Species as "Hypotheses"

Paul van Rijckevorsel dipteryx at FREELER.NL
Mon Jul 12 22:53:38 CDT 2004

From: Ron Gatrelle <gatrelle at TILS-TTR.ORG>
> The ICZN glossary has two interesting and useful catagorical definitions
of taxon.

> A  "zoological taxon" is:  "A natural taxon of animals (which may, or may
> not, have had a name applied to it)."

> A "taxonomic taxon" is:  "A taxon (e.g. family, genus, species) including
> whatever nominal taxa and individuals a zoologist at any time considers it
> to contain in his or her endeavour to define the _boundaries_ of a
> zoological taxon (q.v.).  A taxonomic taxon is denoted by the valid name
> determined from the available names of its included nominal taxa."
> (Emphasis mine.)

+ + +
This seems to leave something to be desired from an editorial point of view
(is there also a definition of a "nominal taxon"?), but it does appear to
equate a taxon with a "family, genus, species", etc. This would always be
ranked (i.e. by default), unless it is not named. But hair splitting is the
order of the day.

Under the ICBN, also, a taxon can be unnamed (and possibly rankless), but
its status under the Code will be marginal at best. There was a proposal to
the Congress at StLouis (1999) to introduce rankless names (Art 16 prop H)
for rankless taxa into the ICBN: this was referred to a newly formed
Committee which has not reported yet. Also it is not impossible for unranked
names to be published. However, unless thus specified, a taxon will have a
rank (which will be indicated by a termination or a term denoting rank; Art
21.1, 24.1). The vast majority of taxa will have a rank, and the use of the
word taxon (heavily) implies that it has a rank: the exceptions will be
indicated as "unranked taxon" or whatever.

I am unsure if a taxon is necessarily a result of a phylogenetic process
[as in "their hypothetical evolutionary past. But with each ranked entity
itself we (should) have a taxon that is an observable product of the
process, a definable reality know not by hypothesis or theory but observable
factual _boundaries_.] Many taxa were created as containers for dubious
groups (e.g the family Euphorbiaceae) as no neat solution was available, as
a matter of convenience (shelved as unsolvable problems).

A taxon is a taxonomic group. The ICBN does not concern itself with what
taxonomic considerations have led to the taxonomic criteria for regarding it
as a group. A taxonomic consideration like "we will sweep these plants
together into this taxon, so they will be out of the way" may leave
something to be desired from a scientific point of view, but is in itself
fine by the Code. The Code concerns itself with the question what the name
of the taxon should be, not with the question if it is good science to
accept the taxon.

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