Dichotomous Key

This e-book can help with the identification of unknown organisms. The method adopted uses mostly a dichotomous key based on two choices, which is either in written format or pictographic, or both. For convenience, there may be polytomous sections within the book.

A written dichotomous key presents the reader with two statements that describe certain characteristics. The statements should be mutually exclusive for the key to work efficiently. For example, 'it is either red or it isn't'. On selecting one, the reader is presented with the next couplet choice in the key and so on - to eventually arrive at an identification. This key uses hyperlinks to navigate.

Classification with keys

Taxonomic systems are based on similar characteristics or increasingly on DNA analysis. The systems attempt to model the natural order, thus helping research by classifying different organisms. Taxonomic systems vary, but the following system has been found useful:

Domain
Kingdom
Phylum(called Division in plant
Class
Order
Family
Genus
Species

There are many sub units in use.

Keys usually start with a first selection from the following:

Plantae - Plants. Typically multicellular, sessile organisms. Their cells have walls composed of cellulose. They are autotrophs, and photosynthesize (with exceptions).
Animalia- Animals. Typically multicellilar, motile organisms. They lack rigid cell walls and are heterotrophic (with exceptions).
Protista - (A contested group of around 40 phyla of eukaryotic organisms) Typically simple, eukaryotic unicellular microorganisms or multicellular microorganisms without specialized tissues.
Fungi - Include yeast and molds. Typically eukaryotic, multicellular organisms. Like plants, they are sessile, but unlike plants they lack chloroplasts and are heterotrophic (with exceptions).
Bacteria - Ubiquitous, single-celled prokaryotes a few microns in size, with varying morphology.
Archaea - Relatively small group of single-celled prokaryotes more closely related to the eukaryotes then to the bacteria.

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Limitations of a dichotomous key

If the organism is included in this key - it would be found and this volume remains a finished work. Whilst dichotomous keys have proved useful, they often offer dilemmas due to individual variations, so with any dichotomous key it helps to have two or three examples to improve sorting. Keys are useful but tend to become increasingly cumbersome as the lower levels are reached especially at genus level and below.

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How the key works

Go to start
Use choices given to arrive at the lowest possible level
Organism is identified as much as possible

If the description at each level does not appear accurate then back up to some earlier couplet and start over, questioning each decision more carefully. Finally, a verification step is important by comparing the specimen with any further details available including description,photographs and other reference. The habitat and location where the sample was collected is useful for plants. If the description and other information satisfactorily confer, then a correct identification is possible.

The keys in Wikibooks are still under development.

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