bignoni question

Thomas G. Lammers lammers at FMPPR.FMNH.ORG
Wed May 21 13:59:16 CDT 1997


Well, I don't really know Bignoniaceae that well, but at least its in the
Asteridae, so I'll take a shot at it.

At 12:00 PM 05-21-97 -0500, Jerome V Ward wrote:

>I have a question about Catalpa (Indian cigar tree).  We have two species
>in Alabama, C. bignonioides and C. speciosa which have somewhat
>overlapping ranges.  In the former the corolla is 3 cm or less and the
>latter ca 4 cm.  The bark is fissured in the latter but not the former.

There are additional characters typically cited in keys (e.g. Gray's Manual
ed. 8): leaf shape differences, shape of lower lower corolla lobe, shape of
the valves of the capsule.

> I would like to ask how easily these species can be
>separated?

The few times I've dealt with them, I've not had trouble.

> Wouldn't slight differences like this be a result of
>phenotypic plasticity?

There is absolutely NO correlation between degree of difference and its
genetic basis.  Wildly differing morphologies may be environmentally
inducible (as in many amphibious angiosperms), while things with
substantially genotypic differences, which are totally incapable of
producing fertile offspring, may be visually indistinguishable.   To check
for phenotypic plasticity, do classic reciprocal transplant experiments of
cloned individuals, a la  Clausen, et al.

>Since I don't know a lot about the genus I don't know if hybrids form.

I've not seen mention of any.

>My inclination would be to treat this as one species.

Remember that species make the characters, characters don't make the species.
In other words, it is the behavior of individuals in their environment that
determines whether or not we are dealing with one species or two in this case.

Do individuals exhibiting one sort of morphology most often exchange genes
only with each other and not with individuals of a different morphology?  Do
those same individuals inhabit a certain sort of habitat, growing best under
certain environmental conditions that are different from those in which
individuals of the other sort are found?  If so, we have two species,
irrespective of the degree of morphological differentiation.  For practical
reasons, we may choose to not formally name cryptic species, i.e., those
that meet these criteria but cannot be distinguished visually.  But they are
no less "real".


Thomas G. Lammers

Classification, Nomenclature, Phylogeny and Biogeography
of the Campanulaceae, s. lat.

Department of Botany
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, Illinois 60605-2496 USA

e-mail:     lammers at fmppr.fmnh.org
voice mail: 312-922-9410 ext. 317

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