Monophyly and herbaria - changing minds

Subject: BRYONET: Monophyly and herbaria
Date: Thu, 13 Nov 2008 08:44:51 -0600
From: Richard Zander <Richard.Zander@mobot.org>

BRYONET

There have been declarations that the arguments of the present thread on
paraphyly and phylogenetics will not change minds. What might be the
real basis of intransigence in the face of apparently cogent arguments
on either side?

Could it be a simple, practical choice is what is being wrestled over?
Some want to classify according to groupings of clades and nought else
(phylogeneticists), others tacking on rank changes for unique traits
(evolutionary taxonomists).

Is this something like an argument over which is the best way to arrange
an herbarium, alphabetically or "naturally" e.g. Bentham and Hooker, or
Engler, or Thorne, or whoever has the latest broad classification?
Alphabetical arrangements are immensely convenient but larger groupings
are exploded; but natural arrangements group genera into families so
someone who studies a family has them all together. Some arrange the
families by a natural linear arrangement, but put genera under the
families alphabetically, which is a nice compromise.

Monophyly is not a theory, but a system of classification, in my opinion
adopted so lineages alone can be the basis of classification. There is
no force in Nature called monophyly that requires a new genus to
diversify its lineage only as a sister group to another genus, or a new
family to be only a sister group to another family. Given this, then
there is a choice between monophyly and paraphyly in classification that
can be idiosyncratic. It is more library science than systematics.

Phylogenetics has contributed a fine method of analyzing morphological
relationships (parsimony) on the basis of some but not all
evolutionarily important traits, and of distinguishing molecular genetic
continuity and isolation. I submit that phylogenetic adherence to
monophyly in classification, however, excises equally important
information on new evolutionary directions (nonmonophyletic genera and
families). If the Pottiaceae were represented in a future floristic book
following the MPG III, then there would be no diagnoses of Ephemeraceae,
Splachnobryaceae or Cinclidotaceae.

Biodiversity measures and triage decisions are now commonly based on
phylogenetic (patristic) distance between lineages (that is, summing the
intermediate branch lengths is a measure of how long clades have evolved
away from each other), but not how much clades or taxa have evolved and
in what unique respects.

Is this the difference between two camps, how we are to arrange our
herbaria? At what cost to science?

*****************************
Richard H. Zander
Voice: 314-577-0276
Missouri Botanical Garden
PO Box 299
St. Louis, MO 63166-0299 USA
richard.zander@mobot.org
Web sites: http://www.mobot.org/plantscience/resbot/
and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
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