Paraphyly and names
skala at INCOMA.CZ
Thu Jan 31 09:34:42 CST 2002
From: SKÁLA Zdenek
>>...Very often one need to have a *system* of taxa instead of to discuss one
>>particular clade. Such cases include (but are not restricted to) teaching
>of biology in a school, arrangment of national faunas/floras etc.
>Why? Cladistic taxa form a system. What is the problem? There is nothing
>wrong with teaching a course about mammals (a recognized monophyletic
>group), or organizing that course around the traditionally recognized
>subtaxa - such as the "orders", so long as one uses monophyletic groups.
Imagine - as an example - an arrangement of taxa in a national flora. You will want some higher taxa to sort species reasonably (sorting alphabetically by specific epitheta has several disadvantages). Now we have your proposal that either cladogram or ad hoc/traditionally selected taxa will suffice.
(1) Cladogram does not provide a basis for sorting (unless it is fully pectinate which is a rare case when we deal with many species).
(2) Traditional/ad hoc taxa: many traditional taxa are paraphyletic or even polyphyletic (Sympetalae etc.); you will of course exclude them. Then, you will have some mono(holo)phyletic higher taxa and some species that are not classified within higher taxa. How will you arrange this stuff? Will you simply create sister taxa to those that are "traditional"? And what about basal clades? Will you simply re-arrange the system in order to retain the traditional groups? Progress in the cladogenesis reconstruction will probably show that many traditional taxa are either nonmonophyletic or weakly supported. And what about your ad-hoc taxa? How will you select them and why just those and not some others? If you are happy with the cladogram only, OK; however your approach do not lead to a stable nor to an informative *system of taxa*.
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