your mail

Joseph Laferriere josephl at CCIT.ARIZONA.EDU
Tue Sep 5 08:06:39 CDT 1995

I am afraid I disagree with both of you. This "not as above" method of
writing keys may make them easier to write, but it makes them extremely
difficult to use. It is sometimes necessary to do this, but it should be
done only as a last resort. I have seen long keys to complex groups
composed solely along the "not as above" method, which require inhuman
patience to use.

On Fri, 1 Sep 1995, Mike Crisp wrote:

> Richard Jensen says:
> >I disagree with Murray Fletcher's view that any couplet having "not as
> >above" is a poor couplet.  Some (many, most?) taxa are polythetic entities
> >or are especially variable in individual characters - a simple way to
> >isolate them in a key (rather than following them through all possible
> >leads) is to specify the combination of characters that allows
> >identification.  As long as no other taxon in the key has that precise
> >combination of features, then the couplet works, and that's one key to a
> >good key.
> I agree.
> I use 'not as above' frequently for taxa that have obvious diagnostic
> characters but otherwise have nasty combinations of characters that don't
> allow them to fall into either group of a major split I want to make
> further down in the key.  If a taxon is very distinctive, either by virtue
> of its autapomorphic characters or, as R.J. says, a unique combination,
> then the meaning of 'not as above' is clear.

More information about the Taxacom mailing list