Variable character states (Use of the rank of forma)

[Hubert Turner]

On Wed, 04 Oct 2000 09:44:07 +0100, Zdenek Skala
<Zdenek.Skala at INCOMA.CZ> wrote:
>BTW, the infraspecific taxonomy can often contribute also to the
>cladistic analysis, since it is often hard to find even one species-
>specific character that is *really* invariable... (think about the
>homeotic variations in flower plan etc.). This is a good point to
>show how the methodology utilized drives our theoretical thoughts -
>in cladistic analysis we need morpologically homogeneous
>operational units, so we create them :-)
I feel that a distinction should be made between the actual traits
observed in individual specimens (flowers scarlet, flowers pale red,
flowers pinkish, flowers purplish, flowers white) and the character
state assigned to the operational unit. The latter should be the
state with which it was 'born', rather than a subsequent modification
of that state. Thus, the unit might be assigned the state 'flowers
red' even though individuals vary in their particular shade of red,
and some are actually white-flowered due to a (recent?) mutation.
Cladistics is about inheritable character states, which in the end
boil down to particular DNA (or RNA) sequences. And U's or C's don't
come in many different shades. No variability there, they actually
are U's or C's.
For literature on 'discrete' character states actually being
abstractions of ranges, see e.g. P.F. Stevens, (1991) Syst. Bot.
16:553; on polymorphism, papers by J.J. Wiens and my reply in Syst.
Biol. 48 (1999) 365.
--

Hubert Turner

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Dr. H. Turner
EEW, Sect. Theoretical Biology & Phylogenetics
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