Bad taxonomic keys

[Wolfgang Wuster]

On Sun, 1 Oct 1995, Robin Panza wrote:
> Joseph Laferriere wrote:
> >available. I once saw a key separating two genera using the following
> >couplet:
> >
> >Embryo curved
> >Embryo straight
> >
> >The seeds of both taxa were about a millimeter in diameter. Another book
> >separated the exact same genera thus:
> >
> >Inflorescence a spike
> >Infloresence a panicle
> >
> >Which would you rather use? Embryo shape might be a more useful character
> >in determining the relationships of these genera to other groups, but
> >inflorescence shape is infinitely easier to determine.
>
> This argument is self-contradicting.  The very fact that a particular specimen
> is damaged is exactly why the key's creator cannot hope to make a key for all
> uses.  Granted, inflorescence shape is more likely to be of use on future
> identifications.  Granted, if seed and inflorescence are both available, the
> latter would still be easier to use.  However, if I had to do an environmental
> survey right now (fall, around here), I couldn't possibly identify this plant
> based on inflorescence shape.  I would be better off with the embryo character.
[snip]

Surely the answer to this is obvious: all characters which can
discriminate between the two species should be included in the key. In the
case of Joseph's taxa, include both embryo shape *and* inflorescence shape.
That way, you get an all-weather, all-seasons key. The same should apply
to any other organisms - include several different characters, including
those easiest to use, as well as some which are likely to remain
present  even if the easier character are destroyed or absent for
seasonal reasons.

--
Wolfgang Wuster
School of Biological Sciences, University of Wales, Bangor, UK
e-mail: bss166 at bangor.ac.uk

Thought for the day: If you see a light at the end of the tunnel,
it is probably a train coming your way.