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Classification

Charles J. O'Kelly okellyc at ayers.BCH.UMontreal.CA
Mon Mar 20 19:43:16 EST 1995


In article <9503171444.AA01905 at newpisgah.keene.edu> kbergman at keene.edu
 (Kenneth D. Bergman) writes:

> The Five Kingdom scheme is employed in most introductory Biology 
> textbooks in the U.S., including those by Neil Campbell, 
> (botanist) Peter Raven & George Johnson, and Cecie Starr & Ralph 
> Taggart. 

which is a pity ... more by default than anything else.

> The assignment of [Chlorophyta] to Kingdom Protista rather than Plantae
> probably reflects the judgement that taxonomy ought to reflect more 
> than simple continuity of lineage

not really.  as I understand "five kingdoms", the eukaryotic taxa
Animalia and Plantae are defined on the basis of their principal
"synapomorphy", the formation of embryos.  Fungi are hyphal.  
Anything without animal embryos, plant embryos or fungal hyphae 
cannot be placed in these kingdoms, by definition, and therefore
lands in the "trash basket", the Protista.  

thus, on the basis of an essentially arbitrary (though easily
conveyed to students) set of distinctions, green algae are excluded 
from Plantae, choanoflagellates are excluded from Animalia, and 
Chytridiomycota are excluded from Fungi, despite the growing body of 
morphological and molecular evidence indicating that these "protists" 
belong to these clades. 

I do not think these definitions of convenience persist because of
a desire to devalue or hide the phylogenetic relationships among
protists.  indeed, to hide phylogenetic relationships in the 
classification of animals, plants and fungi is simply not allowed
among practicing taxonomists.  they persist because, unlike for the
plants, animals and fungi there is no clear understanding, let alone a
clear statement, of what the phylogenetic relationships are among
protists, and because, in the interim, "five kingdoms" presents a
clear, easily memorized and (for non-protist eukaryotes) essentially
accurate classification.

my own prejudice is that a modern classification, that includes
factors other than lineage, must develop from an understanding of
the underlying phylogeny, not being developed in ignorance of that
phylogeny.  I think that anything less is a disservice to science
and the students of science.

especially given our growing realization that Animals, Plants and
Fungi are three sister taxa, and most protists (read "most eukaryotes")
fall into two or more major lineages that include none of the 
"big three".

yes there are communities of people who study "protists" regardless
of their phylogenetic affinities.  there are also people who study
"trees" (for example) regardless of their phylogenetic affinities.
in the latter case, however, the practitioners at least have a 
basic knowledge of the underlying phylogeny, and when it does (and
does not) impact on other matters of "tree" interest.  I look forward
to the day when students of protistology have the same basic
understanding. 

> and most new students of Biology (including
> future phycologists)in the U.S. are now routinely exposed to this 
> taxonomic treatment.

I hope they are also exposed to its flaws, as revealed by current
research on protist systematics.


charley o'kelly
mad protistologist
okellyc at bch.umontreal.ca
okellycj at nh.ngs.net





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