nominal characters

[Eric Zurcher]

In message Tue, 4 Apr 1995 08:34:02 -0500,
  Richard Jensen <rjensen at SAINTMARYS.EDU>  writes:

> Even monocot/dicot doesn't work.  Degeneria, a dicot, typically has three
> cotyledons and the genus Centranthus (Valerianaceae) is variable (1,2, or
> 3).  I'm not sure if there are any monocots with more than one, but I
> wouldn't be surprised.
>
> So, the search continues for a truly nominal character.
>

Actually its pretty hard to think of good examples of "nominal" characters
as defined by Fortuner. (That is, characters for which states cannot be
ordered, and with characters involving the presence/absence of structures also
ruled out.) Surely the number of cotyledons could be construed as ordered
(at least in an abstract sense; whether it is biologically sensible to do so
is quite another matter). Similarly, annual vs. biennial -- the number of
years required for development -- could also be viewed as ordered. Perhaps
monoecious/dioecious/bisexual would qualify? No, this seems to involve both
presence or absence of structures and the number of sexes present (and
whenever we deal with numbers, ordering is implicit). Well then, perhaps
whether a particular structure disarticulates or is persistent? But here we
might quantify the force required, or look for the presence of abcission
layers.

Fortuner's original assertion -- "A truly nominal character cannot
be present in a valid species in more than one state" -- is meaningless
if "nominal" characters don't exist at all! Or perhaps we could state it in
a shorter form: "A truly nominal character cannot be present (FULL STOP)."

Cheers,

Eric Zurcher
CSIRO Division of Entomology
Canberra, Australia
E-mail: ericz at ento.csiro.au
Phone: +61 6 246 4218