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A Natural System
©2000 Gary Olsen, University of Illinois
Major Divisions of Eucarya
The Eucarya are usually classified into four kingdoms: plants, animals, fungi and protists. The first three of these correspond to phylogenetically coherent groups as well.22 However, the eukaryotic protists do not form a group, but rather are comprised of many phylogenetically disparate groups (including slime molds, multiple groups of algae, and many distinct groups of protozoa). Just as molecular analyses were required to see the natural relationships among prokaryotes, they are also allowing us to infer relationships among these non-plant, non-animal, non-fungus eukaryotes.
Many of the groups of fungi are important. In addition to providing yeast for making bread and fermenting sugar to alcohol, the fungi include the causative agents of such conditions as blight, ergot, rot, rust, smut, wilt, ringworm and athlete's foot. Although it might seem that it is straightforward to identify an organism as a fungus, this is not always the case. The unambiguous identification of the opportunistic pathogen Pneumocystis (which has not been grown in culture) as a fungus required analysis of its ribosomal RNA.
The "eukaryotic protists" also provide many organisms of clinical importance, including Crithidia, Trypanosoma, Plasmodium, Amoeba, and Giardia.
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