nominal characters

[Richard Jensen]

It seems to me that any nominal character can be viewed as
presence/absence; e.g., ossified skeleton present/absent provides the
same dichotomy as cartilaginous/ossified skeleton.

Whether or not a nominal character can have two states within a species
depends on whether or not the character plays a role in diagnosing the
species.  For example, in some species the leaves are decidedly
obtrullate while in other species the leaves are decidedly ovate (and, in
each case, the two conditions are mutually exclusive).  But, in some
other species, both conditions are found.  This occurs in Quercus and I
am sure there are other examples.  Of course, you may argue that this
refers to leaf shape which is not truly nominal - within the genus there
is a complete series from ovate to obtrullate.  But I'm not sure that
there is a logical ordering for these shapes.  It may be logical
mathematically, but that is not the same as logical biologically.

Are there any truly nominal characters, as defined by Fortuner?  In oaks,
again, I might claim that fruit maturation is a nominal character, either
annual or biennial.  Yet, there is at least one species (and no one has
suggested it is not a good species) which appears to have both states.  I
know of no third state for this character.  So, I would argue that this
is a good example of a nominal character of two states for which both
states occur in a single species.

But, the situation is not so clear.  My suspicion is that those plants
exhibiting biennial maturation are the result of hybridization of the
normally annually fruited species with a biennially fruited species.
But, the putative hybrids appear, in virtually all other characters, to
be typical representatives of the annuall fruited taxon.


Dick

Richard J. Jensen      |   E-MAIL: rjensen at saintmarys.edu
Dept. of Biology       |   TELEPHONE: 219-284-4674
Saint Mary's College   |   FAX: 219-284-4716
Notre Dame, IN  46556  |