[Taxacom] Paraphyletic groups as natural units of biological classification

John Grehan calabar.john at gmail.com
Sat Sep 27 08:59:36 CDT 2014


Since you have some expertise and strong opinions on paraphyly I presume
you have read the citation of Stuessy (2010) on basal angiosperms being a
paraphyletic group. As I do not have immediate access to that paper perhaps
you could describe in what way that group was paraphyletic.


John Grehan

On Thu, Sep 25, 2014 at 8:52 PM, Kenneth Kinman <kinman at hotmail.com> wrote:

> Dear All,                         I was just rereading a 2010 paper by
> Horandl and Stuessy (published in the journal Taxon).  It should be
> required reading in any systematics course.  Below is the abstract.
>               --------------------Ken
> Hörandl, E. & Stuessy, T.F.  2010.  Paraphyletic groups as natural units
> ofbiological classification.  Taxon 59: 1641-1653.
> Despite the broad acceptance of phylogenetic principles in
> biologicalclassification, a fundamental question still exists on how to
> classifyparaphyletic groups. Much of the controversy appears due to (1)
> historicalshifts in terminology and definitions, (2) neglect of focusing on
> evolutionaryprocesses for understanding origins of natural taxa, (3) a
> narrow perspective ondimensions involved with reconstructing phylogeny, and
> (4) acceptance of lowerlevels of information content and practicability as
> a trade-off for ease ofarriving at formal classifications. Monophyly in
> evolutionary biology originallyhad a broader definition, that of describing
> a group with common ancestry. Thisdefinition thus includes both
> paraphyletic and monophyletic groups in the senseof Hennig. We advocate
> returning to a broader definition, supporting use ofAshlock's term
> holophyly as replacement for monophyly s.str. By reviewingprocesses
> involved in the production of phylogenetic patterns (budding, merging,and
> splitting), we demonstrate that paraphyly is a natural transitional stage
> inthe evolution of taxa, and that it occurs regularly along with holophyly.
> When a new holophyletic group arises, it usually coexists for some time
> with itsparaphyletic stem group. Paraphyly and holophyly, therefore,
> representrelational and temporal evolutionary stages. Paraphyletic groups
> exist at alllevels of diversification in all kingdoms of eukaryotes, and
> they havetraditionally been recognized because of their descent-based
> similarity. Wereview different methodological approaches for recognition of
> monophyleticgroups s.l. (i.e., both holophyletic and paraphyletic), which
> are essential fordiscriminating from polyphyly that is unacceptable in
> classification. Forarriving at taxonomic decisions, natural processes,
> information content, andpracticability are essential criteria. We stress
> using shared descent as aprimary grouping principle, but also emphasize the
> importance of degrees ofdivergence plus similarity (cohesiveness of
> evolutionary features) as additionalcriteria for classification.
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