[Taxacom] Paraphyletic groups as natural units of biological classification

Sat Sep 27 23:08:03 CDT 2014

Put another way.

And see:  http://www.mobot.org/MOBOT/research/APweb/

If, in vascular plants, one wanted to create a broad set of groups useful for classification, teaching, recognition, etc., one might want to recognize:

1.  Lycophytes
2.  Ferns
3.  "Basal angiosperms"
4.  Monocots
5.  "Basal Eudicots"
6.  Rosids s.l.
7.  Asterids s.l.

Each of these is diagnosable morphologically, and each has a clear evolutionary position relative to the others.  But 3 and 5 are not monophyletic, they are grades (as based on current phylogenetic reconstructions):  3 a grade relative to clade 4+5+6+7, and 5 a grade relative to clade 6+7.  Making the entities in grade 3 separate monophyletic units makes an additional 3 or more units.  Making the entities in grade 5  separate monophyletic entities makes 5-6 (or more) additional units.  1 is monophyletic, but includes very ancient (Devonian) (and morphologically easily distinguishable) entities.

So, with good basis and with (only a little) less angiosperm bias, one could easily substitute for 1-7 above, and with strict monophyly:

1.  Huperziaceae
2.  Lycopodiceae
3.  Equisetaceae
4.  Psilotaceae
5.  Ophioglossaceae
6.  Horsetails
7.  Ferns
8.  Amborella trichopoda (1 species)
9.  Nymphaeaceae
10.  Austrobaileyales
11.  Magnoliales 
12.  Monocots
13.  Ceratophyllum (6 species)
14.  Ranunculales
15.  Proteales
16.  Trochodendrales
17.  Buxales
18.  Gunnerales
19.  Dilleniaceae
20.  "Rosids"
21.  Santalales
22.  Berberidopsidales
23.  Caryophyllales
24.  Cornales
25.  Ericales
26.  "Asterids"

Note that while each of 1-7 are monophyletic, each contains divisions (not shown) that are older and "more fundamental" than any of those in 9-26.  

-----Original Message-----
From: Taxacom [mailto:taxacom-bounces at mailman.nhm.ku.edu] On Behalf Of Weakley, Alan
Sent: Saturday, September 27, 2014 11:09 PM
To: Curtis Clark; taxacom at mailman.nhm.ku.edu
Subject: Re: [Taxacom] Paraphyletic groups as natural units of biological classification

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
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