Well, actually in modern systematics polyphyletic groups (once recognised
as such) should not be accepted, whatever their rank (subgenus, family,
order or phylum). In this framework (that one can also refute), a taxon
above the species level is a group that include ONLY and ALL the taxa at
the subordinate level descending from the same ancestor: thus it is
monophyletic (ONLY) and holophyletic (ALL), in strict terms.
This is not only speculations of phylosophers of Science, but in its spirit
would provide a univocal way of constructing classification. Admittedly,
there is no universal concordance on the topic, but I guess it can be said
there is a general convergence on the need that a modern Natural
Classification would be made of monophyletic taxa.
Thus, it does not really depends onwhich group one takes. Polyphyly arises
when species descending from different ancestor are put under the same
subgenus: they can be three, four or one thousand, for "too many" is not a
phylogenetic standard.



At 21.14 28/08/00 +0200, you wrote:
>Well, it depends which group you take. Polyphyly usually arises when too
>many species arr put under one genus, I guess that my definition of Erosaria
>assembles a polyphyletic group, but in subgenera you usually have only two
>or three species, and polyphyly is at very low rank then.
>
>Sincerely
>Felix
>--
>
>
>> Von: "Maurizio A. Perini" <[log in to unmask]>
>> Antworten an: Conchologists of America List <[log in to unmask]>
>> Datum: Mon, 28 Aug 2000 19:23:07 +0200
>> An: [log in to unmask]
>> Betreff: R: A systematics question
>>
>> Monday   August 28, 2000   07:18pm
>>
>> Dear all,
>>
>> Many thanks for your interesting answers.
>>
>> I would like to ask to Felix Lorenz if
>> he thinks that a subgenus might be
>> a poliphyletic group.
>>
>> Ciao, Maurizio.
>>
>> ======================
>> Maurizio A. Perini
>> Via Pedrazza, 9
>> I - 36010 Zane (VI)
>> I T A L Y
>>
>> Voice  +39.0445.380378
>> F A X  +39.0445.598315
>> e-mail  [log in to unmask]
>> ======================
>>> Oliva Collecting & Study  <
>> ======================
>
============================================================
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