnatural
Evolved from different ancestors
Family
Composed of one or many genera
Most are well defined
The levels above family
Order
Class
Division
Kingdom
Names must have a certain ending to indicate the classification level
Except for kingdom, genus, and species
Species epithet
Distinguishes species from the other species of the genus
Cladistics
A method of analyzing these phylogenetic evolutionary relationships
Studies are complicated by the fact that plants can resemble each other for two distinct reasons
Have descended from common ancestors
Have undergone convergent evolution
Synapomorphies
Features similar to each other because they have descended from a common ancestral feature
Homoplasies
Natural selection may favor mutations in each line that results in similar phenotypes
Should never be used to conclude that plants are closely related
Taxonomists study every aspect of plants using a variety of tools
Electron microscopy
Light and transmission electron microscopy
DNA sequencing
Understanding Cladograms
Cladogram
A diagram that shows evolutionary patterns by means of a series of branches
Node
Point at which a cladogram branches
Represents the divergence of one taxon into two
Common ancestor
Clade
Any ancestor and all of the branches that lead from it constitute this
Unsolved polychotomy
Not enough data, and then various species are shown arising from the same node
Are hypotheses
parsimony
Prefer the simplest possible hypothesis
When a computer program makes a caldogram
Equally parsimonious
Artificial classification system
Fundamental classification system
Several key characters are chosen as the basis of classification
Usually have the goal of easy plant identification
Form genera
