Phylum Pteridophyta (classification modified)

Curtis Clark jcclark-lists at EARTHLINK.NET
Mon Mar 14 08:17:35 CST 2005

on 2005-03-14 08:01 Ken Kinman wrote:
> I just hope the
> strict cladists haven't insisted on formally naming the
> Hepaticopsida-Bryopsida clade, because it doesn't seem absolutely
> necessary and certainly isn't a done deal.

I agree with the latter; mosses seems to share too many apomorphies with
tracheophytes to make that cut-and-dried.

> ******************************************************* Sorry Curtis,
> but your latest suggestions won't work.  Combining Horneophytopsida,
> Aglaophyton, and Rhyniopsida into a single plesion would just make
> that plesion paraphyletic (which I'm sure you don't want).

Plesions are *supposed* to be paraphyletic--that's the whole point. IMO
basal fossil complexes such as that are notoriously difficult to sort
out, and a plesion preserves the knowledge gaps better than either a
formal paraphyletic group or a bunch of poorly-supported formal clades.

> Furthermore, Phylum Pinophyta is
> paraphyletic with respect Phylum Magnoliophyta, so you would also
> have to raise all the Pinophyte classes to phylum level.

Yeah, I noticed that after I hit the send button. But in fact they were
raised to phylum level in general botany texts quite a while ago, and I
seem to remember them being co-equal classes in Phylum Tracheophyta in
Dittmer's text from the 1960s.

Ironically, recent molecular evidence suggests that the gymnosperms
might be a clade.

> Anyway, I am quite happy with the above
> classification, although considering your suggestion, I just might
> slide Progymnospermopsida back into the base of Phylum Pinophyta (as
> I did in 1994).  It depends on which of the two options is supported
> by the most clear-cut synapomorphy (and if that is congruent with
> your "less egregious" criterion, all the better).

Putting the progymnosperms in a taxon with ferns is like including all
the synapsids *except* the pelycosaurs and anything basal to them in the
Mammalia, but leaving the pelycosaurs in the Reptilia. I supposed it all
depends on what features you think best show "divergence", but to me
that's the true measure of the arbitrariness of paraphyletic groups.

Curtis Clark        
Web Coordinator, Cal Poly Pomona                 +1 909 979 6371
Professor, Biological Sciences                   +1 909 869 4062

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