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Taxonomic steps1 (20-Mar-03)


Out in the woods we have discovered species A-F and have had different ideas about how to classify them. A is a circumboreal species, while B-E are known only from the Himalayas and adjacent mountain ranges in southeastern China and Vietnam. E is known only from the type collection, although it has been described under two different names. F is only discovered when you investigate the genus to which these species belong in the mountains of Taiwan. This is how this section of the genus appears to us. Run your mouse over the image to see how it might look in the eyes of an omniscient deity.

This graphic is meant to suggest the problem that taxonomists encounter when they set out to do the taxonomy of a group. The organisms they seek to study appear as if they could be classified in a number of different ways, even though they have only a single true set of historical relationships. How then does a taxonomist proceed in order to arrive at a classification that reflects as much as possible that single truth?


Steps in a taxonomic study

  1. Circumscription of the study group
    Note the importance of casting one's net wider than the immediate group of know group members, so as to ensure that one includes all of the "real" group (cf. species F in the example above).

  2. Choice of representatives for the study group

  3. Choice of characters and their states, if appropriate
    To be useful, characters should vary most between entities in the study group, and least within those entities. The following issues are also worth considering:

  4. Analysis of character variation
    This will be discussed in subsequent lectures.

  5. Assessment of relationships

  6. Construct hierarchy of relationships

  7. Construct classification

  8. Put together the practical apparatus (monograph; descriptions, keys)


Different approaches to a taxonomic study

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Sources

Davis, P. H. & V. H. Heywood (1965). Principles of Angiosperm Taxonomy. Edinburgh, Oliver & Boyd.

A lecture by Prof. J. E. Eckenwalder in March 1992, and an ongoing collaboration with Prof. S. P. Vander Kloet (Acadia University).


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Please send your comments to tim.dickinson@utoronto.ca; last updated 23-Mar-2003