[Taxacom] another recent article in Taxon

Richard Zander Richard.Zander at mobot.org
Mon Mar 28 12:27:51 CDT 2011

The Stuessy and Hörandl 2010 paper is somewhat biased towards Stuessy's past as a puissant purveyor of phenetics. For Stuessy, the dendrogram still has manna. This is why he is content to use phylogenetic terms like paraphyly and phylogenetic polyphyly (quite different from evolutionary polyphyly) which are entirely based on positions of the exemplars on a dendrogram, not in a macroevolutionary tree that shows one taxon derived from another (diagnosable) taxon.

Only somewhat biased, as many of the things they say are valuable.

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Richard H. Zander 
Missouri Botanical Garden, PO Box 299, St. Louis, MO 63166-0299 USA 
Web sites: http://www.mobot.org/plantscience/resbot/ and http://www.mobot.org/plantscience/bfna/bfnamenu.htm
Modern Evolutionary Systematics Web site: http://www.mobot.org/plantscience/resbot/21EvSy.htm

-----Original Message-----
From: taxacom-bounces at mailman.nhm.ku.edu [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Kenneth Kinman
Sent: Monday, March 28, 2011 9:37 AM
To: taxacom at mailman.nhm.ku.edu
Subject: [Taxacom] another recent article in Taxon

Dear All,
       Another very interesting paper was recently (December 2010) published in the journal Taxon.  For those who haven't seen it, especially zoologists who don't normally read botanical journals, the abstract is given below.
Hörandl, E. & Stuessy, T.F.  2010.  Paraphyletic groups as natural units of biological classification.  Taxon 59: 1641-1653. 
Despite the broad acceptance of phylogenetic principles in biological classification, a fundamental question still exists on how to classify paraphyletic groups. Much of the controversy appears due to (1) historical shifts in terminology and definitions, (2) neglect of focusing on evolutionary processes for understanding origins of natural taxa, (3) a narrow perspective on dimensions involved with reconstructing phylogeny, and (4) acceptance of lower levels of information content and practicability as a trade-off for ease of arriving at formal classifications. Monophyly in evolutionary biology originally had a broader definition, that of describing a group with common ancestry. This definition thus includes both paraphyletic and monophyletic groups in the sense of Hennig. We advocate returning to a broader definition, supporting use of Ashlock's term holophyly as replacement for monophyly s.str. By reviewing processes involved in the production of phylogenetic patterns (budding, merging, and splitting), we demonstrate that paraphyly is a natural transitional stage in the evolution of taxa, and that it occurs regularly along with holophyly.
When a new holophyletic group arises, it usually coexists for some time with its paraphyletic stem group. Paraphyly and holophyly, therefore, represent relational and temporal evolutionary stages. Paraphyletic groups exist at all levels of diversification in all kingdoms of eukaryotes, and they have traditionally been recognized because of their descent-based similarity. We review different methodological approaches for recognition of monophyletic groups s.l. (i.e., both holophyletic and paraphyletic), which are essential for discriminating from polyphyly that is unacceptable in classification. For arriving at taxonomic decisions, natural processes, information content, and practicability are essential criteria. We stress using shared descent as a primary grouping principle, but also emphasize the importance of degrees of divergence plus similarity (cohesiveness of evolutionary features) as additional criteria for classification.

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