[Taxacom] Paraphyletic groups as natural units of biological classification

Weakley, Alan weakley at bio.unc.edu
Sat Sep 27 22:09:11 CDT 2014

Here seems to be "the thing".  

The "basal angiosperms" or "primitive dicots" or "ANITA and the Magnoliids" or...  are clearly a basal grade to other angiosperms, based on all recent analyses.  Amborellales sister to all other angiosperms.  Then Nymphaeales sister to all the rest, then...  ETC.  Whether you have access to all the papers, a good summary of the current consensus can be had online at the Angiosperm Phylogeny Website, at MoBot, compiled by Peter Stevens.  This clearly shows a grade of various orders (all small, currently) and then also the magnoliids (mostly small, currently, except especially, the Lauraceae and somewhat less so the Piperaceae).

So, the "basal angiosperms" are not monophyletic.  And yet, it is "useful" and "convenient" to refer to them as a group -- to classify them as a unit.  In teaching, and in floras (Flora of Virginia 2012, Flora of the Southern and Mid-Atlantic States 2014)), it is "handy" ("useful") to divide the vascular flora into:  Lycophytes, Ferns, Basal Angiosperms, Monocots, and Eudicots.  It seems "disproportionate" to treat 4 or more units (small, currently, a genus or two, a hundred species or less, each) at equivalent rank to Monocots or Eudicots, which have many more orders, families, genera, and species.  Especially, as their morphological  differences seem relatively obscure, abstruse, and non-obvious.  If the morphological distinctions were completely obvious, maybe we would be more accepting -- no-one seems to have a hard time with Ginkgo or Welwitschia as (modern) monotypes:  uncontroversial monotypic orders.  

So, Judd et al., for instance, in their textbook, Plant Taxonomy: a Phylogenetic Approach, use quotes to indicate units that are not monophyletic but yet are "useful".  There is an interesting tension here between "strict monophyly" and "intuitive (useful) classification units".   Units with quotes seem to flag something like "this is not monophyletic but sure is handy so we will keep using it informally".

I'm not taking sides here (I am conflicted).  But...  it may be instructive to contemplate that other "intuitive (useful) classification units" ("plants", "animals", "algae", "fungi", "birds", "bacteria", "slime-molds", ) have fared increasingly poorly over time as real classification units.  I was taught as a college botany student in the 1970s that there were 2 main types of algae (a kind of plant):  prokaryotic ("blue-green algae") and eukaryotic (green, red, brown, etc., algae) --  several decades on, this looks laughable (and in no way "useful" or "convenient" in any respect).  On the other hand, the "Basal Angiosperms" seem a "useful" unit for teaching and organization and classification, even if monophyly is uncertain or even disproved...  

-----Original Message-----
From: Taxacom [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Curtis Clark
Sent: Saturday, September 27, 2014 9:29 PM
To: taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Paraphyletic groups as natural units of biological classification

On 2014-09-27 6:59 AM, John Grehan wrote:
> 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.

Some of its members (Austrobaileyaceae?) are more closely related to the rest of the angiosperms than others are. (Same definition as usual.)

Curtis Clark        http://www.csupomona.edu/~jcclark
Biological Sciences                   +1 909 869 4140
Cal Poly Pomona, Pomona CA 91768
Taxacom Mailing List
Taxacom at mailman.nhm.ku.edu
The Taxacom Archive back to 1992 may be searched at: http://taxacom.markmail.org

Celebrating 27 years of Taxacom in 2014.

More information about the Taxacom mailing list